| Masaki Tanaka | Last modified date：2024.04.19 |
Professor /
Metals Science for Structural Materials /
Department of Materials Science and Engineering /
Faculty of Engineering
Papers
| 1. | , [URL].  |
| 2. | Bhargavi Rani Anne, Yelm Okuyama, Tatsuya Morikawa, Masaki Tanaka, Activated slip systems in bimodal Ti–6Al–4V plastically deformed at low and moderately high temperatures, Materials Science and Engineering A, 10.1016/j.msea.2020.140211, 798, 2020.11. |
| 3. | Masaki Tanaka, Toshiyuki Manabe, Tatsuya Morikawa, Kenji Higashida, Mechanism behind the Onset of Delamination in Wire-drawn Pearlitic Steels, ISIJ International, 10.2355/isijinternational.ISIJINT-2020-158, 60, 11, 2596-2603, 2020.11. |
| 4. | Yelm Okuyama, Masaki Tanaka, Tetsuya Ohashi, Tatsuya Morikawa, Modelling and crystal plasticity analysis for the mechanical response of alloys with non-uniformly distributed secondary particles, ISIJ International, 10.2355/isijinternational.ISIJINT-2019-754, 60, 8, 1819-1828, 2020.08. |
| 5. | Muhammad Kozin, Keisuke Kusakabe, Masatoshi Aramaki, Naoya Yamada, Satoshi Oue, Yukiko Ozaki, Osamu Furukimi, Masaki Tanaka, Effect of nitriding-quenching and carburizing-quenching processes on the wear resistance of the sintered pure iron, Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy, 10.2497/jjspm.67.173, 67, 4, 173-181, 2020.04. |
| 6. | Investigation of strain redistribution mechanism in α titanium by image-based crystal plasticity analysis Abstract: Mechanisms of strain localization and localized activation of slip systems in α titanium were investigated using a crystal plasticity finite element (CPFE) method. A microscopic image of polycrystalline α titanium was obtained by electron back scatter diffraction (EBSD), and the data was converted from the microscopic image into the geometric model for the CPFE analysis. The uniaxial tensile deformation of the model was numerically reproduced by the CPFE method employing a dislocation density based constitutive equation. The results showed that the strain distribution corresponds well with that obtained by the experiment when the ratio of critical resolved shear stress (CRSS) employed in the numerical simulation is basal:prismatic ⟨a⟩:1st-pyramidal ⟨a⟩:1st-pyramidal ⟨c + a⟩:2nd-pyramidal ⟨c + a⟩ = 1.0:1.0:1.3:2.0:2.0. Next, numerical simulations were performed by changing the ratio of CRSS among the slip systems but keeping all other conditions the same as those of the above uniaxial tensile analysis. The results showed that strain redistribution typically occurs between hard and soft regions with high and low CRSSs for the primary slip systems; this redistribution resulted in a localized higher strain and activation of slip systems. However, localized activation of slip systems was observed even in slip systems with higher CRSS; the mechanism could be explained by the strain redistribution in the tensile direction. Graphical abstract: [Figure not available: see fulltext.].. |
| 7. | Investigation of strain redistribution mechanism in α titanium by image-based crystal plasticity analysis Abstract: Mechanisms of strain localization and localized activation of slip systems in α titanium were investigated using a crystal plasticity finite element (CPFE) method. A microscopic image of polycrystalline α titanium was obtained by electron back scatter diffraction (EBSD), and the data was converted from the microscopic image into the geometric model for the CPFE analysis. The uniaxial tensile deformation of the model was numerically reproduced by the CPFE method employing a dislocation density based constitutive equation. The results showed that the strain distribution corresponds well with that obtained by the experiment when the ratio of critical resolved shear stress (CRSS) employed in the numerical simulation is basal:prismatic ⟨a⟩:1st-pyramidal ⟨a⟩:1st-pyramidal ⟨c + a⟩:2nd-pyramidal ⟨c + a⟩ = 1.0:1.0:1.3:2.0:2.0. Next, numerical simulations were performed by changing the ratio of CRSS among the slip systems but keeping all other conditions the same as those of the above uniaxial tensile analysis. The results showed that strain redistribution typically occurs between hard and soft regions with high and low CRSSs for the primary slip systems; this redistribution resulted in a localized higher strain and activation of slip systems. However, localized activation of slip systems was observed even in slip systems with higher CRSS; the mechanism could be explained by the strain redistribution in the tensile direction. Graphical abstract: [Figure not available: see fulltext.].. |
| 8. | Temperature dependence of the yield stress in α-titanium investigated with crystal plasticity analysis © 2018 Trans Tech Publications, Switzerland. The effect of the activated slip systems on the temperature dependence of yield stress was investigated in α-Ti by using crystal plasticity finite element method. A model for finite element analysis (FEA) was constructed based on experimental results. The displacement in FEA was applied up to the nominal strain of 4% which is the same strain as the experimental one. Stress-strain curves were obtained, which corresponds to experimental data taken every 50 K between 73 K and 673 K. The used material constants which are temperature dependent were elastic constants, and lattice friction stresses. The lattice friction stresses of basal slip systems were set to be higher than that of pyramidal slip systems at 73 K. Then, the lattice friction stresses were set to be closer as the temperature increases. It was found that the activation of slip systems is strong temperature dependent, and that the yield stress depends on the number of active slip systems.. |
| 9. | Temperature dependence of the yield stress in α-titanium investigated with crystal plasticity analysis © 2018 Trans Tech Publications, Switzerland. The effect of the activated slip systems on the temperature dependence of yield stress was investigated in α-Ti by using crystal plasticity finite element method. A model for finite element analysis (FEA) was constructed based on experimental results. The displacement in FEA was applied up to the nominal strain of 4% which is the same strain as the experimental one. Stress-strain curves were obtained, which corresponds to experimental data taken every 50 K between 73 K and 673 K. The used material constants which are temperature dependent were elastic constants, and lattice friction stresses. The lattice friction stresses of basal slip systems were set to be higher than that of pyramidal slip systems at 73 K. Then, the lattice friction stresses were set to be closer as the temperature increases. It was found that the activation of slip systems is strong temperature dependent, and that the yield stress depends on the number of active slip systems.. |
| 10. | Development of a EBSD-FEM data conversion interface and the image-based crystal plasticity analysis. |
| 11. | Jun Fujise, Bonggyun Ko, Toshiaki Ono, Masaki Tanaka, Measurement and empirical equation of critical stresses for slip generation from oxide precipitates in silicon wafers, Japanese Journal of Applied Physics, 10.7567/JJAP.57.035501, 57, 3, 2018.03. |
| 12. | Bhargavi Rani Anne, Masaki Tanaka, Tatsuya Morikawa, Temperature dependence of mechanical properties in dual phase ti-6al-4v, 10th International Conference on Processing and Manufacturing of Advanced Materials, 2018 THERMEC 2018, 10.4028/www.scientific.net/MSF.941.1479, 1479-1483, 2018.01. |
| 13. | Yelm Okuyama, Masaki Tanaka, Tetsuya Ohashi, Tatsuya Morikawa, Temperature dependence of the yield stress in α-titanium investigated with crystal plasticity analysis, 10th International Conference on Processing and Manufacturing of Advanced Materials, 2018 THERMEC 2018, 10.4028/www.scientific.net/MSF.941.1474, 1474-1478, 2018.01. |
| 14. | Tanaka M, Izumi D, Yoshimura N, Shigesato G, Hoshino M, Ushioda K, Higashida K, Temperature dependence of activation volume on Cu content of ultra-low carbon steel, Philosophical Magazine, 10.1080/14786435.2017.1359423, 97, 31, 2915-2930, Vol. 97, pp.2951-2930, 2017.11, [URL]. |
| 15. | Tanaka M, Izumi D, Yoshimura N, Shigesato G, Hoshino M, Ushioda K, Higashida K, Temperature dependence of activation volume on Cu content of ultra-low carbon steel, Philosophical Magazine, 10.1080/14786435.2017.1359423, 97, 31, 2915-2930, 2017.11. |
| 16. | Nobuyuki Yoshimura, Kohsaku Ushioda, Mitsuharu Yonemura, Motomichi Koyama, Masaki Tanaka, Hiroshi Noguchi, Effect of the state of carbon on ductility in Fe-0.017mass%C ferritic steel, Materials Science and Engineering A, 10.1016/j.msea.2017.06.070, 701, 120-128, Vol.701, pp.120-128, 2017.07, [URL]. |
| 17. | Osamu Furukimi, Chatcharit Kiattisaksri, Yuji Takeda, Masatoshi Aramaki, Satoshi Oue, Shinji Munetoh, Masaki Tanaka, Void nucleation behavior of single-crystal high-purity iron specimens subjected to tensile deformation, Materials Science and Engineering A, 10.1016/j.msea.2017.06.084, 701, 221-225, Vol. 701, pp.120-128, 2017.07, [URL]. |
| 18. | Nobuyuki Yoshimura, Kohsaku Ushioda, Mitsuharu Yonemura, Motomichi Koyama, Masaki Tanaka, Hiroshi Noguchi, Effect of the state of carbon on ductility in Fe-0.017mass%C ferritic steel, Materials Science and Engineering A, 10.1016/j.msea.2017.06.070, 701, 120-128, 2017.07. |
| 19. | Osamu Furukimi, Chatcharit Kiattisaksri, Yuji Takeda, Masatoshi Aramaki, Satoshi Oue, Shinji Munetoh, Masaki Tanaka, Void nucleation behavior of single-crystal high-purity iron specimens subjected to tensile deformation, Materials Science and Engineering A, 10.1016/j.msea.2017.06.084, 701, 221-225, 2017.07. |
| 20. | Hiroshi Kaneko, Tatsuya Morikawa, Masaki Tanaka, Hirofumi Inoue, Kenji Higashida, Recrystallization texture and shear band formation in bending, Materials Transactions, 10.2320/matertrans.M2016363, 58, 2, 218-224, 2017.02. |
| 21. | Masaki Tanaka, Kenta Matsuo, Nobuyuki Yoshimura, Genichi Shigesato, Manabu Hoshino, Kohsaku Ushioda, Kenji Higashida, Effects of Ni and Mn on brittle-to-ductile transition in ultralow-carbon steels, Materials Science and Engineering A, 10.1016/j.msea.2016.11.045, 682, 370-375, 2017.01. |
| 22. | Masaki Tanaka, Kenji Higashida, Temperature dependence of effective stress in severely deformed ultralow-carbon steel, Philosophical Magazine, 10.1080/14786435.2016.1183828, 96, 19, 1979-1992, Vol. 96, pp.1979-1992, 2016.07, [URL]. |
| 23. | Masaki Tanaka, Kenji Higashida, Temperature dependence of effective stress in severely deformed ultralow-carbon steel, Philosophical Magazine, 10.1080/14786435.2016.1183828, 96, 19, 1979-1992, 2016.07, © 2016 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group. The effects of severe plastic deformation on the thermal activation of dislocation gliding in ultralow-carbon steel at low temperatures were investigated. This was done by measuring the temperature dependences of the effective stress, activation volume and activation energy. It was found that the values of all these parameters were lower than those for coarse-grained specimens at low temperatures. In coarse-grained materials, the activation energy should increase with a decrease in the effective stress. This phenomenon, which seemed counterintuitive initially, could be physically interpreted on the basis of the fluctuation in the athermal stress.. |
| 24. | Sadamatsu S, Tanaka M, Higashida K, Matsumura S, Transmission electron microscopy of bulk specimens over 10μm in thickness, Ultramicroscopy, 10.1016/j.ultramic.2015.09.001, 162, 10-16, 2016.03. |
| 25. | Masaki Tanaka, Hayato Saito, Motoki Yasumaru, Kenji Higashida, Nature of delamination cracks in pearlitic steels, Scripta Materialia, 10.1016/j.scriptamat.2015.09.004, 112, 32-36, 2016.02. |
| 26. | Damar Rastri Adhika, Masaki Tanaka, Takeshi Daio, Kenji Higashida, Crack tip shielding observed with high-resolution transmission electron microscopy, Microscopy, 10.1093/jmicro/dfv032, 64, 5, 335-340, 2015.10. |
| 27. | Damar Rastri Adhika, Masaki Tanaka, Kenji Higashida, Strain Field Around Lomer Sessile Dislocations in Silicon Measured using Geometric Phase Analysis, Trans. Mater. Res. Soc. Japan, Vol.40, pp.227-233,, 10.14723/tmrsj.40.227, 2015.08, [URL]. |
| 28. | Takeshi Daio, Aleksandar Staykov, Limin Guo, Jianfeng Liu, Masaki Tanaka, Stephen Matthew Lyth, Kazunari Sasaki, Lattice Strain Mapping of Platinum Nanoparticles on Carbon and SnO 2 Supports, Scientific Reports, 10.1038/srep13126, 5, 2015.08. |
| 29. | Damar Rastri Adhika, Masaki Tanaka, Kenji Higashida, Strain Field Around Lomer Sessile Dislocations in Silicon Measured using Geometric Phase Analysis, Trans. Mater. Res. Soc. Japan, Vol.40, pp.227-233,, 10.14723/tmrsj.40.227, 2015.08. |
| 30. | , [URL]. |
| 31. | Thiti Sirithanakorn, Masaki Tanaka, Kenji Higashida, Brittle-to-ductile transitions and its relation to the deformability of cementite in fully pearlitic steels, Materials Science and Engineering A, 10.1016/j.msea.2014.06.007, 611, 383-387, 2014.08. |
| 32. | Masaki Tanaka, Tatsuro Onomoto, Chihiro Furusho, Toshihiro Tsuchiyama, Kenji Higashida, Decrease in the Brittle-to-ductile Transition Temperature in Cu Added Nickel-free Austenitic Stainless Steels, ISIJ INTERNATIONAL, 10.2355/isijinternational.54.1735, 54, 7, 1735-1740, 2014.07. |
| 33. | , [URL]. |
| 34. | Thiti Sirthanakorn, Masaki Tanaka, Kenji Higashida, Two-step brittle-to-ductile transitions in pearlitic steels, Advanced Materials Research, 10.4028/www.scientific.net/AMR.922.706, 922, 706-710, 2014.05, [URL]. |
| 35. | Thiti Sirthanakorn, Masaki Tanaka, Kenji Higashida, Two-step brittle-to-ductile transitions in pearlitic steels, Advanced Materials Research, 10.4028/www.scientific.net/AMR.922.706, 922, 706-710, 2014.05. |
| 36. | Tomotsugu Shimokawa, Takuma Oguro, Masaki Tanaka, Kenji Higashida, Tetsuya Ohashi, A multiscale approach for the deformation mechanism in pearlite microstructure: Atomistic study of the role of the heterointerface on ductility, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 10.1016/j.msea.2013.12.100, 598, 68-76, Vol.598, pp.68-76, 2014.03, [URL]. |
| 37. | Tomotsugu Shimokawa, Takuma Oguro, Masaki Tanaka, Kenji Higashida, Tetsuya Ohashi, A multiscale approach for the deformation mechanism in pearlite microstructure: Atomistic study of the role of the heterointerface on ductility, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 10.1016/j.msea.2013.12.100, 598, 68-76, 2014.03. |
| 38. | Masaki Tanaka, Atsushi Fujii, Hiroshi Noguchi, Kenji Higashida, Thermally activated processes of fatigue crack growth in steels, PHILOSOPHICAL MAGAZINE LETTERS, 10.1080/09500839.2013.872811, 94, 2, 95-102, 2014.02, [URL]. |
| 39. | Masaki Tanaka, Atsushi Fujii, Hiroshi Noguchi, Kenji Higashida, Thermally activated processes of fatigue crack growth in steels, PHILOSOPHICAL MAGAZINE LETTERS, 10.1080/09500839.2013.872811, 94, 2, 95-102, 2014.02, Fatigue crack growth rates in steels at high and low temperatures have been investigated using Paris curves. The fatigue crack growth rates at high temperatures are quite different from those at low temperatures. Arrhenius plots between fatigue crack growth rate (da/dN) and test temperatures at constant stress intensity factor range (K-I) indicate a difference of the rate-controlling process for fatigue crack growth with temperature. Slip deformation at the crack tip governs fatigue crack growth at high temperatures, while hydrogen diffusion is associated with crack growth at low temperatures.. |
| 40. | Masaki Tanaka, Yusuke Yoshimi, Kenji Higashida, Tomotsugu Shimokawa, Tetsuya Ohashi, A multiscale approach for the deformation mechanism in pearlite microstructure: Experimental measurements of strain distribution using a novel technique of precision markers, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 10.1016/j.msea.2013.09.072, 590, 37-43, 590, pp.37-43, 2014.01, [URL]. |
| 41. | G. S. Liu, S. D. House, J. Kacher, M. Tanaka, K. Higashida, I. M. Robertson, Electron tomography of dislocation structures, MATERIALS CHARACTERIZATION, 10.1016/j.matchar.2013.09.016, 87, 1-11, 2014.01. |
| 42. | Masaki Tanaka, Yusuke Yoshimi, Kenji Higashida, Tomotsugu Shimokawa, Tetsuya Ohashi, A multiscale approach for the deformation mechanism in pearlite microstructure: Experimental measurements of strain distribution using a novel technique of precision markers, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 10.1016/j.msea.2013.09.072, 590, 37-43, 2014.01, Plastic deformation of fully pearlitic steels was investigated using a multiscale approach: experimentally, the finite element method and molecular dynamics. This paper is the first in a series of three papers demonstrating the strain distribution in uniaxial tensile deformation with high-precision markers drawn by electron beam lithography. Strain was measured at loads of 1.98 kN, 2.21 kN and 2.28 kN in tensile deformation. Scanning electron microscopy (SEM) images and strain maps show the plastic deformation of cementite lamellae and homogenous plastic deformation under uniaxial tensile deformation in the area where the cementite lamellae are aligned in the tensile direction. The areas where strain was enhanced were both block/colony boundaries and the areas where the cementite lamellae are inclined approximately 45 degrees to the tensile direction. (C) 2013 Elsevier B.V. All rights reserved.. |
| 43. | G. S. Liu, S. D. House, J. Kacher, M. Tanaka, K. Higashida, I. M. Robertson, Electron tomography of dislocation structures, MATERIALS CHARACTERIZATION, 10.1016/j.matchar.2013.09.016, 87, 1-11, 2014.01, Recent developments in the application of electron tomography for characterizing microstructures in crystalline solids are described. The underlying principles for electron tomography are presented in the context of typical challenges in adapting the technique to crystalline systems and in using diffraction contrast imaging conditions. Methods for overcoming the limitations associated with the angular range, the number of acquired images, and uniformity of image contrast are introduced. In addition, a method for incorporating the real space coordinate system into the tomogram is presented. As the approach emphasizes development of experimental solutions to the challenges, the solutions developed and implemented are presented in the form of examples. (C) 2013 Elsevier Inc. All rights reserved.. |
| 44. | Tetsuya Ohashi, Lidyana Roslan, Kohsuke Takahashi, Tomotsugu Shimokawa, Masaki Tanaka, Kenji Higashida, A multiscale approach for the deformation mechanism in pearlite microstructure: Numerical evaluation of elasto-plastic deformation in fine lamellar structures, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 10.1016/j.msea.2013.09.032, 588, 214-220, Vol.588, pp.214-220, 2013.12, [URL]. |
| 45. | Tetsuya Ohashi, Lidyana Roslan, Kohsuke Takahashi, Tomotsugu Shimokawa, Masaki Tanaka, Kenji Higashida, A multiscale approach for the deformation mechanism in pearlite microstructure: Numerical evaluation of elasto-plastic deformation in fine lamellar structures, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 10.1016/j.msea.2013.09.032, 588, 214-220, 2013.12, Elasto-plastic deformations in the microstructures of pearlite are studied by finite-element analyses. Various models for the lamellar structure are made and the material properties of cementite and ferrite are established. Deformation of a bare specimen of cementite is unstable immediately after the yield point, while cementite lamellae show some stability when they are layered with ferrite. When higher values of yield stress and strain hardening are used for ferrite phase, cementite deforms well beyond the elastic range and the distribution of plastic strain is not concentrated. These results show that not only the layered structure but also the improved mechanical property of fine lamellae of ferrite contribute largely to stable deformation in the pearlite microstructure. (C) 2013 Elsevier B.V. All rights reserved.. |
| 46. | Masaki Tanaka, Shunsaku Takano, Kenji Higashida, Enhancement of Low Temperature Toughness in Bulk Nanostructured Metals, MATERIALS TRANSACTIONS, 10.2320/matertrans.MH201319, 54, 9, 1624-1628, Vol. 54, No.9, pp.1624-1628, 2013.09, [URL]. |
| 47. | Masaki Tanaka, Naoya Kamikawa, Nobuhiro Tsuji, Special Issue on Advanced Materials Science in Bulk Nanostructured Metals II PREFACE, MATERIALS TRANSACTIONS, 10.2320/matertrans.MPR2013906, 54, 9, 1539-1539, 2013.09. |
| 48. | Masaki Tanaka, Shunsaku Takano, Kenji Higashida, Enhancement of Low Temperature Toughness in Bulk Nanostructured Metals, MATERIALS TRANSACTIONS, 10.2320/matertrans.MH201319, 54, 9, 1624-1628, 2013.09, Brittle-to-ductile transitions (BDT) in fine-grained Ti added ultra-low carbon steels were investigated. Temperature dependences of impact absorbed energy were measured using specimens with grain sizes of 0.4, 2, 9 and 70 mu m of which the grain sizes were controlled by heat treatments after five cycles of accumulative roll-bonding process. Although the BDT temperatures were decreased with the decrease in the grain size, the shape of BDT curves in fine-grained steels are different from those of coarse grains. Specimens with coarse grains show abrupt increase in the absorbed energy at the BDT temperature while fine-grained steels exhibit slight jump of absorbed energy at the BDT temperature and then the energy gradually increases with temperature, showing the enhancement of toughness at low temperatures in fine-grained steels. In the present paper, the characteristic BDT in fine-grained steels was discussed in terms of the thermally activated process of dislocation glide.. |
| 49. | Masaki Tanaka, Naoya Kamikawa, Nobuhiro Tsuji, Special Issue on Advanced Materials Science in Bulk Nanostructured Metals II PREFACE, MATERIALS TRANSACTIONS, 10.2320/matertrans.MPR2013906, 54, 9, 1539-1539, 2013.09. |
| 50. | Keiki Maeno, Masaki Tanaka, Kenji Higashida, Masahiro Fujikura, Kohsaku Ushioda, The brittle-to-ductile transition behaviour in Fe-Al single crystalline alloys, Advanced Materials Research, 10.4028/www.scientific.net/AMR.409.243, 409, 243-248, Vol. 409, pp.243-248, 2012.11. |
| 51. | Keiki Maeno, Masaki Tanaka, Kenji Higashida, Masahiro Fujikura, Kohsaku Ushioda, The brittle-to-ductile transition behaviour in Fe-Al single crystalline alloys, Advanced Materials Research, 10.4028/www.scientific.net/AMR.409.243, 409, 243-248, 2012.11, The morphology of deformation twinning, which influences a brittle fracture at low temperatures, was investigated in Fe-8mass%Al. Tensile tests were performed at 129K and room temperature. The specimen tested at room temperature showed yielding and kept deformed by usual slip while the specimen tested at 129K fractured in a brittle manner in an elastic regime with a number of straight markings due to deformation twinning. Detail analysis of those deformation twins suggests that the collision of deformation twinning is the initiation site of the brittle fracture. © (2012) Trans Tech Publications, Switzerland.. |
| 52. | M. Tanaka, T. Onomoto, T. Tsuchiyama, K. Higashida, Brittle to ductile transition in nickel free high nitrogen austenitic stainless steels, International Heat Treatment and Surface Engineering, 10.1179/1749514812Z.00000000029, 6, 3, 99-102, Vol.6, No.3, pp.99-102, 2012.09. |
| 53. | K. Tsujii, M. Tanaka, K. Higashida, M. Fujikura, K. Ushioda, Effect of Deformation Twinning on the Brittle-to-Ductile Transition in Fe-Al Single Crystalline Alloys., Proceedings of 4th International Conference on Fundamental Properties of Dislocations, Experimental Physics at Eötvös University and the Department of Materials Physics, pp. 41-45, 2012.09. |
| 54. | M. Tanaka, T. Onomoto, T. Tsuchiyama, K. Higashida, Brittle to ductile transition in nickel free high nitrogen austenitic stainless steels, International Heat Treatment and Surface Engineering, 10.1179/1749514812Z.00000000029, 6, 3, 99-102, 2012.09, The brittle to ductile transition (BDT) in nickel free high nitrogen austenitic stainless steel was investigated. Falling weight impact tests at 176, 273 and 336 K revealed that Fe-25Cr-1·1N (wt-%) austenitic steel exhibits a sharp BDT in spite of being a face centred cubic alloy. The plastic deformation observed following the impact tests indicated that the BDT is induced by poor ductility at low temperatures, as is the case with ferritic steels. To measure the activation energy for the BDT, the strain rate dependence of the BDT temperature was examined using four-point bending tests. The BDT temperature was found to be weakly dependent on strain rate. Arrhenius plots of the BDT temperature against strain rate showed that the activation energy for the BDT of Fe-25Cr-1·1N steel is much higher than that of low carbon ferritic steels. The origins of this distinctive BDT and the large value for its activation energy in this high nitrogen steel are discussed in terms of the reduction in dislocation mobility at low temperatures because of the interactions between the glide dislocations and the solute nitrogen atoms. © 2012 IHTSE Partnership.. |
| 55. | K. Tsujii, M. Tanaka, K. Higashida, M. Fujikura, K. Ushioda, Effect of Deformation Twinning on the Brittle-to-Ductile Transition in Fe-Al Single Crystalline Alloys., Proceedings of 4th International Conference on Fundamental Properties of Dislocations, Experimental Physics at Eötvös University and the Department of Materials Physics, 2012.09. |
| 56. | T. Shimokawa, M. Tanaka, K. Higashida, Role of Dislocation Emission from Grain Boundaries in Mechanical Properties of Bulk Nanostructured Metals, Proceedings of the International Workshop on Bulk Nanostructured Metals, pp. 27-34, 2012.06. |
| 57. | M. Tanaka, K. Higashida, T. Shimokawa, Brittle-to-ductile Transition in Bulk Nanostructured Metals, Proceedings of the International Workshop on Bulk Nanostructured Metals, pp. 15-20, 2012.06. |
| 58. | M. Tanaka, K. Higashida, T. Shimokawa, Brittle-to-ductile Transition in Bulk Nanostructured Metals, Proceedings of the International Workshop on Bulk Nanostructured Metals, 2012.06. |
| 59. | T. Shimokawa, M. Tanaka, K. Higashida, Role of Dislocation Emission from Grain Boundaries in Mechanical Properties of Bulk Nanostructured Metals, Proceedings of the International Workshop on Bulk Nanostructured Metals, 2012.06. |
| 60. | Masaki Tanaka, Tatsuro Onomoto, Toshihiro Tsuchiyama, Kenji Higashida, Brittle-to-ductile Transition in Nickel-free Austenitic Stainless Steels with High Nitrogen, ISIJ INTERNATIONAL, 10.2355/isijinternational.52.915, 52, 5, 915-921, 2012.05, The brittle-to-ductile transition (BDT) behaviour in nickel-free austenitic stainless steel with high nitrogen was investigated. Fall-weight impact tests revealed that Fe-25mass%Cr-1.1mass%N austenitic steel exhibits a sharp BDT behaviour in spite of an fcc alloy. The aspects of plastic deformation after the impact tests indicate that the BDT observed in this austenitic steel is induced by poor ductility at low temperatures as is the same as that in ferritic steels. In order to measure the activation energy for the BDT, the strain rate dependence of the BDT temperature was examined by using four-point bending tests. The weak dependence of the BDT temperature on the strain rate was observed. The Arrhenius plot of the BDT temperature against the strain rate elucidated that the activation energy for the BDT of Fe-25mass%Cr-1.1mass%N is much higher than that of low carbon ferritic steels. The origins of such distinct BDT behaviour and its large value of the activation energy in this high-nitrogen steel are discussed in terms of the reduction of dislocation mobility at low temperatures due to the interaction between glide dislocations and nitrogen solute atoms.. |
| 61. | Kenji Higashida, Masaki Tanaka, Mechanism behind Brittle-to-ductile Transition Understood by the Interaction between a Crack and Dislocations, ISIJ INTERNATIONAL, 10.2355/isijinternational.52.704, 52, 4, 704-709, 2012.04. |
| 62. | Kenji Higashida, Masaki Tanaka, Mechanism behind Brittle-to-ductile Transition Understood by the Interaction between a Crack and Dislocations, ISIJ INTERNATIONAL, 10.2355/isijinternational.52.704, 52, 4, 704-709, 2012.04, Fundamental mechanism governing the fracture toughness of materials is reviewed in terms of a concept of the interaction between a crack and dislocations. The mechanism behind brittle-to-ductile transition (BDT) is demonstrated using a simple model based on dislocation dynamics and the theory of crack-tip shielding by dislocations. The effects of dislocation mobility as well as dislocation sources on the BDT behavior are discussed, which enables us to understand the various factors such as grain refinement influencing fracture toughness.. |
| 63. | , [URL]. |
| 64. | Tomotsugu Shimokawa, Masaki Tanaka, Kenji Higashida, Effect of Grain Boundaries on Fracture Toughness in Ultrafine-Grained Metals by Atomic-scale Computational Experiments, THERMEC 2011, PTS 1-4, 10.4028/www.scientific.net/MSF.706-709.1841, 706-709, 1841-+, Vol. 706-709, pp.1841-1846, 2012.01. |
| 65. | Tomotsugu Shimokawa, Masaki Tanaka, Kenji Higashida, Effect of Grain Boundaries on Fracture Toughness in Ultrafine-Grained Metals by Atomic-scale Computational Experiments, THERMEC 2011, PTS 1-4, 10.4028/www.scientific.net/MSF.706-709.1841, 706-709, 1841-+, 2012.01, In order to investigate roles of grain boundaries on the improved fracture toughness in ultrafine-grained metals, interactions between crack tips, dislocations, and disclination dipoles at grain boundaries are performed to aluminium bicrystal models containing a crack and tilt grain boundaries using molecular dynamics simulations. A proposed mechanism to express the improved fracture toughness in ultrafine-grained metals is the disclination shielding effect on the crack tip mechanical field. The disclination shielding can be activated when a transition of dislocation sources from crack tips to grain boundaries and a transition of the grain boundary structure into a neighbouring energetically stable boundary by emitting dislocations from the grain boundary occur. The disclination shielding effect becomes large as dislocations are continuously emitted from the grain boundary without dislocation emissions from crack tips. This mechanism can further shield the mechanical field around the crack tip and obtain the plastic deformation by dislocation emissions from grain boundaries, hence it can be expected that the disclination shielding effect can improve the fracture toughness in ultrafine-grained metals. |
| 66. | S. Hata, H. Miyazaki, S. Miyazaki, M. Mitsuhara, M. Tanaka, K. Kaneko, K. Higashida, K. Ikeda, H. Nakashima, S. Matsumura, J. S. Barnard, J. H. Sharp, P. A. Midgley, High-angle triple-axis specimen holder for three-dimensional diffraction contrast imaging in transmission electron microscopy, ULTRAMICROSCOPY, 10.1016/j.ultramic.2011.03.021, 111, 8, 1168-1175, Vol.111, pp.1168-1175, 2011.07, [URL]. |
| 67. | S. Hata, H. Miyazaki, S. Miyazaki, M. Mitsuhara, M. Tanaka, K. Kaneko, K. Higashida, K. Ikeda, H. Nakashima, S. Matsumura, J. S. Barnard, J. H. Sharp, P. A. Midgley, High-angle triple-axis specimen holder for three-dimensional diffraction contrast imaging in transmission electron microscopy, ULTRAMICROSCOPY, 10.1016/j.ultramic.2011.03.021, 111, 8, 1168-1175, 2011.07, Electron tomography requires a wide angular range of specimen-tilt for a reliable three-dimensional (3D) reconstruction. Although specimen holders are commercially available for tomography, they have several limitations, including tilting capability in only one or two axes at most, e.g. tilt-rotate. For amorphous specimens, the image contrast depends on mass and thickness only and the single-tilt holder is adequate for most tomographic image acquisitions. On the other hand, for crystalline materials where image contrast is strongly dependent on diffraction conditions, current commercially available tomography holders are inadequate, because they lack tilt capability in all three orthogonal axes needed to maintain a constant diffraction condition over the whole tilt range. We have developed a high-angle triple-axis (HATA) tomography specimen holder capable of high-angle tilting for the primary horizontal axis with tilting capability in the other (orthogonal) horizontal and vertical axes. This allows the user to trim the specimen tilt to obtain the desired diffraction condition over the whole tilt range of the tomography series. To demonstrate its capabilities, we have used this triple-axis tomography holder with a dual-axis tilt series (the specimen was rotated by 90 degrees ex-situ between series) to obtain tomographic reconstructions of dislocation arrangements in plastically deformed austenitic steel foils. (C) 2011 Elsevier B.V. All rights reserved.. |
| 68. | T. Shimokawa, M. Tanaka, K. Kinoshita, K. Higashida, Roles of grain boundaries in improving fracture toughness of ultrafine-grained metals, PHYSICAL REVIEW B, 10.1103/PhysRevB.83.214113, 83, 21, Vol.83, 214113, 2011.06, [URL]. |
| 69. | Masaki Tanaka, Keiki Maeno, Kenji Higashida, Masahiro Fujikura, Kohsaku Ushioda, The Increase in a Brittle-to-ductile Transition Temperature in Fe-Al Single Crystals, ISIJ INTERNATIONAL, 10.2355/isijinternational.51.999, 51, 6, 999-1004, Vol.51, No.6, pp.999-1004, 2011.06, [URL]. |
| 70. | T. Shimokawa, M. Tanaka, K. Kinoshita, K. Higashida, Roles of grain boundaries in improving fracture toughness of ultrafine-grained metals, PHYSICAL REVIEW B, 10.1103/PhysRevB.83.214113, 83, 21, 2011.06, In order to improve the fracture toughness in ultrafine-grained metals, we investigate the interactions among crack tips, dislocations, and grain boundaries in aluminum bicrystal models containing a crack and tilt grain boundaries using molecular dynamics simulations. The results of previous computer simulations showed that grain refinement makes materials brittle if grain boundaries behave as obstacles to dislocation movement. However, it is actually well known that grain refinement increases fracture toughness of materials. Thus, the role of grain boundaries as dislocation sources should be essential to elucidate fracture phenomena in ultrafine-grained metals. A proposed mechanism to express the improved fracture toughness in ultrafine-grained metals is the disclination shielding effect on the crack tip mechanical field. Disclination shielding can be activated when two conditions are present. First, a transition of dislocation sources from crack tips to grain boundaries must occur. Second, the transformation of grain-boundary structure into a neighboring energetically stable boundary must occur as dislocations are emitted from the grain boundary. The disclination shielding effect becomes more pronounced as antishielding dislocations are continuously emitted from the grain boundary without dislocation emissions from crack tips, and then ultrafine-grained metals can sustain large plastic deformation without fracture with the drastic increase of the mobile dislocation density. Consequently, it can be expected that the disclination shielding effect can improve the fracture toughness in ultrafine-grained metals.. |
| 71. | Masaki Tanaka, Keiki Maeno, Kenji Higashida, Masahiro Fujikura, Kohsaku Ushioda, The Increase in a Brittle-to-ductile Transition Temperature in Fe-Al Single Crystals, ISIJ INTERNATIONAL, 10.2355/isijinternational.51.999, 51, 6, 999-1004, 2011.06, The effect of aluminium concentration on a brittle-to-ductile transition (BDT) has been investigated in Fe-Al single crystals. The BDT temperatures in Fe-4mass%Al and Fe-8mass%Al crystals with specimen axis were measured by an instrumental falling weight impact tester, indicating that the BDT temperature in Fe-8%Al is higher than that in Fe-4%Al. Twin-twin intersections were seen on fracture surfaces in Fe-8%Al tested at low temperatures, which shows that the intersection was the origin of a brittle fracture. In order to highlight the effect of deformation twinning on the BDT behaviour, specimens with the axis were also employed to suppress the onset of deformation twinning during the impact tests. The BDT temperature in Fe-8%Al was found to be decreased by suppressing deformation twinning, which indicates that deformation twinning is a key mechanism behind increasing the BDT temperature in Fe-Al single crystals. A model to explain the increase in the BDT temperature with aluminium content is also presented.. |
| 72. | Yoshimasa Takahashi, Junji Sakamoto, Masaki Tanaka, Kenji Higashida, Hiroshi Noguchi, Effect of hydrogen on dislocation structures around a mixed-mode fatigue crack tip in a single-crystalline iron silicon alloy, SCRIPTA MATERIALIA, 10.1016/j.scriptamat.2010.12.032, 64, 8, 721-724, Vol.64, pp.721-724, 2011.04. |
| 73. | Yoshimasa Takahashi, Junji Sakamoto, Masaki Tanaka, Kenji Higashida, Hiroshi Noguchi, Effect of hydrogen on dislocation structures around a mixed-mode fatigue crack tip in a single-crystalline iron silicon alloy, SCRIPTA MATERIALIA, 10.1016/j.scriptamat.2010.12.032, 64, 8, 721-724, 2011.04, The effect of hydrogen on dislocation structures around a mixed-mode fatigue crack tip in a single-crystalline iron silicon alloy was investigated by cross-sectional electron backscatter diffraction and high-voltage electron microscopy. In contrast to the previously reported results in an inert environment, no dislocation cells were formed around the crack tip in a hydrogen environment. The microscopic features around the crack tip suggest that hydrogen promotes a mode I-type crack growth mechanism, which reasonably explains the observed macroscopic crack growth property. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.. |
| 74. | Yoshimasa Takahashi, Keigo Yamaguchi, Masaki Tanaka, Kenji Higashida, Hiroshi Noguchi, On the micromechanism of hydrogen-assisted cracking in a single-crystalline iron-silicon alloy thin sheet, SCRIPTA MATERIALIA, 10.1016/j.scriptamat.2010.11.035, 64, 6, 537-540, Vol.64, pp.537-540, 2011.03. |
| 75. | Masaki Tanaka, Sunao Sadamatsu, Hiroto Nakamura, Kenji Higashida, The Early Stage of Dislocation Process around a Crack Tip Observed by HVEM-Tomography in Silicon Single Crystals, MATERIALS TRANSACTIONS, 10.2320/matertrans.MB201024, 52, 3, 352-357, Vol.52, No.3, pp.352-357, 2011.03, [URL]. |
| 76. | Yoshimasa Takahashi, Keigo Yamaguchi, Masaki Tanaka, Kenji Higashida, Hiroshi Noguchi, On the micromechanism of hydrogen-assisted cracking in a single-crystalline iron-silicon alloy thin sheet, SCRIPTA MATERIALIA, 10.1016/j.scriptamat.2010.11.035, 64, 6, 537-540, 2011.03, A microscopic analysis of sub-critical hydrogen-assisted cracking (HAC) in a single-crystalline iron silicon thin sheet was conducted and revealed the following points: (i) crack tip geometry and crack growth unit (striation spacing) are constant even when crack length (i.e. apparent stress intensity) and crack velocity (da/dt) significantly change; and (ii) da/dt monotonically increases with plastic zone size. These findings suggest that the effect of large-scale plasticity on the rate-limiting process should be explicitly considered in the kinetic modeling of the HAC mechanism. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.. |
| 77. | Masaki Tanaka, Sunao Sadamatsu, Hiroto Nakamura, Kenji Higashida, The Early Stage of Dislocation Process around a Crack Tip Observed by HVEM-Tomography in Silicon Single Crystals, MATERIALS TRANSACTIONS, 10.2320/matertrans.MB201024, 52, 3, 352-357, 2011.03, Crack tip dislocations in silicon single crystals were observed by combining high-voltage electron microscopy and electron tomography. Cracks were introduced by an indentation method and dislocations were introduced around the crack tip by keeping the indented sample at high temperatures for several hours. The number of dislocations emitted from the crack tip was controlled by changing the holding time of the indented specimen at high temperatures. The dislocations observed were characterized in detail. It was found that primary emitted dislocations all had the same Burgers vectors and that some dislocation segments cross-slipped around the crack. The local stress intensity factor due to dislocations was calculated, basing on the dislocation character obtained in this study, indicating that emitted dislocations shields mode I, H and III stress intensity at the crack tip. After the emission of the number of those dislocations, dislocations with another Burgers vector were emitted around the crack. It was found that those dislocations accommodate mode II and III stress components which are the excess shielding fields due lathe dislocations primary emitted from the crack tip. [doi:10.2320/matertrans.MB201024]. |
| 78. | Masaki Tanaka, Sunao Sadamatsu, Grace S. Liu, Hiroto Nakamura, Kenji Higashida, Ian M. Robertson, Sequential multiplication of dislocation sources along a crack front revealed by high-voltage electron microscopy and tomography, JOURNAL OF MATERIALS RESEARCH, 10.1557/jmr.2010.99, 26, 4, 508-513, Vol.26, No.4, pp.508-513, 2011.02, [URL]. |
| 79. | Masaki Tanaka, Sunao Sadamatsu, Grace S. Liu, Hiroto Nakamura, Kenji Higashida, Ian M. Robertson, Sequential multiplication of dislocation sources along a crack front revealed by high-voltage electron microscopy and tomography, JOURNAL OF MATERIALS RESEARCH, 10.1557/jmr.2010.99, 26, 4, 508-513, 2011.02, The three-dimensional structure of crack tip dislocations in single crystal silicon was observed by combining high-voltage electron microscopy and tomography. It was revealed that dislocations cross-slipped proximal to the crack tip even in the initial stages of plastic deformation. The local stress intensity factor along the crack front was calculated by taking into account the experimentally determined dislocation character. Based on these observations and calculations, a model to account for the sequential multiplication of dislocation sources along the crack front is proposed.. |
| 80. | Yoshimasa Takahashi, Junji Sakamoto, Masaki Tanaka, Kenji Higashida, Hiroshi Noguchi, Characterization of dislocation structures around a mixed-mode fatigue crack tip in a single-crystalline iron-silicon alloy, SCRIPTA MATERIALIA, 10.1016/j.scriptamat.2010.09.033, 64, 2, 157-160, Vol.64, pp.157-160, 2011.01. |
| 81. | K. Edalati, H. Iwaoka, Z. Horita, M. Tanaka, K. Higashida, H. Fujiwara, K. Ameyama, Fabrication of ultrafine-grained Ti-(5-50wt.%)Al2O3 composites using high-pressure torsion, KOVOVE MATERIALY-METALLIC MATERIALS, 10.4149/km_2011_1_85, 49, 1, 85-92, Vol. 49, No.1, pp.85-91, 2011.01. |
| 82. | Yoshimasa Takahashi, Junji Sakamoto, Masaki Tanaka, Kenji Higashida, Hiroshi Noguchi, Characterization of dislocation structures around a mixed-mode fatigue crack tip in a single-crystalline iron-silicon alloy, SCRIPTA MATERIALIA, 10.1016/j.scriptamat.2010.09.033, 64, 2, 157-160, 2011.01, Dislocation structures around a mixed-mode fatigue crack tip introduced into a single-crystalline iron silicon alloy is characterized by cross-sectional electron backscatter diffraction and high-voltage electron microscopy. The results show that the crack growth is preceded by the formation of a cell band and the crack grows along cell boundaries. Crack growth rate and width of the cell band are constant despite the monotonic increase in stress intensity, which is anomalous in terms of the conventional fracture mechanics concept. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.. |
| 83. | K. Edalati, H. Iwaoka, Z. Horita, M. Tanaka, K. Higashida, H. Fujiwara, K. Ameyama, Fabrication of ultrafine-grained Ti-(5-50wt.%)Al2O3 composites using high-pressure torsion, KOVOVE MATERIALY-METALLIC MATERIALS, 10.4149/km_2011_1_85, 49, 1, 85-92, 2011.01, Ti-matrix composites reinforced with Al2O3 fractions of up to 50 wt.% were fabricated by cold consolidation of powder mixtures using high-pressure torsion (HPT). The grain size of the Ti matrix was reduced to similar to 100 nm. A relative density greater than similar to 99 % was attained for composites containing up to 30 % Al2O3 following the rule of mixture. The Vickers microhardness increased with an increase in the Al2O3 fraction but the bending stress and ductility decreased. The HPT-processed composites exhibited an abrupt increase in the hardness when they were annealed at 800-900 K, indicating a successful achievement of consolidation.. |
| 84. | Masaki Tanaka, Grace S. Liu, Tomonobu Kishida, Kenji Higashida, Ian M. Robertson, Transition from a punched-out dislocation to a slip dislocation revealed by electron tomography, JOURNAL OF MATERIALS RESEARCH, 10.1557/JMR.2010.0308, 25, 12, 2292-2296, Vol.25, pp.2292-2296, 2010.12, [URL]. |
| 85. | Masaki Tanaka, Grace S. Liu, Tomonobu Kishida, Kenji Higashida, Ian M. Robertson, Transition from a punched-out dislocation to a slip dislocation revealed by electron tomography, JOURNAL OF MATERIALS RESEARCH, 10.1557/JMR.2010.0308, 25, 12, 2292-2296, 2010.12, Punched-out dislocations emitted from an octahedral oxide precipitate in single-crystal silicon were investigated using high-voltage electron microscopy and tomography (HVEM-tomography) to understand the mechanism of softening caused by the oxide precipitates In the present paper, direct evidence of the transition of a punched-out prismatic dislocation loop to a slip dislocation is presented The punched-out dislocation grows into a large matrix dislocation loop by absorption of interstitial atoms, which were produced during oxide precipitation. |
| 86. | Masaki Tanaka, Kenji Higashida, Tomotsugu Shimokawa, The effect of severe plastic deformation on the brittle-ductile transition in low carbon steel, Materials Science Forum, 10.4028/www.scientific.net/MSF.633-634.471, 633-634, 471-480, Vol. 633-634, pp. 471-480, 2010.11. |
| 87. | Masaki Tanaka, Kenji Higashida, Tomotsugu Shimokawa, The effect of severe plastic deformation on the brittle-ductile transition in low carbon steel, Materials Science Forum, 10.4028/www.scientific.net/MSF.633-634.471, 633-634, 471-480, 2010.11, Brittle-ductile transition (BDT) behaviour was investigated in low carbon steel deformed by an accumulative roll-bonding (ARB) process. The temperature dependence of its fracture toughness was measured by conducting four-point bending tests at various temperatures and strain rates. The fracture toughness increased while the BDT temperature decreased in the specimens deformed by the ARB process. Arrhenius plots between the BDT temperatures and the strain rates indicated that the activation energy for the controlling process of the BDT was not changed by the deformation with the ARB process. It was deduced that the decrease in the BDT temperature by grain refining was not due to the increase in the dislocation mobility controlled by short-range barriers. Quasi-three-dimensional simulations of dislocation dynamics, taking into account of crack tip shielding due to dislocations, were performed to investigate the effect of a dislocation source spacing along a crack front on the BDT. The simulation indicated that the BDT temperature is decreased with decreasing in the dislocation source spacing. Molecular dynamics simulations revealed that moving dislocations were impinged against grain boundaries and were reemitted from there with increasing strain. It indicates that grain boundaries can be new sources in ultra-fine grained materials, which increases toughness at low temperatures. © (2010) Trans Tech Publications.. |
| 88. | Masaki Tanaka, Kenji Higashida, Sunao Sadamatsu, Hiroto Nakamura, CRACK TIP DISLOCATIONS OBSERVED BY ELECTRON TOMOGRAPHY IN SINGLE CRYSTAL SILICON, CHALLENGES IN MATERIALS SCIENCE AND POSSIBILITIES IN 3D AND 4D CHARACTERIZATION TECHNIQUES, 443-448, (2010), p.443-448., 2010.10. |
| 89. | Yoshimasa Takahashi, Masaki Tanaka, Kenji Higashida, Kazuhiro Yasuda, Syo Matsumura, Hiroshi Noguchi, A combined environmental straining specimen holder for high-voltage electron microscopy, ULTRAMICROSCOPY, 10.1016/j.ultramic.2010.07.011, 110, 11, 1420-1427, Vol.110, pp.1420-1427., 2010.10. |
| 90. | Yoshimasa Takahashi, Masaki Tanaka, Kenji Higashida, Kazuhiro Yasuda, Syo Matsumura, Hiroshi Noguchi, A combined environmental straining specimen holder for high-voltage electron microscopy, ULTRAMICROSCOPY, 10.1016/j.ultramic.2010.07.011, 110, 11, 1420-1427, 2010.10, A novel specimen holder that enables in situ observation of crack-tip deformation and/or fracture under a controlled environment is developed for a high-voltage electron microscope (HVEM). A window-type environmental cell (EC) that incorporates a uniaxial straining apparatus is built into a side-entry-type single-tilt specimen holder. The gas control in EC, straining apparatus design, limited field of view for crack-tip observation, and specimen preparation for the specimen holder are presented in detail. Experimental results successfully demonstrate that the developed specimen holder is quite useful for the dynamic observation of crack-tip deformation and/or fracture subjected to a hostile environment, such as hydrogen gas. (C) 2010 Elsevier B.V. All rights reserved.. |
| 91. | Masaki Tanaka, Kenji Higashida, Sunao Sadamatsu, Hiroto Nakamura, CRACK TIP DISLOCATIONS OBSERVED BY ELECTRON TOMOGRAPHY IN SINGLE CRYSTAL SILICON, CHALLENGES IN MATERIALS SCIENCE AND POSSIBILITIES IN 3D AND 4D CHARACTERIZATION TECHNIQUES, 443-448, 2010.10, Three-dimensional structures of crack tip dislocations in silicon crystals have been examined by combining scanning transmission electron microscopy and computed tomography. Cracks were introduced by a Vickers hardness tester at room temperature and the sample was heated at 823K for one hour in order to introduce dislocations around the crack tips. Dislocation segments cut out from loops were observed around the crack tip, the three-dimensional structure of which was characterised by using by electron tomography. Their Burgers vectors including the signs were also determined by oscillating contrasts along dislocations. In order to investigate the effect of the dislocations on fracture behaviours, local stress intensity factor due to one dislocation was calculated.. |
| 92. | Youn-Jeong Hong, Masaki Tanaka, Kenji Higashida, The Effect of Oxygen on the Brittle-to-Ductile Transition in Silicon Single Crystals, PRICM 7, PTS 1-3, 10.4028/www.scientific.net/MSF.654-656.1299, 654-656, 1299-1302, Vol.654-656, pp.1299-1302, 2010.08. |
| 93. | Y.-J. Hong, M. Tanaka, K. Maeno, K. Higashida, The effect of dopants on the brittle-to-ductile transition in silicon crystals, Journal of Physics: Conference Series, Vol.240, p.012141, 2010.08. |
| 94. | Masaki Tanaka, Masaki Honda, Sunao Sadamatsu, Kenji Higashida, 3-D structures of crack-tip dislocations and their shielding effect revealed by electron tomography, JOURNAL OF ELECTRON MICROSCOPY, 10.1093/jmicro/dfq031, 59, SUPPL. 1, S55-S60, Vol.59, pp.S55-S60, 2010.08. |
| 95. | Effect of gaseous hydrogen on cyclic slip behavior around a stage i fatigue crack tip in an iron alloy. |
| 96. | Masaki Tanaka, Masaki Honda, Sunao Sadamatsu, Kenji Higashida, 3-D structures of crack-tip dislocations and their shielding effect revealed by electron tomography, JOURNAL OF ELECTRON MICROSCOPY, 10.1093/jmicro/dfq031, 59, SUPPL. 1, S55-S60, 2010.08, Three-dimensional structures of crack-tip dislocations in silicon crystals have been examined by combining scanning transmission electron microscopy and computed tomography. Cracks were introduced by a Vickers hardness tester at room temperature, and the sample was heated at 823 K for 1 h in order to introduce dislocations around the crack tips. Dislocation segments cut out from loops were observed around the crack tip, the three-dimensional structure of which was characterized by using by electron tomography. Their Burgers vectors including the sings were also determined by oscillating contrasts along dislocations. In order to investigate the effect of the dislocations on fracture behaviours, local stress intensity factor due to one dislocation was calculated, which indicates the dislocations observed were shielding type to increase fracture toughness.. |
| 97. | Effect of gaseous hydrogen on cyclic slip behavior around a stage i fatigue crack tip in an iron alloy. |
| 98. | Youn-Jeong Hong, Masaki Tanaka, Kenji Higashida, The Effect of Oxygen on the Brittle-to-Ductile Transition in Silicon Single Crystals, PRICM 7, PTS 1-3, 10.4028/www.scientific.net/MSF.654-656.1299, 654-656, 1299-1302, 2010.08, The brittle-to-ductile transition (BDT) in Czochralski (CZ) grown silicon single crystals and floating-zone (FZ) grown silicon single crystals was investigated by three-point bending. The temperature dependence of the apparent fracture toughness was measured in three different cross-head speeds. It was found that the BDT temperature in the CZ silicon crystal was higher than that in FZ silicon crystal, suggesting that the solute oxygen decreases dislocation mobility. However, the activation energies obtained from the strain rate dependence of the BDT temperatures were nearly the same in both the CZ and FZ silicon crystals, indicating that the dislocation mobility is not influenced by the solute oxygen. In this paper, the origin of the difference in the BDT temperature is discussed, focusing the role of the solute oxygen on the dislocation glide.. |
| 99. | Youn Jeong Hong, Masaki Tanaka, Keiki Maeno, Kenji Higashida, The effect of dopants on the brittle-to-ductile transition in silicon single crystals, 15TH INTERNATIONAL CONFERENCE ON THE STRENGTH OF MATERIALS (ICSMA-15), 10.1088/1742-6596/240/1/012141, 240, 1299-1302, 2010.08, The brittle-to-ductile transition (BDT) in boron, antimony and arsenic doped Cz silicon crystals has been experimentally studied, respectively. The BDT temperatures in antimony and arsenic doped silicon wafers are lower than that in a non-doped wafer while the BDT temperature in a boron doped wafer is almost the same as that in the non-doped wafer. The activation energy was obtained from the strain rate dependence of the BDT temperature. It was found that the values of the activation energy in the antimony and arsenic doped wafers are lower than that in the non-doped and boron doped wafers, indicating that the dislocation velocity in the antimony and arsenic doped silicon is faster than that in the non-doped while the dislocation velocity in the boron doped is the same as that in the non-doped. The effect of increasing in dislocation velocity on the BDT temperature was calculated by two-dimensional discrete dislocation dynamics simulations, indicating that the increasing in dislocation velocity decreases the BDT temperature in silicon single crystals.. |
| 100. | Masaki Tanaka, Keiki Maeno, Kenji Higashida, The Effect of Boron/Antimony on the Brittle-to-Ductile Transition in Silicon Single Crystals, MATERIALS TRANSACTIONS, 10.2320/matertrans.M2010048, 51, 7, 1206-1209, Vol.51, No.7, pp.1206-1029, 2010.07, [URL]. |
| 101. | Masaki Tanaka, Keiki Maeno, Kenji Higashida, The Effect of Boron/Antimony on the Brittle-to-Ductile Transition in Silicon Single Crystals, MATERIALS TRANSACTIONS, 10.2320/matertrans.M2010048, 51, 7, 1206-1209, 2010.07, The brittle-to-ductile transition (BDT) in boron or antimony doped Czochralski (CZ) silicon single crystals was investigated by three-point bending. The temperature dependence of the apparent fracture toughness was measured in three different crosshead speeds, indicating that the BDT temperature in boron doped silicon is the same as that in non-doped one while the BDT temperature in antimony doped silicon is lower than that in non-doped one. The activation energy was obtained from the deformation rate dependence of the BDT temperature, suggesting that the dislocation velocity in boron doped silicon is the same as that in non-doped while the dislocation velocity in antimony doped is larger than that in non-doped one. [doi:10.2320/matertrans.M2010048]. |
| 102. | Kenji Higashida, Masaki Tanaka, Sunao Sadamatsu, Characterization of Crack-tip Dislocations and Their Effects on Materials Fracture, PRICM 7, PTS 1-3, 10.4028/www.scientific.net/MSF.654-656.2307, 654-656, 2307-2311, Vol.654-656, pp.2307-2311, 2010.06. |
| 103. | Kaveh Edalati, Zenji Horita, Hiroshi Fujiwara, Kei Ameyama, Masaki Tanaka, Kenji Higashida, High Strength and Ductility in Ball-Milled Titanium Powders Consolidated by High-Pressure Torsion, PRICM 7, PTS 1-3, 10.4028/www.scientific.net/MSF.654-656.1239, 654-656, 1239-+, Vol.654-656, pp.1239-1242, 2010.06. |
| 104. | Kaveh Edalati, Zenji Horita, Masaki Tanaka, Kenji Higashida, High Pressure Torsion of Pure Ti: Effect of Pressure and Strain on Allotropy, THERMEC 2009 SUPPLEMENT, 10.4028/www.scientific.net/AMR.89-91.171, 89-91, 171-+, 2010.06. |
| 105. | Kenji Higashida, Masaki Tanaka, Sunao Sadamatsu, Characterization of Crack-tip Dislocations and Their Effects on Materials Fracture, PRICM 7, PTS 1-3, 10.4028/www.scientific.net/MSF.654-656.2307, 654-656, 2307-2311, 2010.06, Three-dimensional structure of crack tip dislocations were investigated by combining scanning transmission electron microscopy (STEM) and electron tomography (ET) in silicon single crystals. P-type (001) silicon single crystals were employed. cracks were introduced from an indent on the (001) surface. The specimen was heated at 873K in order to introduce dislocations at the crack tips. The specimen was thinned to include the crack tip in the foil by an iron milling machine. STEM-ET observation revealed the three-dimensional structure of crack tip dislocations. Their Burgers vectors were determined by using an invisibility criterion. The local stress intensity factor was calculated using the dislocation characters obtained in the observation in this study, indicating that the dislocations observed were mode II shielding type dislocations.. |
| 106. | Kaveh Edalati, Zenji Horita, Masaki Tanaka, Kenji Higashida, High Pressure Torsion of Pure Ti: Effect of Pressure and Strain on Allotropy, THERMEC 2009 SUPPLEMENT, 10.4028/www.scientific.net/AMR.89-91.171, 89-91, 171-+, 2010.06, High-pressure torsion (HPT) was conducted on commercial grade pure titanium (99.4%) by applying pressures in a wide range from 1.2 to 40 GPa. When the microhardness was plotted against equivalent strain, the hardness saturates to a constant level at each applied pressure. Such a level at the saturation depends on the applied pressure: for up to the pressure of 4 GPa, the saturation level is independent of the pressure but, for the pressures above 4 GPa, the hardness gradually increases with pressure because of the formation of an omega phase. Bending tests showed that an excellent ductility as well as high bending strength was achieved for the sample processed at 2 GPa. The bending ductility was reduced for the sample at 6 GPa because of the w phase formation.. |
| 107. | Kaveh Edalati, Zenji Horita, Hiroshi Fujiwara, Kei Ameyama, Masaki Tanaka, Kenji Higashida, High Strength and Ductility in Ball-Milled Titanium Powders Consolidated by High-Pressure Torsion, PRICM 7, PTS 1-3, 10.4028/www.scientific.net/MSF.654-656.1239, 654-656, 1239-+, 2010.06, Pure Ti powders were subjected to ball milling and subsequently high-pressure torsion (HPT) for consolidation. It is found that a fully dense (99.9%) disc with ultrafine grained structure (similar to 50-300 nm) was produced. The strength and ductility were well comparable to those of ball-milled Ti-6%Al-4%V powders after hot roll sintering.. |
| 108. | Y. Takahashi, M. Tanaka, K. Higashida, K. Yamaguchi, H. Noguchi, An intrinsic effect of hydrogen on cyclic slip deformation around a {110} fatigue crack in Fe-3.2 wt.% Si alloy, ACTA MATERIALIA, 10.1016/j.actamat.2009.11.040, 58, 6, 1972-1981, Vol.58, pp.1972-1981, 2010.04. |
| 109. | Y. Takahashi, M. Tanaka, K. Higashida, K. Yamaguchi, H. Noguchi, An intrinsic effect of hydrogen on cyclic slip deformation around a {110} fatigue crack in Fe-3.2 wt.% Si alloy, ACTA MATERIALIA, 10.1016/j.actamat.2009.11.040, 58, 6, 1972-1981, 2010.04, The effect of gaseous hydrogen on cyclic slip behavior around a fatigue crack tip introduced along the {1 1 0} plane in a Fe-3.2 wt.% Si alloy is precisely investigated by cross-sectional transmission electron microscopy and fractography. The results clearly suggest that the fatigue crack growth rate is promoted by hydrogen, whereas the number of dislocations emitted per load cycle is reduced. In addition, dislocation distribution is localized around the crack, causing quasi-brittle crack morphology. A sustained load test confirms that no subcritical crack growth caused by cleavage or micro-void coalescence exists along the {1 1 0} plane, which indicates that the observed increase in the fatigue crack growth rate is correlated solely to the intrinsic effect of hydrogen on the cyclic slip-off process around the crack tip. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.. |
| 110. | M. Tanaka, K. Higashida and T. Shimokawa, The brittle-to-ductile transition in severely deformed low carbon steel, Supplemental Progeedings, Vol.2, TMS, 787-794, 2010.02. |
| 111. | Masaki Tanaka, Kenji Higashida, Tomotsugu Shimokawa, The brittle-to-ductile transition in severely deformed low carbon steel, TMS 2010 139TH ANNUAL MEETING & EXHIBITION - SUPPLEMENTAL PROCEEDINGS, VOL 2: MATERIALS CHARACTERIZATION, COMPUTATION AND MODELING AND ENERGY, 2, 787-+, 2010.02, The brittle-to-ductile transition (BDT) behaviour was investigated in low carbon steel deformed by an accumulative roll-bonding (ARB) process. The temperature dependence of its fracture toughness was measured by conducting four-point bending tests at various strain rates. The fracture toughness increased while the BDT temperature decreased in the specimens deformed by the ARB process. Arrhenius plots between the BDT temperatures and the strain rates indicated that the activation energy for the BDT did not change due to the deformation with the ARB process. It indicated that the decrease in the BDT temperature by grain refining was not clue to the reduction in the dislocation mobility with respect to short-range barriers. Quasi-three-dimensional simulations of discrete dislocation dynamics indicated that the decrease in the number of dislocation sources decreases in the BDT temperature. The roles of grain boundaries will be also discussed in order to explain the decrease in the BDT temperature.. |
| 112. | S. Sadamatsu, M. Tanaka, K. Higashida, K. Kaneko, M. Mitsuhara, S. Hata, M. Honda, Crack tip dislocations observed by combining scanning transmission electron microscopy and computed tomography, THERMEC 2009 SUPPLEMENT, 10.4028/www.scientific.net/AMR.89-91.473, 89-91, 473-+, Vol.89-91, pp.473-478, 2010.01. |
| 113. | K. Edalati, Z. Horita, M. Tanaka and K. Higashida, High pressure torsion of pure Ti: Effect of pressure and strain on allotropy, Advanced Materials Research, Vol.89-91, pp.171-176, 2010.01. |
| 114. | Sunao Sadamatsu, Masaki Tanaka, Masaki Honda, Kenji Higashida, Crack tip dislocations observed by TEM-tomography in silicon single crystals, 15TH INTERNATIONAL CONFERENCE ON THE STRENGTH OF MATERIALS (ICSMA-15), 10.1088/1742-6596/240/1/012142, 240, Vol.240, p.012142, 2010.01. |
| 115. | S. Sadamatsu, M. Tanaka, K. Higashida, K. Kaneko, M. Mitsuhara, S. Hata, M. Honda, Crack tip dislocations observed by combining scanning transmission electron microscopy and computed tomography, THERMEC 2009 SUPPLEMENT, 10.4028/www.scientific.net/AMR.89-91.473, 89-91, 473-+, 2010.01, Crack tip dislocations and dislocations introduced by three point-bending tests at high temperature are observed by combinating scanning transmission electron microscopy and computed tomography (STEM-CT). Commercially available P type (001) single crystal silicon wafers were employed. A series of STEM image was acquired from -60 degrees to +60 degrees in tilt range with 2 degrees in tilt step. The diffraction vector was maintained close to g(hkl) = 220 during the acquisition by adjusting the [110] direction of the sample parallel to the tilt axis of the holder. Reconstructed images of dislocations revealed dislocation structures in three-dimension.. |
| 116. | Sunao Sadamatsu, Masaki Tanaka, Masaki Honda, Kenji Higashida, Crack tip dislocations observed by TEM-tomography in silicon single crystals, 15TH INTERNATIONAL CONFERENCE ON THE STRENGTH OF MATERIALS (ICSMA-15), 10.1088/1742-6596/240/1/012142, 240, 2010.01, 3D observations of dislocations at a crack tip were attempted by transmission electron microscopy and computed tomography in order to reveal the 3D structure of dislocations emitted around a crack tip. {011} cracks were introduced into a (001) silicon single crystal wafer by using an indentation method at room temperature. The specimens indented were heated and kept at high temperatures to introduce dislocations from the crack tip. The specimen holder was tilted +/-31 degrees by 2 degrees step and dislocation images were taken at every step. The diffraction vector was kept nearly 220 during the tilting operation. The Burgers vectors of the dislocation segments were determined, which included the signs of Burgers vectors. The dislocations observed here were those which accommodate mode II stress intensity around the crack tip. 3D observations using electron tomography reveal these complex crucial processes around the crack tip, which should contribute to understanding the dislocation process improving fracture toughness of crystalline materials.. |
| 117. | M. Tanaka, K. Higashida and T. Shimokawa, The role of dislocation sources on the brittle-ductile transition, Proceedings of the 2nd International Symposium on Steel Science (ISSS2009), 285-287, 2009.10. |
| 118. | M. Tanaka, K. Higashida and T. Shimokawa, The role of dislocation sources on the brittle-ductile transition, Proceedings of the 2nd International Symposium on Steel Science (ISSS2009), 2009.10. |
| 119. | Youn-Jeong Hong, Masaki Tanaka, Kenji Higashida, The Effect of Arsenic on the Brittle-to-Ductile Transition in Si Single Crystals, MATERIALS TRANSACTIONS, 10.2320/matertrans.MAW200919, 50, 9, 2177-2181, Vo.50, pp.2177-2181, 2009.09, [URL]. |
| 120. | Youn-Jeong Hong, Masaki Tanaka, Kenji Higashida, The Effect of Arsenic on the Brittle-to-Ductile Transition in Si Single Crystals, MATERIALS TRANSACTIONS, 10.2320/matertrans.MAW200919, 50, 9, 2177-2181, 2009.09, The brittle-to-ductile transition (BDT) in arsenic doped (001) CZ silicon single crystals has been experimentally studied. The temperature dependence of apparent fracture toughness was measured by three-point bending tests at various strain rates. The BDT temperature in arsenic doped silicon was found to be lower than that in non-doped. The activation energy was obtained from the strain rate dependence of the BDT temperature. It was found that the value of the activation energy in the arsenic doped silicon is lower than that in non-doped, suggesting that the dislocation velocity in the silicon single crystal was increased by arsenic doping. The effect of increasing in dislocation velocity on the BDT temperature was also investigated by two-dimensional discrete dislocation dynamics simulations, indicating that the BDT temperature is decreased by increasing in dislocation velocity. [doi:10.2320/matertrans.MAW200919]. |
| 121. | Yoshimasa Takahashi, Masaki Tanaka, Kenji Higashida, Hiroshi Noguchi, Hydrogen-induced slip localization around a quasi-brittle fatigue crack observed by high-voltage electron microscopy, SCRIPTA MATERIALIA, 10.1016/j.scriptamat.2009.03.020, 61, 2, 145-148, Vol.61, No.2, pp.145-148, 2009.07, [URL]. |
| 122. | Yoshimasa Takahashi, Masaki Tanaka, Kenji Higashida, Hiroshi Noguchi, Hydrogen-induced slip localization around a quasi-brittle fatigue crack observed by high-voltage electron microscopy, SCRIPTA MATERIALIA, 10.1016/j.scriptamat.2009.03.020, 61, 2, 145-148, 2009.07, The effect of hydrogen on cyclic slip behavior around a fatigue crack tip in a bulk Fe-Si alloy is successfully observed by high-voltage electron microscopy. The observation explicitly reveals the following points: (i) hydrogen reduces the amount of cyclic slip whereas it promotes crack growth rate; and (ii) hydrogen induces a quasi-brittle crack growth that accompanies localized slip in the crack periphery. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.. |
| 123. | Yoshimasa Takahashi, Masaki Tanaka, Kenji Higashida, Hiroshi Noguchi, High-voltage electron-microscopic observation of cyclic slip behavior around a fatigue crack tip in an iron alloy, SCRIPTA MATERIALIA, 10.1016/j.scriptamat.2009.01.002, 60, 8, 717-720, Vol.40, No.8, pp.717-720, 2009.04, [URL]. |
| 124. | Yoshimasa Takahashi, Masaki Tanaka, Kenji Higashida, Hiroshi Noguchi, High-voltage electron-microscopic observation of cyclic slip behavior around a fatigue crack tip in an iron alloy, SCRIPTA MATERIALIA, 10.1016/j.scriptamat.2009.01.002, 60, 8, 717-720, 2009.04, The cyclic slip behavior around a fatigue crack tip originally located inside a bulk Fe-Si alloy was successfully observed by a high-voltage electron microscope in combination with a novel specimen preparation method. The method, by taking advantages of ion milling and focused ion beam techniques, ensures that the original shape of the crack tip is preserved without introducing additional slips. The observation confirms that the slip bands emitted from the fatigue crack tip are bounded by a labyrinth-like wall structure. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.. |
| 125. | Masaki Tanaka, Kenji Higashida, Tomotsugu Shimokawa, Tatsuya Morikawa, Brittle-Ductile Transition in Low Carbon Steel Deformed by the Accumulative Roll Bonding Process, MATERIALS TRANSACTIONS, 10.2320/matertrans.MD200817, 50, 1, 56-63, Vol.50, No.1, pp.56-63, 2009.01, [URL]. |
| 126. | Yoshimasa Takahashi, Masaki Tanaka, Kenji Higashida, Hiroshi Noguchi, Effect of hydrogen on microscopic deformation process near Stage II fatigue crack tip, EFFECTS OF HYDROGEN ON MATERIALS, 203-+, 2009.01. |
| 127. | Microscopic study on the effect of hydrogen on fatigue crack growth process in a chromium-molybdenum steel. |
| 128. | Microscopic study on the effect of hydrogen on deformation process near stage II fatigue crack tip. |
| 129. | Masaki Tanaka, Kenji Higashida, Tomotsugu Shimokawa, Tatsuya Morikawa, Brittle-Ductile Transition in Low Carbon Steel Deformed by the Accumulative Roll Bonding Process, MATERIALS TRANSACTIONS, 10.2320/matertrans.MD200817, 50, 1, 56-63, 2009.01, Brittle-ductile transition (BDT) behaviour was investigated in low carbon steel deformed by an accumulative roll-bonding (ARB) process. The temperature dependence of its fracture toughness was measured by conducting four-point bending tests at various temperatures and strain rates. The fracture toughness increased while the BDT temperature decreased in the specimens deformed by the ARB process. Arrhenius plots between the BDT temperatures and the strain rates indicated that the activation energy for the BDT did not change due to the deformation with the ARB process. It was deduced that the decrease in the BDT temperature by grain refining was not due to the increase in the dislocation mobility controlled by short-range obstacles. Molecular dynamics simulations revealed that moving dislocations were impinged against grain boundaries, creating a shielding field, and were reemitted from there with increasing strain. Grain refining led to an increase in the fracture toughness at low temperatures and a decrease in the BDT temperature. In the present paper, the roles of-rain boundaries have been discussed in order to explain the enhancement in the fracture toughness of fine-grained materials at low temperatures, and the decrease in the BDT temperature. [doi:10.2320/matertrans.MD200817]. |
| 130. | Yoshimasa Takahashi, Masaki Tanaka, Kenji Higashida, Hiroshi Noguchi, Effect of hydrogen on microscopic deformation process near Stage II fatigue crack tip, EFFECTS OF HYDROGEN ON MATERIALS, 203-+, 2009.01. |
| 131. | Microscopic study on the effect of hydrogen on fatigue crack growth process in a chromium-molybdenum steel. |
| 132. | Microscopic study on the effect of hydrogen on deformation process near stage II fatigue crack tip. |
| 133. | Three-Dimensional Observation of Dislocations by Electron Tomography in a Silicon Crystal (vol 49, pg 1953, 2008). |
| 134. | Three-Dimensional Observation of Dislocations by Electron Tomography in a Silicon Crystal (vol 49, pg 1953, 2008). |
| 135. | Masaki Tanaka, Kenji Higashida, Kenji Kaneko, Satoshi Hata, Masatoshi Mitsuhara, Crack tip dislocations revealed by electron tomography in silicon single crystal, SCRIPTA MATERIALIA, 10.1016/j.scriptamat.2008.06.042, 59, 8, 901-902, Vol.59, No.8, pp.901-904, 2008.10, [URL]. |
| 136. | M. Tanaka, E. Tarleton, S. G. Roberts, The brittle-ductile transition in single-crystal iron, ACTA MATERIALIA, 10.1016/j.actamat.2008.06.025, 56, 18, 5123-5129, Vol.56, No.18, pp.5123-5129, 2008.10, [URL]. |
| 137. | Masaki Tanaka, Kenji Higashida, Kenji Kaneko, Satoshi Hata, Masatoshi Mitsuhara, Crack tip dislocations revealed by electron tomography in silicon single crystal, SCRIPTA MATERIALIA, 10.1016/j.scriptamat.2008.06.042, 59, 8, 901-902, 2008.10, Crack tip dislocations in silicon single crystals have been observed by a combination of annular dark-field scanning transmission electron microscopy and computed tomography. A series of images was acquired by maintaining the diffraction vector parallel to that of crack propagation to achieve sharp images of the dislocations. The observed dislocations were reconstructed by a filtered back-projection, and exhibited three-dimensional configurations of overlaid dislocations around the crack tip. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.. |
| 138. | M. Tanaka, E. Tarleton, S. G. Roberts, The brittle-ductile transition in single-crystal iron, ACTA MATERIALIA, 10.1016/j.actamat.2008.06.025, 56, 18, 5123-5129, 2008.10, The fracture behaviour of single-crystal pure iron was studied by four-point bending of pre-cracked specimens at temperatures between 77 and 180 K and strain rates between 4.46 x 10(-5) and 4.46 x 10(-3) s(-1). Fracture behaviour changes from brittle to ductile with increasing temperature. The brittle-ductile transition (BDT) temperature increases with increasing strain rate. The relation between BDT temperature and strain rate follows an Arrhenius relation, giving an activation energy for the BDT of 0.33 eV. Dislocation-dynamics simulations of the crack-tip plasticity and resultant shielding of the crack tip were performed using two different variants of the dislocation velocity/stress/temperature relation. The models predict an explicit BDT, and give a good quantitative fit to the experimental transition temperatures. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.. |
| 139. | Masaki Tanaka, Masaki Honda, Masatoshi Mitsuhara, Satoshi Hata, Kenji Kaneko, Kenji Higashida, Three-Dimensional Observation of Dislocations by Electron Tomography in a Silicon Crystal, MATERIALS TRANSACTIONS, 10.2320/matertrans.MAW200828, 49, 9, 1953-1956, Vol.49, No.9, pp.1953-1956, 2008.09, [URL]. |
| 140. | M. Tanaka, A.J. Wilkinson, S.G. Roberts, Ductile-brittle transition of poly-crystalline iron and iron-chromium alloys, J. Nucl. Mater., Vol.378, No.3, pp.305-311, 2008.09, [URL]. |
| 141. | Yoshimasa Takahashi, Tanaka Masaki, Kenji Higashida, Hiroshi Noguchi, Effect of hydrogen on microscopic deformation process near stage II fatigue crack tip., Effects of Hydrogen on Materials, pp.203-210, 2008.09. |
| 142. | Masaki Tanaka, Angus J. Wilkinson, Steve G. Roberts, Ductile-brittle transition of polycrystalline iron and iron-chromium alloys, JOURNAL OF NUCLEAR MATERIALS, 10.1016/j.jnucmat.2008.06.039, 378, 3, 305-311, 2008.09. |
| 143. | Masaki Tanaka, Angus J. Wilkinson, Steve G. Roberts, Ductile-brittle transition of polycrystalline iron and iron-chromium alloys, JOURNAL OF NUCLEAR MATERIALS, 10.1016/j.jnucmat.2008.06.039, 378, 3, 305-311, 2008.09, Fracture toughness of polycrystalline Fe, Fe-3%Cr and Fe-9%Cr was measured by four-point bending of pre-cracked specimens at temperatures between 77 K and 150 K and strain rates between 4.46 x 10(-4) and 2.23 x 10(-2) s(-1). For all materials, fracture behaviour changed with increasing temperature from brittle to ductile at a distinct brittle-ductile transition temperature (T-c), which increased with increasing strain rate. At low strain rates, an Arrhenius relation was found between T-c and strain rate in each material. At high strain rates, T-c was at slightly higher values than those expected from extrapolation of the Arrhenius relation from lower strain rates. This shift of T-c was associated with twinning near the crack tip. For each material, use of an Arrhenius relation for tests at strain rates at which specimens showed twinning gave the same activation energy as for the low strain Fate tests. The values of activation energy for the brittle-ductile transition of polycrystalline Fe, Fe-3%Cr and Fe-9%Cr were found to be 0.21, 0.15 and 0.10eV, respectively, indicating that the activation energy for dislocation glide decreases with increasing chromium concentration in iron. (c) 2008 Elsevier B.V. All rights reserved.. |
| 144. | Masaki Tanaka, Masaki Honda, Masatoshi Mitsuhara, Satoshi Hata, Kenji Kaneko, Kenji Higashida, Three-Dimensional Observation of Dislocations by Electron Tomography in a Silicon Crystal, MATERIALS TRANSACTIONS, 10.2320/matertrans.MAW200828, 49, 9, 1953-1956, 2008.09, Dislocations in a silicon single crystal introduced by three point-bending at a high temperature were observed by electron tomography in annular dark field-scanning transmission electron microscopy (ADF-STEM). Commercially available P type (001) single crystal wafers were employed. An ADF STEM tilt series was acquired from -60 degrees to +60 degrees in tilt range with 2 degrees in tilt step. The diffraction vector was maintained close to g(hkl) = 220 during the acquisition by adjusting the [110] direction of the sample parallel to the tilt axis of the holder. The observed dislocations were reconstructed by simultaneous interactive reconstruction technique, exhibiting a 3-D configuration of dislocations introduced by the three-point bending. [doi: 10.2320/matertrans.MAW200828]. |
| 145. | Masaki Tanaka, Naoki Fujimoto, Tatsuo Yokote, Kenji Higashida, Fracture toughness enhanced by severe plastic deformation in low carbon steel, NANOMATERIALS BY SEVERE PLASTIC DEFORMATION IV, PTS 1 AND 2, 584-586, 637-642, Vol.584-586, pp.637-642, 2008.08. |
| 146. | Masaki Tanaka, Naoki Fujimoto, Tatsuo Yokote, Kenji Higashida, Fracture toughness enhanced by severe plastic deformation in low carbon steel, NANOMATERIALS BY SEVERE PLASTIC DEFORMATION IV, PTS 1 AND 2, 584-586, 637-642, 2008.08, The enhancement of toughness at low temperatures in fine-grained low carbon steel was studied, basing on the theory of crack-tip shielding due to dislocations. Low carbon steel was subjected to an accumulative roll bonding (ARB) process for grain refining. The grain size perpendicular to the normal direction was decreased to approximately 200nm after the ARB process. The fracture toughness of low carbon steel with the ARB process was measured at 77K by four-point bending, comparing with the fracture toughness of those without the ARB. It was found that the value of fracture toughness at 77K was increased by grain refining due to the ARB process, indicating that the ARB process enhances toughness at low temperatures and that the brittle-to-ductile transition (BDT) temperature shifted to a lower temperature. Quasi-two-dimensional simulations of dislocation dynamics, taking into account crack tip shielding due to dislocations, were performed to investigate the effect of a dislocation source spacing along a crack front on the BDT. The simulation indicates that the BDT temperature is decreased by decreasing the dislocation source spacing.. |
| 147. | K. Higashida, M. Tanaka, A. Hartmaier, Y. Hoshino, Analyzing crack-tip dislocations and their shielding effect on fracture toughness, Mater. Sci. Eng., A, Vol.483-484, pp.13-18, 2008.06, [URL]. |
| 148. | K. Higashida, M. Tanaka, A. Hartmaier, Y. Hoshino, Analyzing crack-tip dislocations and their shielding effect on fracture toughness, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 10.1016/j.msea.2006.12.174, 483-84, 1-2 C, 13-18, 2008.06, With the aim of experimental clarification of the interaction between a crack and dislocations, crack-tip dislocations in two kinds of plastic zones in silicon crystals were directly observed by high-voltage electron microscopy to analyse by their detail characterisation. Three-dimensional analysis on crack-dislocation interaction revealed that they were shielding type dislocations in both 45 degrees-shear-type and hinge-type plastic zones, which accommodate mainly mode I stress intensity at the crack tip. The crack-tip shielding fields due to dislocations also have been visualised by photoelasticity. In specimens without pre-deformation, photoelastic images due to the mode I crack-tip field were observed when an external load was applied at room temperature. In specimens pre-deformed at high temperatures, photoelastic images corresponding to the dislocation shielding were observed. The shielding field has an effect of accommodating the tensile stress concentration due to the applied load, which increases the critical stress intensity factor for crack extension. (C) 2007 Published by Elsevier B.V.. |
| 149. | Masaki Tanaka, Naoki Fujimoto, Kenji Higashida, Fracture toughness enhanced by grain boundary shielding in submicron-grained low carbon steel, MATERIALS TRANSACTIONS, 10.2320/matertrans.ME200711, 49, 1, 58-63, Vol.49, No.1, pp.58-63, 2008.01, [URL]. |
| 150. | Microscopic Approach for Fracture Toughness of Materials. |
| 151. | Masaki Tanaka, Naoki Fujimoto, Kenji Higashida, Fracture toughness enhanced by grain boundary shielding in submicron-grained low carbon steel, MATERIALS TRANSACTIONS, 10.2320/matertrans.ME200711, 49, 1, 58-63, 2008.01, The enhancement of toughness at low temperatures in fine grained low carbon steel was studied, basing on a shielding theory due to dislocations and grain boundaries. Fully annealed low carbon steel was subjected to an accumulative roll bonding (ARB) process for grain refining. The grain size perpendicular to the normal direction was found to be approximately 200nm after the ARB process. The fracture toughness of low carbon steel ARB applied was measured at 77 K by four-point bending, comparing with the fracture toughness of those without the ARB process. It was found that the value of fracture toughness at 77 K was increased by grain refining due to the ARB, indicating that the ARB process enhances toughness at low temperatures as reported in interstitial free steel and phosphorus doped interstitial free steel. It also deduces that the brittle-ductile transition (BDT) temperature shifted to a lower temperature. The enhancement of toughness and the decrease of the BDT temperature due to grain refining cannot be explained completely by the dislocation pile-up model of dislocations at grain boundaries. Quasi-two-dimensional simulations of dislocation dynamics, taking into account of crack tip shielding due to dislocations, were performed to investigate the effect of a dislocation source spacing along a crack front on the BDT. The simulation indicated that the BDT temperature is decreased by decreasing the dislocation source spacing. In addition to the simulation, the authors suggest a new concept of accommodating stress intensity at the crack tip due to grain boundaries to explain the enhancement of toughness and the decrease of the BDT temperature in fine grained materials.. |
| 152. | Microscopic Approach for Fracture Toughness of Materials. |
| 153. | Masaki Tanaka, Yurni Hoshino, Alexander Hartmaier, Kenji Higashida, Crack tip dislocations and its shielding effect, PRICM 6: SIXTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, PTS 1-3, 561-565, PART 3, 1833-+, Vol.561-565, pp.1833-1836, 2007.12. |
| 154. | Masaki Tanaka, Yurni Hoshino, Alexander Hartmaier, Kenji Higashida, Crack tip dislocations and its shielding effect, PRICM 6: SIXTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, PTS 1-3, 561-565, PART 3, 1833-+, 2007.12, Two dimensional simulations of discrete dislocation dynamics were carried out to clarify a shielding effect due to dislocations at a crack tip. The configuration of dislocations around the crack tip was calculated under the conditions of mode I tensile load at high temperatures. The stress field around the crack tip due to dislocations was found to be compressive, accommodating mode I stress intensity at the crack tip. In order to experimentally confirm the stress accommodation, infrared photoelastic observation was also performed in a specimen pre-deformed at high temperatures. The experimental result is in good agreement with a simulated infrared photoelastic image derived from the stress field calculated.. |
| 155. | T. D. Joseph, M. Tanaka, A. J. Wilkinson, S. G. Roberts, Brittle-ductile transitions in vanadium and iron-chromium, JOURNAL OF NUCLEAR MATERIALS, 10.1016/j.jnucmat.2007.03.077, 367, SPEC. ISS., 637-643, Vol.367-370, pp.637-643, 2007.08, [URL]. |
| 156. | T. D. Joseph, M. Tanaka, A. J. Wilkinson, S. G. Roberts, Brittle-ductile transitions in vanadium and iron-chromium, JOURNAL OF NUCLEAR MATERIALS, 10.1016/j.jnucmat.2007.03.077, 367, SPEC. ISS., 637-643, 2007.08, We report ongoing experimental work on fracture and brittle-ductile transitions in vanadium, iron and iron-9% chromium single crystals and polycrystals. Tests were carried out by four-point bending of pre-cracked specimens in the temperature range 77-300 K, at a variety of strain rates. For a given material, variation of the brittle-ductile transition temperature with strain rate allows us to estimate an activation energy for the controlling process; for vanadium this was found to be similar to-0.37 eV, for iron similar to 0.21 eV and for iron-9% chromium similar to 0.11 eV. (c) 2007 Published by Elsevier B.V.. |
| 157. | A. Giannattasio, M. Tanaka, T. D. Joseph, S. G. Roberts, An empirical correlation between temperature and activation energy for brittle-to-ductile transitions in single-phase materials, PHYSICA SCRIPTA, 10.1088/0031-8949/2007/T128/017, T128, 87-90, Vol.T128, pp.87-90, 2007.03. |
| 158. | A. Giannattasio, M. Tanaka, T. D. Joseph, S. G. Roberts, An empirical correlation between temperature and activation energy for brittle-to-ductile transitions in single-phase materials, PHYSICA SCRIPTA, 10.1088/0031-8949/2007/T128/017, T128, 87-90, 2007.03, The strain rate dependence of the brittle-to-ductile transition (BDT) temperature gives the activation energy controlling the BDT. Until recently, data were only available for a limited number of materials. Experimental data on the BDT of tungsten and other bcc metals have recently become available. We have compared all the data from different materials and sources, finding a distinctive relationship between the BDT temperature (T-BDT) and the activation energy for BDT (E-BDT) which holds over a wide range of materials, temperatures and activation energy values. The ratio E-BDT/kT(BDT) gives approximately the value 25 for all the materials considered.. |
| 159. | K. Higashida, M. Tanaka, Crack Tip dislocations Observed by High-Voltage Electron-Microscopy in Single Crystal Silicon, H. Ichinose, T. Sasaki (Eds.), Proceedings of 16th International Microscopy Congress, Publication committee of IMC16, pp. 1110, 2006.08. |
| 160. | K. Higashida, M. Tanaka, Crack Tip dislocations Observed by High-Voltage Electron-Microscopy in Single Crystal Silicon, H. Ichinose, T. Sasaki (Eds.), Proceedings of 16th International Microscopy Congress, Publication committee of IMC16, 2006.08. |
| 161. | M. Tanaka, K. Higashida, H. Nakashima, H. Takagi, M. Fujiwara, Orientation dependence of fracture toughness measured by indentation methods and its relation to surface energy in single crystal silicon, INTERNATIONAL JOURNAL OF FRACTURE, 10.1007/s10704-006-0021-7, 139, 3-4, 383-394, Vol.139, No.3-4, pp.383-394, 2006.06, [URL]. |
| 162. | M. Tanaka, K. Higashida, H. Nakashima, H. Takagi, M. Fujiwara, Orientation dependence of fracture toughness measured by indentation methods and its relation to surface energy in single crystal silicon, INTERNATIONAL JOURNAL OF FRACTURE, 10.1007/s10704-006-0021-7, 139, 3-4, 383-394, 2006.06, Fracture toughness of silicon crystals has been investigated using indentation methods, and their surface energies have been calculated by molecular dynamics (MD). In order to determine the most preferential fracture plane at room temperature among the crystallographic planes containing the , and directions, a conical indenter was forced into (001), (110) and (111) silicon wafers at room temperature. Dominant {110}, {111} and {110} cracks were introduced from the indents on (001), (011) and (111) wafers, respectively Fracture occurs most easily along {110}, {111} and {110} planes among the crystallographic planes containing the , and directions, respectively. A series of surface energies of those planes were calculated by MD to confirm the orientation dependence of fracture toughness. The surface energy of the {110} plane is the minimum of 1.50 J m(-2) among planes containing the and directions, respectively, and that of the {111} plane is the minimum of 1.19 J m(-2) among the planes containing the direction. Fracture toughness of those planes was also derived from the calculated surface energies. It was shown that the K-IC value of the {110} crack plane was the minimum among those for the planes containing the and directions, respectively, and that K-IC value of the {111} crack plane was the minimum among those for the planes containing the direction. These results are in good agreement with that obtained conical indentation.. |
| 163. | K Higashida, M Tanaka, R Onodera, HVEM study of crack tip dislocations in silicon crystals, PRICM 5: THE FIFTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, PTS 1-5, 475-479, V, 4043-4046, Vol.475-479, pp.40-43, 2005.11. |
| 164. | K Higashida, M Tanaka, R Onodera, HVEM study of crack tip dislocations in silicon crystals, PRICM 5: THE FIFTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, PTS 1-5, 475-479, V, 4043-4046, 2005.11, The present paper describes the nature of crack tip plasticity in silicon crystals examined by high voltage electron microscopy (HVEM) and atomic force microscopy (AFM). Firstly, AFM images around a crack tip are presented, where the formation of fine slip bands with the step heights of one or two nanometers is demonstrated. Secondly, crack-tip dislocations observed by HVEM are exhibited, where it is emphasized that dislocation characterization is essential to consider the relief mechanism of crack-tip stress concentration.. |
| 165. | M Tanaka, K Higashida, High-voltage electron-microscopical observation of crack-tip dislocations in silicon crystals, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 10.1016/j.msea.2005.02.084, 400, 1-2 SUPPL., 426-430, Vol.400-401, pp.426-430, 2005.07, [URL]. |
| 166. | M Tanaka, K Higashida, High-voltage electron-microscopical observation of crack-tip dislocations in silicon crystals, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 10.1016/j.msea.2005.02.084, 400, 1-2 SUPPL., 426-430, 2005.07, Crack-tip dislocations in silicon single crystals were observed by high-voltage electron microscopy. Cracks were introduced into silicon wafers at room temperature by a Vickers indenter. The indented specimens were annealed at 823 K in order to activate dislocation emission from the crack tip under the residual stress due to the indentation. In the specimen without annealing, no dislocations were observed around the crack. On the other hand, in the specimen after the annealing, the aspect of the early stage of dislocation emission was observed, where dislocations were emitted not as a perfect dislocation but as a partial dislocation in the hinge-type plastic zone. Prominent dislocation arrays that were emitted from a crack tip were also observed, and they were found to be of shielding type, which increases the fracture toughness of those crystals. (c) 2005 Elsevier B.V. All rights reserved.. |
| 167. | K Higashida, M Tanaka, E Matsunaga, H Hayashi, Crack tip stress fields revealed by infrared photoelasticity in silicon crystals, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 10.1016/j.msea.2004.05.058, 387, 1-2 SPEC. ISS., 377-380, Vol.387-389, pp.377-380, 2004.12, [URL]. |
| 168. | M Tanaka, K Higashida, T Haraguchi, Microstructure of plastic zones around crack tips in silicon revealed by HVEM and AFM, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 10.1016/j.msea.2004.05.040, 387, 1-2 SPEC. ISS., 433-437, Vol.387-389, pp.433-437, 2004.12, [URL]. |
| 169. | K Higashida, M Tanaka, E Matsunaga, H Hayashi, Crack tip stress fields revealed by infrared photoelasticity in silicon crystals, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 10.1016/j.msea.2004.05.058, 387, 1-2 SPEC. ISS., 377-380, 2004.12, Stress fields around a crack tip in silicon crystals have been investigated by using infrared photoelasticity with the aim of clarifying the shielding effect due to crack tip dislocations on the steep increase of fracture toughness in the brittle-to-ductile transition (BDT). First, compact tension tests were carried out at room temperature to make in situ observation of elastic behavior of crack tip stress fields. The photoelastic images observed were in good agreement with those simulated for the usual elastic fields around the tip of a mode I crack. Next, to clarify the stress modification due to crack tip plasticity, three-point bending tests were also made by using notched specimens at high temperatures around 1000 K. After the high temperature test, in spite of the absence of the applied load, residual bright images were observed around the notch. Those images correspond to an internal stress due to dislocations multiplied around the notch, and they have an effect of shielding (accommodating) the stress concentration due to the applied load. The fracture toughness at room temperature was increased by the introduction of the residual stress. (C) 2004 Elsevier B.V. All rights reserved.. |
| 170. | M Tanaka, K Higashida, T Haraguchi, Microstructure of plastic zones around crack tips in silicon revealed by HVEM and AFM, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 10.1016/j.msea.2004.05.040, 387, 1-2 SPEC. ISS., 433-437, 2004.12, In order to understand the dislocation process for the sharp brittle-to-ductile transition in silicon crystals, microstructures of plastic zones around crack tips have been investigated using high-voltage electron microscopy (HVEM) and atomic force microscopy (AFNI). Cracks were introduced into {110} silicon wafers at room temperature by Vickers indentation method. The temperature of specimens indented was raised to higher than 823K to activate dislocation sources around a crack tip under the presence of residual stress due to the indentation. The crack observed was extending along the direction from the edge of the indent. AFNI study has revealed two types of fine slip bands around the crack tip: one type of slip bands is those parallel to , and another type is those parallel to the direction. The former is corresponding to so-called hinge-type plastic zone, and the latter is 45degrees-shear-type. HVEM study has revealed the characteristics of dislocation structures corresponding to the both types of plastic zones. Detailed analyses of each dislocation, including the determination of the sign of Burgers vector, have been made to characterize those plastic zones. (C) 2004 Elsevier B.V. All rights reserved.. |
| 171. | M Tanaka, K Higashida, T Fukui, T Yokote, HVEM study of crack-tip dislocations in Si crystals prepared by FIB and twin-blade cutting method, JOURNAL OF ELECTRON MICROSCOPY, 10.1093/jmicro/dfh052, 53, 5, 505-509, Vol.53, No.5, pp.353-360, 2004.10, [URL]. |
| 172. | M Tanaka, K Higashida, T Fukui, T Yokote, HVEM study of crack-tip dislocations in Si crystals prepared by FIB and twin-blade cutting method, JOURNAL OF ELECTRON MICROSCOPY, 10.1093/jmicro/dfh052, 53, 5, 505-509, 2004.10, Crack-tip dislocations in silicon crystals have been examined by using high-voltage electron microscopy. Cracks were introduced by the Vickers indentation method at room temperature and the indented specimens were annealed at high temperatures to induce dislocations around crack tips under the presence of residual stress due to the indentation. A selected area around a crack tip was thinned by a focused ion beam (FIB) technique. Specimens were thinned in advance by a twin-blade cutting (TBC) method, which is a simple cutting process for saving FIB machine time. A combination of FIB and TBC can be a useful thinning procedure for the efficient preparation of transmission electron microscopy specimens. Characteristic dislocation structures were observed around the tip of a crack, aiding the elucidation of dislocation processes, which is essential to increase the fracture toughness of materials.. |
| 173. | , [URL]. |
| 174. | M Tanaka, K Higashida, H Nakashima, H Takagi, M Fujiwara, Orientation dependence of fracture toughness and its relation to surface energy in Si crystals, JOURNAL OF THE JAPAN INSTITUTE OF METALS, 10.2320/jinstmet.68.787, 68, 9, 787-791, 2004.09. |
| 175. | M Tanaka, K Higashida, H Nakashima, H Takagi, M Fujiwara, Orientation dependence of fracture toughness and its relation to surface energy in Si crystals, JOURNAL OF THE JAPAN INSTITUTE OF METALS, 10.2320/jinstmet.68.787, 68, 9, 787-791, 2004.09, Fracture toughness of silicon crystals has been investigated using indentation methods and their surface energies have been calculated by molecular dynamics (MD). In order to determine the most preferable fracture plane at room temperature, a conical indenter was forced into a (001) silicon wafer at room temperature. Dominant {110} cracks were introduced from the indent, indicating that fracture occurs most easily along the {110} plane among the crystallographic planes of the zone. To confirm this orientation dependence of fracture toughness, surface energies for those planes were computed using molecular dynamics. The surface energy calculated exhibits the minimum value of 1.50 J(.)m(-2) at the {100} plane and it increases up to 2.26 J(.)m(-2) at the {100} plane. Fracture toughness was derived from these computed surface energies, and it was shown that K-IC value for the {110} crack plane was the minimum among those for the planes of the zone. Fracture toughness of {110} plane and the other planes of zone were measured by the indentation fracture (IF) method. The result is qualitatively in a good agreement with those obtained from the MD, although the absolute KIC values estimated by the IF method were larger than those obtained by the calculation.. |
| 176. | M Tanaka, K Higashida, HVEM characterization of crack tip dislocations in silicon crystals, JOURNAL OF ELECTRON MICROSCOPY, 10.1093/jmicro/dfh051, 53, 4, 353-360, Vol.53, No.5, pp.505-509, 2004.08, [URL]. |
| 177. | K. Higashida, M. Tanaka, 3D Structures of Crack-Tip Dislocations in Silicon Revealed by HVEM, C. Gundlach, K. Haldrup, N. Hansen, X. Huang, D.J. Jensen, T. Leffers, Z.J. Li, S.F. Nielsen, W. Pantleon, J.A. Wert, G. Winther (Eds.), Proceedings of the 25th Risoe International Symposium on Materials Science: Evolution of Deformation Microstructures in 3D, Risoe National Laboratory, Roskide, Denmark,, pp. 337-342, 2004.08. |
| 178. | K. Higashida, M. Tanaka, 3D Structures of Crack-Tip Dislocations in Silicon Revealed by HVEM, C. Gundlach, K. Haldrup, N. Hansen, X. Huang, D.J. Jensen, T. Leffers, Z.J. Li, S.F. Nielsen, W. Pantleon, J.A. Wert, G. Winther (Eds.), Proceedings of the 25th Risoe International Symposium on Materials Science: Evolution of Deformation Microstructures in 3D, Risoe National Laboratory, Roskide, Denmark,, 2004.08. |
| 179. | M Tanaka, K Higashida, HVEM characterization of crack tip dislocations in silicon crystals, JOURNAL OF ELECTRON MICROSCOPY, 10.1093/jmicro/dfh051, 53, 4, 353-360, 2004.08, Crack tip dislocations in silicon crystals have been studied using high voltage electron microscopy (HVEM). The dislocation images have been investigatcd by cornparing the observed images to those that were simulated. Dislocation images were computed in the conditions g (.) b = 0, 1 or 2 (g: diffraction vector, b: Burgers vector). The characteristics of 60degrees dislocations were examined in detail since these dislocations are not characterized only by the condition g (.) b = 0 criterion. The computed images were in good agreement with those observed by HVEM. Residual contrasts of 60degrees dislocations under the condition g (.) b = 0 exhibited characteristic black-and-white contrasts, which can contribute to the characterization of the dislocations. Such characterization of dislocations is essential in order to clarify the dislocation mechanism which controls the fracture toughness of materials.. |
| 180. | K Higashida, M Tanaka, HVEM/AFM studies on crack tip plasticity in Si crystals, IUTAM SYMPOSIUM ON MESOSCOPIC DYNAMICS OF FRACTURE PROCESS AND MATERIALS STRENGTH, 115, 153-162, 153-162, 2004.07. |
| 181. | K Higashida, M Tanaka, HVEM/AFM studies on crack tip plasticity in Si crystals, IUTAM SYMPOSIUM ON MESOSCOPIC DYNAMICS OF FRACTURE PROCESS AND MATERIALS STRENGTH, 115, 153-162, 2004.07, Crack tip plasticity in silicon crystals has been studied by both high voltage electron microscopy (HVEM) and atomic force microscopy (AFM). Cracks were introduced into silicon wafers at room temperature by Vickers indentation method. Specimens indented were annealed at temperatures higher than 773K to activate dislocation sources around a crack tip under the residual stress due to the indentation. In the present study, two types of plastic zones were examined: the 45degrees-shear-type in {001} wafers and hinge-type in {011} wafers. In AFM observations, very fine and sharp slip bands were found around crack tips in both types of plastic zones, where the step heights in the slip bands were around a few nanometers. In HVEM study, characteristic dislocation configurations have been observed in each type of plastic zone Contrast simulations for the dislocations revealed riot only their slip systems but also the signs of their Burgers vectors. The dislocation structures characterized by HVEM correspond well with the slip bands found by AFM. Those dislocations were shielding-type, which contributes to the increase of facture toughness to cause the sharp brittle-to-ductile transition of silicon crystals.. |
| 182. | M Tanaka, K Higashida, H Nakashima, H Takagi, M Fujiwara, Fracture toughness evaluated by indentation methods and its relation to surface energy in silicon single crystals, MATERIALS TRANSACTIONS, 10.2320/matertrans.44.681, 44, 4, 681-684, Vol.44, No.4, pp.681-684, 2003.04, [URL]. |
| 183. | M Tanaka, K Higashida, H Nakashima, H Takagi, M Fujiwara, Fracture toughness evaluated by indentation methods and its relation to surface energy in silicon single crystals, MATERIALS TRANSACTIONS, 10.2320/matertrans.44.681, 44, 4, 681-684, 2003.04, Fracture toughness of silicon crystals has been investigated by indentation methods, and their surface energy has been calculated using molecular dynamics (MD). When a conical indenter was forced into a (001) silicon wafer at room temperature, {110} cracks were mainly introduced from the indent, indicating that fracture occurs most easily along the {110} plane among the crystallographic planes of the zone. To confirm this orientation dependence, surface energies for those planes were computed using molecular dynamics. The surface energy calculated exhibits the minimum value of 1.50J.m(-2) at the {110} plane, and it increases up to 2.26 J.m(-2) at the (100) plane. Fracture toughness was derived from these computed surface energies, and it was shown that K-IC value for the {110} crack plane was the minimum among those for the planes of the zone. This result is in good agreement with that obtained by indentation fracture (IF) methods, although the absolute K-IC values evaluated by the IF method were larger than those obtained by the calculation.. |
| 184. | K Higashida, N Narita, M Tanaka, T Morikawa, Y Miura, R Onodera, Crack tip dislocations in silicon characterized by high-voltage electron microscopy, PHILOSOPHICAL MAGAZINE A-PHYSICS OF CONDENSED MATTER STRUCTURE DEFECTS AND MECHANICAL PROPERTIES, 10.1080/01418610210141307, 82, 17-18, 3263-3273, Vol.82, No.17/18, pp.3263-3273, 2002.11, [URL]. |
| 185. | Dislocation Configurations near a Crack Tip and Its Infiuence on the Fracture Toughness in Silicon Crystals Dislocations emitted from a crack tip in silicon single crystals have been investigated using a high voltage electron microscopy (HVEM). The influence of those crack tip dislocations on the fracture toughness has been discussed based on the 3-D stress analysis of crack-dislocation interaction. Pure screw dislocations were introduced not only ahead of a crack tip but also behind the tip. The dislocations ahead of the crack tip have the sign of Burgers vectors opposite to that of the dislocations behind the tip. These configurations of crack tip dislocations are understood by dislocation loop expansion from sources near the crack tip. The contribution to the fracture toughness by those crack tip dislocations was calculated, and it was found that 70∼90% increase in the fracture toughness was caused by a dislocation configuration corresponding to that observed in the early stage of dislocation emission from a crack tip.. |
| 186. | K Higashida, N Narita, M Tanaka, T Morikawa, Y Miura, R Onodera, Crack tip dislocations in silicon characterized by high-voltage electron microscopy, PHILOSOPHICAL MAGAZINE A-PHYSICS OF CONDENSED MATTER STRUCTURE DEFECTS AND MECHANICAL PROPERTIES, 10.1080/01418610210141307, 82, 17-18, 3263-3273, 2002.11, The nature of crack tip dislocations and their multiplication processes in silicon crystals have been examined by using high-voltage electron microscopy. Cracks were introduced by the Vickers indentation method at room temperature, and the specimen indented was annealed at high temperatures to induce dislocation generation around the crack tip under the presence of residual stress due to the indentation. In the specimens annealed, fine slip bands with the step heights of around 1 nm were formed along the{111} slip planes near the crack tip. The crack tip dislocations observed were characterized by matching their images to those simulated, and it was found that two different slip systems were activated even in the early stage of dislocation emission. With the increase in the number of crack tip dislocations, more complicated dislocation configurations such as dislocation tangles were formed around the crack tip, showing the beginning of multiplication of crack tip dislocations which causes effective crack tip shielding.. |
| 187. | Dislocation Configurations near a Crack Tip and Its Infiuence on the Fracture Toughness in Silicon Crystals Dislocations emitted from a crack tip in silicon single crystals have been investigated using a high voltage electron microscopy (HVEM). The influence of those crack tip dislocations on the fracture toughness has been discussed based on the 3-D stress analysis of crack-dislocation interaction. Pure screw dislocations were introduced not only ahead of a crack tip but also behind the tip. The dislocations ahead of the crack tip have the sign of Burgers vectors opposite to that of the dislocations behind the tip. These configurations of crack tip dislocations are understood by dislocation loop expansion from sources near the crack tip. The contribution to the fracture toughness by those crack tip dislocations was calculated, and it was found that 70∼90% increase in the fracture toughness was caused by a dislocation configuration corresponding to that observed in the early stage of dislocation emission from a crack tip.. |
| 188. | M Tanaka, K Higashida, T Kishikawa, T Morikawa, HVEM/AFM observation of hinge-type plastic zones associated with cracks in silicon crystals, MATERIALS TRANSACTIONS, 10.2320/matertrans.43.2169, 43, 9, 2169-2172, Vol.43, No.9, pp.2169-2172, 2002.09, [URL]. |
| 189. | M Tanaka, K Higashida, T Kishikawa, T Morikawa, HVEM/AFM observation of hinge-type plastic zones associated with cracks in silicon crystals, MATERIALS TRANSACTIONS, 10.2320/matertrans.43.2169, 43, 9, 2169-2172, 2002.09, Dislocation structures developed in hinge-type plastic zones associated with cracks in silicon crystals have been studied using a high voltage electron microscope (HVEM). Fine slip bands due to those dislocations have been also examined by an atomic force microscope (AFM). {100} and {110} cracks were introduced into {110} silicon wafers at room temperature by Vickers indentation method. The temperature of the wafer chips indented was raised to higher than 823 K to activate dislocations around crack tips under a residual stress due to the indentation. In specimens with the heat-treatment, prominent dislocation arrays corresponding to the hinge-type plastic zone were observed not only near the crack tip but also in the crack wake. AFM observations showed that very fine slip bands with the step height of a few nano-meters were formed with the regular spacing of a few microns. Based on the analyses of those dislocations and slip bands, it has been revealed that those dislocations were shielding-type increasing the fracture toughness.. |
| 190. | M Tanaka, T Fukui, T Yamagata, T Morikawa, K Higashida, R Onodera, TEM/AFM observation of crack tip plasticity in silicon single crystals, MATERIALS TRANSACTIONS, 10.2320/matertrans.42.1839, 42, 9, 1839-1842, Vo.42, No.9, pp.1839-1842, 2001.09, [URL]. |
| 191. | M Tanaka, T Fukui, T Yamagata, T Morikawa, K Higashida, R Onodera, TEM/AFM observation of crack tip plasticity in silicon single crystals, MATERIALS TRANSACTIONS, 10.2320/matertrans.42.1839, 42, 9, 1839-1842, 2001.09, Crack tip plasticity in silicon single crystals has been investigated using both high voltage electron microscopy (HVEM) and atomic force microscopy (AFM). Cracks were introduced into a (001) silicon wafer at room temperature by Vickers indentation method. The specimen temperature was increased to more than 873 K to activate dislocation generation around the crack tip under a residual stress due to the indentation. In specimens without the heat-treatment, no dislocations were observed around the crack, while in specimens with the heat-treatment, characteristic dislocation configurations were observed near the crack tip. AFM observations showed that slip bands were formed around the crack tip in the heat-treated specimens, and that the step heights of those slip bands were around one nanometer. Such crack tip plasticity is considered to be caused by mainly mode I tensile load, and contribute to increasing fracture toughness.. |
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