||Hiroyuki Toda, Akihisa Takijiri, Masafumi Azuma, Shohei Yabu, Kunio Hayashi, SEO DOWON, Masakazu Kobayashi, Kyosuke Hirayama, Akihisa Takeuchi, Kentaro Uesugi, Damage micromechanisms in dual-phase steel investigated with combined phase- and absorption-contrast tomography, Acta Materialia , 126, 401-412, 2017.03.
||Hiroyuki Toda, Takanobu Kamiko, Yasuto Tanabe, Masakazu Kobayashi, D. J. Leclere, Kentaro Uesugi, Akihisa Takeuchi, Kyosuke Hirayama, Diffraction-amalgamated grain boundary tracking for mapping 3D crystallographic orientation and strain fields during plastic deformation, Acta Materialia, 107, 310-324, 2016.04.
||Kyosuke HIrayama, Yasuhiro Morizono, Sadahiro Tsurekawa, Yasuyoshi Hidaka, Yonosuke Yoshii, Grain Boundary Engineering of 10% Cr Ferritic-Martensitic Steel SUH3, ISIJ International, 2015.05, Thermomechanical treatments for manipulating grain boundary microstructure in 10 wt%Cr ferriticmartensitic steel SUH3 have been studied. Material with a high fraction of coincidence site lattice (CSL) boundaries was successfully produced and subjected to steam oxidation tests to demonstrate the utility of grain boundary engineering. Introducing a high fraction of twin boundaries in austenite resulted in a significant increase in the number of CSL boundaries along the prior austenite grain boundaries in martensite. In addition, grain boundary engineering introduced a high density of subblock structures in martensite, which resulted in a homogeneous distribution of fine precipitates in tempered martensite. Steam oxidation tests demonstrated that grain boundary engineering for SUH3 steel can achieve enhanced oxidation resistance..
||Seiichiro Ii, Kyosuke Hirayama, Kyohei Matsunaga, Hiromichi Fujii, Sadahiro Tsurekawa, Direct measurement of local magnetic moments at grain boundaries in iron, Scripta Materialia, 2012.11, We have succeeded for the first time to directly measure the local magnetic moments in the vicinity of well-characterized grain boundaries in pure iron by electron energy loss spectroscopy on transmission electron microscope. The measured local magnetic moments are larger at the grain boundary than in the grain interior. This enhancement of magnetic moments depends on the grain boundary character. These findings suggest that the local magnetic moments at grain boundaries are likely to correlate with the free volume at grain boundaries..
||Kyosuke Hirayama, Seiichiro Ii, Sadahiro Tsurekawa, Transmission electron microscopy/electron energy loss spectroscopy measurements and ab initio calculation of local magnetic moments at nickel grain boundaries, Science and Technology of Advanced Materials, 2014.01, We have determined local magnetic moments at nickel grain boundaries using a transmission electron microscopy/electron energy loss spectroscopy method assuming that the magnetic moment of Ni atoms is a linear function of the L3/L2 (white-line ratio) in the energy loss spectrum. The average magnetic moment measured in the grain interior was 0.55μB, which agrees well with the calculated magnetic moment of pure nickel (0.62μB). The local magnetic moments at the grain boundaries increased up to approximately 1.0μB as the mis-orientation angle increased, and showed a maximum around 50. The respective enhancement of local magnetic moments at the 65 (0.63μB) and random (0.90μB) grain boundaries in pure nickel was approximately 14 and 64% of the grain interior. In contrast, the average local magnetic moment at the (111) 63 grain boundary was found to be 0.55μB and almost the same as that of the grain interior. These results are in good agreement with available ab initio calculations..