Papers by Author: Atsushi Yamamoto

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Authors: Atsushi Yamamoto, Atsushi Watanabe, Harushige Tsubakino, Shinji Fukumoto
Authors: Atsushi Yamamoto, Akikazu Sato, Koji Kato, An Pong Tsai, Tsuyoshi Masumoto
Authors: Harushige Tsubakino, Atsushi Yamamoto, K. Sugahara, Shinji Fukumoto
Authors: Youhei Sakamaki, Kosuke Kuwabara, Gu Jiajun, Haruyuki Inui, Masaharu Yamaguchi, Atsushi Yamamoto, Haruhiko Obara
Authors: Harushige Tsubakino, Atsushi Nogami, Atsushi Yamamoto, Mititaka Terasawa, Tohru Mitamura, Tomoaki Yamanoi, Atsushi Kinomura, Yuji Horino
Authors: Atsushi Yamamoto, Harushige Tsubakino, Masami Ando, Lie Liu, Mititaka Terasawa, Tohru Mitamura
Abstract: Ion-implantation on high purity iron substrates with nitrogen ions were carried out by using a Cockcroft Walton type accelerator under an accelerating voltage of 150 kV. Hardness measurements on the implanted surfaces showed that hardness effectively increased in the cold rolled specimens by ion-implantation in comparison with in an annealed specimen. Iron nitride, Fe16N2, was formed in the ion-implanted specimens. In the annealed specimen, relatively large particles of Fe16N2 were formed with low number density, while in the deformed specimens, dislocation substructures due to cold rolling were disappeared by ion-implantation and fine particles were densely formed. Strain field around dislocations induced by deformation provides nucleation sites for Fe16N2 particles.
Authors: Atsushi Yamamoto, Harushige Tsubakino, Akira Suehiro, Atsushi Watanabe
Authors: Katsuhiko Inoue, Bin Zhang, Atsushi Yamamoto, Harushige Tsubakino
Abstract: The life limit of the standard hardness block of HRC64 made from JIS-SUJ2 steel was evaluated. The HRC64 specimens were annealed at temperatures ranging from 55 to 200C for about 104 h in maximum. The micro-Vickeres hardness decreased with the annealing time at all temperatures after some incubation periods. Transmission electron microscopy (TEM) showed that the microstructure of the specimen before annealing was composed of primary cementite particles, carbide and martensite matrix. After annealing, fine cementite particles of about few tens of nanometers in size were observed. The decrease in hardness during annealing was caused by the precipitation of the cementite. The life limit keeping the standard hardness value at ambient temperature was estimated to be about 3.5-4 years based on extrapolation of the annealing curves at various temperatures.
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