Papers by Author: Kenji Murakami

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Authors: T. Buchholz, J. Alkemper, Kenji Murakami, Lorenz Ratke
Authors: T. Ishiyama, E. Katayama, Kenichiro Takahei, Akihito Taguchi, Kenji Murakami
Authors: Kenji Murakami
Abstract: Pure nickel powder was low pressure plasma sprayed onto a steel substrate held at different temperatures during spraying. The as-sprayed coatings consist of columnar grains whose axes are nearly perpendicular to the lamellae composing the coatings. As the coating temperature becomes higher, the length of the columnar grains increases and is longer than the thickness of the lamellae, indicating the growth of the grains across the lamellar interfaces during spraying. On the other hand, the coatings that were heat treated after spraying consist of coarse equiaxed grains. The coatings that experienced high temperatures during spraying or the heat treated coatings have large porosity and contain large globular pores. The hardness, apparent density and the tensile strength of the coating itself were the highest for the coating prepared at a low temperature and became low on heat treatment. The thermal conductivity in the direction perpendicular to the coating was the largest for the coating that consisted of long columnar grains.
Authors: M. Kitajima, K. Ishioka, K.G. Nakamura, N. Fukata, Kenji Murakami, Jun Kikuchi, S. Fujimura
Authors: Tetsuya Senda, Yoh-Ichi Kawagoe, Noriyuki Kotani, Kenji Murakami, Koshi Adachi
Abstract: Sliding wear surfaces of alumina were observed by transmission and scanning electron microscopy. Wear loss was very low (<10-7 mm3/Nm) at room temperature whereas it was high (>10-5 mm3/Nm) at 500oC. In a mild wear regime at room temperature, a layer of very fine particles (10 nm or less) is observed on the wear surface. Beneath the layer, a deformed bulk surface with extensive dislocations is observed. The layer exhibits a diffraction pattern of a meta-stable phase which is dissimilar to the original α-alumina. The layer appears to act as lubrication film at the contact interface to reduce the wear loss. In a severe wear regime at 500oC, a similar structure consisting of a fine-particle layer and deformed bulk surface is observed. However, extensive microcracks are observed in the layer and the bulk underneath that cause further material removal resulting in a high wear rate.
Authors: Kenji Murakami, Nobuhiro Fujita, S. Adachi, Hideo Nakajima, H. Miyake
Abstract: Copper, iron and a nickel-chromium alloy were thermal sprayed onto a mild steel substrate in air and the structures of the sprayed particles that were collected during flying and those of the coatings are examined. The coatings consist of metal layers and metal oxide layers, and the minor phase layers become disintegrated and granulated on annealing. This morphology change is caused by the balance of the boundary energies.
Authors: Yasuhiro Hoshiyama, Kentaro Hirano, Hidekazu Miyake, Kenji Murakami
Abstract: Fe-B-Cr alloy powder in diameter of 32-53 μm made by argon atomization is low-pressure plasma sprayed to produce a rapidly solidified iron base composite deposit with finely dispersed boride particles. The constituents of the as-sprayed deposit formed on a water-cooled substrate are α phase and amorphous phase that are supersaturated with chromium and boron due to high cooling rate during solidification of the melt. Heat treatment of deposit at 873K leads to decomposition of the amorphous phase, resulting in the formation of Fe3B. The deposit heat treated above 1073K is composed of α phase and (Fe,Cr)2B. The as-sprayed deposit produced on a non-cooled substrate consists of α phase and (Fe,Cr)2B. The fine precipitates of about 0.1 μm in the as-sprayed deposit coated on a non-cooled substrate are boride. As deposit temperature increases, the coarsening of the precipitate particles results in lowered hardness of deposits.
Authors: N. Fukata, S. Fujimura, Kenji Murakami
Authors: Kenji Murakami, Takasumi Ohyanagi, Kazusato Hara, K. Masuda
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