Papers by Author: Masahiko Kato

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Authors: Keijiro Nakasa, Taufiq Arif Setyanto, Bo Zhang, Jin Hua Zheng, Masahiko Kato
Abstract: Pure titanium substrate specimen was sputter-coated with SiC or CoCrNi-oxide thin film and the wear test was carried out by using a “ball-on-disk” type testing machine. The semi-circular parallel cracks appeared on the film surface with angles of 45 degree to the sliding direction of the SiC ball and the delamination of film quickly occurred after the cracking. With the aid of finite element methods, stress distribution before and after cracking in the film was obtained. The maximum tensile stress existing in the film at the back-contact edge of ball is the reason for the initiation of semi-circular parallel cracks. After the film is cracked, the tensile stress normal to interface as well as the shear stress along interface appear at crack tip. The combination of these two stresses is the main reason for the delamination after the film is cracked.
Authors: Cheng Wei Li, Masahiko Kato, Keijiro Nakasa
Abstract: Decarburization treatment was carried out on SKD5 tool steel by heating at 1323K for maximum 5.4ks and quenching followed by tempering at 873K for 3.6ks. This resulted in decarburized layer of maximum thickness 0.45mm. After the treatment, WC-Co cermet of 0.2mm thickness was deposited by high-velocity oxygen fuel thermal spraying. Tensile tests were carried out on the specimens, where the load was applied parallel to the specimen. The results show that the presence of decarburized layer increases the interfacial fracture toughness. The reason seems to be that the large plastic deformation of decarburized layer relieves shear and tensile stresses at crack tip. Edge indent tests were also conducted, where shear delamination of coating occurred during the penetration of indenter. The result is that the delamination energy decreases due to the presence of decarburized layer, which is contrary to that of the tensile test. The shear fracture of soft decarburized layer may be the reason for the smaller delamination energy of decarburized specimen.
Authors: Lin Gao, Keijiro Nakasa, Masahiko Kato, Hidetaka Nishida
Authors: Keijiro Nakasa, Masahiko Kato, Bo Zhang, Noriyuki Akitake
Abstract: Thermal barrier coating (TBC) was carried out on Ni based super-alloy specimens, and edge indent tests were carried out at 1073K under different displacement rate. In addition, the specimens were heated and held at 1273K for long time, and the edge-indent tests of the specimens were performed both at 1273K and at room temperature. The results showed that the delamination load Pd and the delamination energy Ed measured at 1073K after short time holding were larger than those measured at room temperature, and the Pd and Ed slightly decreased with increasing displacement rate at 1073K while they slightly increased at 293K. The Pd and Ed at 1273K increased with increasing holding time and reached a maximum at 1400ks. With further increase in holding time, the Pd and Ed largely decreased. The Pd and Ed measured at 1273K were smaller than those at room temperature.
Authors: Keijiro Nakasa, Masahiko Kato, Jin Hua Zheng
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