Ni-W合金めっきの皮膜クラックに及ぼすめっき内部応力の影響

Abstract

Ni-W alloy plating has been considered for application to various industrial fields as a substitute for hard Cr plating. However, by plating conditions, the plating crack on Ni-W alloy film might occur and cause difficulties in industrial use. In this study, we elucidated the plating crack behavior of Ni-W alloy films with various W contents. We also investigated the influence of the internal stress of Ni-W alloy film on the plating cracks. Results show that the number of the plating cracks changed by W content in the range of 27.3-51 wt%W. At approximately 40 wt%W, plating cracks did not occur. Moreover, the change of the internal stress of Ni-W alloy film in the range of 30-46 wt%W showed a convex-downward curve against the W content, which indicated the least internal stress in approximately 40 wt%W. Furthermore, the influence of the misfit between the Ni-W alloy film and that substrate was small, which suggests that the internal stress of the film itself changed. Therefore, the internal stress was regarded as a direct factor affecting the plating crack. Furthermore, from results of X-ray diffraction patterns of Ni-W alloy films with various W contents, the change of the internal stress was inferred to have resulted from the change of the crystalline state.