Influence of Internal Stress on Plating Crack in Ni-W Alloy Electroplating

Abstract

a 新日鐵住金㈱ 鉄鋼研究所 (〒 660-0891 兵庫県尼崎市扶桑町 1-8) b 新日鐵住金㈱ 先端技術研究所 (〒 660-0891 兵庫県尼崎市扶桑町 1-8) c 岡山大学 大学院自然科学研究科 (〒 700-8530 岡山県岡山市北区津島中 3-1-1)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.

Features of Ni-W Plating Film Obtained by the Jet-Flow System

“…A straight line of 130 µm was arbitrarily drawn in the field of view observed with a nanosearch microscope (OLS4500, Olympus, Tokyo, Japan) 2000×, cracks intersecting the line were counted, and converted to the number of intersections per 1 mm. The number of fields of view was 2, and cracks were counted with three lines in each field of view, and the average value was adopted [15]. Figure 2 shows an example of counting cracks.…”

“…the line were counted, and converted to the number of intersections per 1 mm. T ber of fields of view was 2, and cracks were counted with three lines in each field and the average value was adopted [15]. Figure 2 shows an example of counting…”

“…It has already been reported that Ni-W plating has high wear resistance and hardness [12,13]. However, Ni-W plating film has many problems, such as cracks easily, low current efficiency, and high internal stress [14,15], and has not been widely put into practical use. Even if the corrosion resistance of the Ni-W plating film is high, it is necessary to be careful because corrosion factors, such as gas and plating solution that enter from cracks, corrode the base of the plating film and deteriorate the performance of the film.…”