電着Niナノ結晶バルク材の疲労特性に及ぼす結晶粒径の影響

抄録

Nickel plates with thickness of 1 mm were produced by electrodeposition using sulfamate solution under four conditions with and without brightener. The distribution of the grain size in the thickness direction was almost uniform for two conditions : CC00-55 without brightener and CC20-40 with the highest brightener content 2.0 g/L, while the other two cases showed large distribution: CC05-55 and CC10-55. The tensile yield stress of two uniform bulks was increased with decreasing grain size following the Hall-Petch relation obtained for thin films with 10 μm in thickness produced by electrodeposition. Non-uniform bulks show the yield stress corresponding to the mean value of the grain size. In the relation between fatigue crack propagation rate and stress intensity factor, bulks tended to show slower growth rate compared with thin films produced by the same electrodeposition condition. The threshold stress intensity factor ΔK_th increased roughly proportionally to the square root of the grain size. The ΔK_th value of non-uniform bulks was controlled by the larger grain size within thickness. The fatigue crack propagation rate was very much influenced by the crack path, grain size as well as the applied stress intensity factors.