無電解ニッケルメッキ材の疲労強度

Abstract

The rotating bending fatigue tests were performed on the electroless nickel plated steels at room temperature, and the effects of thickness of plating and baking temperature after plating on the fatigue strength were investigated. Furthermore, the characteristics of deposited film itself were discussed.The electroless nickel plating of the specimens used was carried out at 90°C, pH 6, in a plating bath of the following compositions; NiSO4·6H2O: 30g/l; NaH2PO2·H2O: 10g/l; NaC2H3O2·3H2O: 10g/l.The results obtained are as follows:(1) When the electroless nickel plating is carried out on carbon steels, their fatigue strength rather increases, contrary to the case of electro-deposit steels. This improvement is independent of the thickness of deposited film and carbon content of steels. The rate of increase in fatigue strength against non-plated specimens is about 16∼17% for both steels.(2) The electrolessly deposited nickel film shows very satisfactory adhesion to the substratum under fatigue fracture condition. The fatigue damage of plated steels is suppressed by deposited film. Consequently, the nucleation of fatigue crack is delayed, resulting in the increase in fatigue strength.(3) By baking treatment, the micro-hardness of deposited film increases, accompanied with structural changes. This increase is due to the precipitation hardening of Ni3P. At the same time, the tensile residual stress in deposited film is reduced. The rotating bending fatigue strength, however, is not affected. Therefore, it is not expected that the fatigue strength is improved by means of the baking treatment after the electroless plating.