Abstract
The object of this study was to determine the effects of heat treatment on the hardness of W-Ni alloy plating films electrodeposited from citric acid-ammoniacal plating solution, which was proposed by Vaaler and Holt, containing 20g/l of NiSO4⋅6H2O, 50g/l of Na2WO4⋅2H2O, 66g/l of citric acid, and NH4OH for giving a definite pH. The solution was used at 60°C, pH of 8.6-8.9 and current density of 10A/dm2 based on a series of preliminary tests.
The following results were obtained.
(1) The hardness of W-Ni alloy plating film, heated in vacuum up to a certain temperature below 600°C, was remarkably increased; it would be due to precipitation hardening. The hardness was more increased with the increase of tungsten content and with the higher temperature of heating (within the range of below 600°C). For example, the hardness of 40% W-Ni alloy plating film heated at 600°C was HV 1075.
(2) The fact of hardening of W-Ni alloy plating films containing less than 30% of W was explained well by the laminated structure of cathode deposit consisting of alternate layers of Ni and W-Ni solid solution.
