The Study on Hardness of Non-electrolytically Plated Ni-P Deposits at High Temperatures and the Effects Given by Heat-Treatments

Abstract

It is well known that the hardness of non-electrolytically plated Ni-P deposits may be so varied by heat-treatments that it is very high when treated at a suitable temperature. However, the hardness at high temperatures has never been measured.
In these experiments, the hardness at each high temperature during heating or cooling was measured with Micro Vickers Hardness Tester for high temperatures. The material used for substrate was steel of 0.5% C. As the results, maximum points of hardness were confirmed at 250 and 400°C. When the deposits, treated at above 400°C, were reheated, they showed a tendency to softening; while those, treated at lower temperatures, showed rehardening at about 400°C when they were reheated.
The samples of deposits were always more than 8μ in thickness as the results of preliminary investigation of the relation between depositing conditions and thickness or hardness.
Composition of the bath in these experiments was as follows:
NiCl₂⋅6H₂O 30g/l
NaH₂PO₂⋅H₂O 10g/l
Na₃C₆H₅O₇⋅2H₂O 15g/l
NaC₂H₃O₂⋅3H₂O 5g/l