The study of interdiffusion phenomena of NiP/steel interface

Abstract

Electroless nickel (EN) coating is a binary alloy of nickel and phosphorus whose content in phosphorus varies between 3 and 14 wt% depending on the bath composition and deposition conditions. Heat treatment is one of the most important factors affecting the properties of EN coating. In most applications, EN coating is used in as-plated form. For wear-resistant applications, however, hardness and wear resistance of the EN layer can be improved by heat treatment. As indicated in the literature, EN deposits can reach a peak hardness by heat treating under an inert atmosphere for one hour at 400[degree]C(1-9). At temperatures above 600[degree]C, counterdiffusion of nickel and iron occurs, across the plating/substrate boundary, for EN deposited steel. Consequently, on one hand, a diffusion layer is formed between the deposit/substrate interface and better adhesion of the EN coating to the steel substrate is expected. On the other hand, it could also be detrimental to adhesion if intermetallic compounds appear. The interdiffusion between iron and nickel has been investigated extensively in the literature; however, the role of phosphorus in the diffusion process is still not well known. This article focuses the interesting effect of phosphorus on the interdiffusion of the Ni-P/steel interface.