Interdiffusion of the Electroless Ni-P Deposit with the Steel Substrate

The diffusion between carbon steel substrate and the electroless Ni-P deposit were investigated with SEM-EDX and TEM for the microstructure of the diffusion layer and the diffusion kinetics. Phosphorus is excluded from the diffusion layer while nickel dissolves in iron to give the alpha-Fe phase. The diffusion layer grows parabolically with respect to time, and is strongly governed by temperature. The diffusivities were estimated with the Boltzmann-Matano method to show that the diffusion enroutes grain boundary at temperatures below 690°C while it enroutes lattice at higher temperatures. The activation energies for these two diffusion paths were estimated from the Arrhenius plot.