The effect of heat treatment on the microstructure of electroless Ni–P coatings containing SiC particles

Abstract Electroless Ni–P coatings containing SiC particles were co-deposited on SKD61 tool steel substrate. The effect of heat treatment on the microstructure of Ni–P–SiC composite coatings was investigated by X-ray diffraction and transmission electron microscopy. The presence of SiC particles did not affect the microstructure of the Ni–P alloy matrix when annealing temperature was below 400 °C. However, by increasing annealing temperature to 450 °C, SiC particles decomposed and reacted with nickel to form γ-Ni 5 Si 2 and β 1 -Ni 3 Si phases with a consequent free carbon precipitation. The structure of carbon was crystalline graphite with (0 0 0 2) preferred orientation and tended to aggregate while the amount of free carbon increased. On further annealing at 500 °C, phosphorus was incorporated into the Ni 5 Si 2 lattice, forming a Ni 5 (Si 1− x , P x ) 2 solid solution.