The effect of heat treatment on the structure and abrasive wear resistance of autocatalytic NiP and NiP–SiC coatings

A systematic study on the relationships between the structure and abrasive wear resistance of autocatalytic nickel–phosphorus coatings (particle-free and SiC composite) with different phosphorus contents (i.e. 2.5–10.2 wt.% P) and under different thermal treatments (i.e. 300, 400 and 500°C) has been performed. The phase structure, composition and properties of the coatings could be controlled by changing the phosphorus content of the nickel–phosphorus matrix and by performing thermal treatments. The improvement in abrasive wear behaviour of the nanocrystalline (i.e. ≤6.0 wt.% P) coatings with heat treatment temperature up to 400°C was related to (i) the formation of a metastable equilibrium phase and (ii) precipitation of Ni3P compound. At higher thermal treatments (500°C), a change in the deformation mechanisms (Orowan mechanism) determined by the coarsening of Ni3P precipitates was associated with the decrease in abrasive wear resistance of the coatings. In addition, for the NiP–SiC coatings after annealing at 500°C, Ni3Si was formed and the adhesion between the reinforcement and the matrix was enhanced.