Effect of micro/nano-SiCP on microstructure and properties of electroless Ni-P-SiCP composite coatings

Ni-P-SiCP coatings were deposited on 42CrMo steel by electroless plating. The surface morphologies and phase structures of the Ni-P-SiCP coatings processed under different SiCP concentrations at different heat treatment temperatures were analyzed. The microhardness, corrosion resistance, and wear resistance of the Ni-P-SiCP coatings were studied. Results show that Ni-P-SiCP coatings exhibit cauliflower-like morphology. Increasing the SiCP concentration can reduce the size of cellular structure. The microhardness and corrosion resistance are initially increased and then decreased with the increase in SiCP concentration. The maximum microhardness and corrosion potential are 7379 MPa and −0.363 V, respectively, when the SiCP concentration is 5 g/L. The Ni-P-SiCP coatings exhibit an amorphous structure, and the width of the diffuse diffraction peak becomes narrower with the increase in SiCP concentration. It is suggested that SiCP inhibits the deposition of P and promotes the microcrystalline transformation. After heat treatment at 350 °C, the Ni-P-SiCP coatings are crystallized, resulting in the precipitation of Ni3P phase. Heat treatment at 400 °C for 1 h maximizes the structure. The synergistic effect of the Ni3P precipitate phase and SiCP dispersion phase promotes the densification of the cellular structure, leading to the optimal microhardness (13 828 MPa), optimal corrosion resistance (−0.277 V), and excellent wear resistance. The wear mechanism is dominated by micro-cutting abrasive wear with slight adhesive and oxidative wear.