Abstract:Ni-P alloy coatings with good adhesion and wear resistance were prepared on the surface of titanium alloy TC4 substrate using an electroless plating method. The structures of coatings after heat treatment at different temperatures were investigated by means of SEM, XRD and EDS. Furthermore, the relationship of different heat treatment temperatures, coating structure, coating hardness and wear resistance was established. The results show that the combination of double zincating and heat treatment can significantly improve the adhesive strength in the coating/substrate interface, and the adhesion of the coating reaches 35 N after heat treatment at 600 °C for 1 h. Hardness HV and wear loss of the substrate are 3780 MPa and 9.6 mg, respectively, while the hardness HV and the wear loss of the coating as plated are 5760 MPa and 7.7 mg, respectively, which indicate that electroless Ni-P coating can enhance hardness and wear resistance of TC4 titanium alloy. With the increase in temperature of heat treatment, Ni3P phase increases. The hardness shows higher values in the presence of Ni3P phase with highly-dispersed distribution, reaching the highest of 9790 MPa. Further increase in temperature results in the segregation of Ni3P phase and slowdown of dispersion degree, suggesting the hardness reduction. Wear loss of the coating decreases with increasing heat treatment temperature, revealing the wear resistance increases with the rise of heat treatment temperature. After heat treatment at 600 °C, despite the bigger grains and lower hardness of the coating, the best crystal integrity is produced, and the plasticity and the toughness of the coating are increased, so the coating shows the best wear resistance.