Effects of Laser Power of Transition Layer on Microstructure Evolution and Wear-Resisting Self-Lubrication Behavior of Ni/Mo Composite Coating Prepared on Copper

Ni/Mo composite coating was prepared by laser cladding on copper surface to improve wear resistance. Because the melting point of Mo is 2620 degrees C, the range of available laser parameters is small, high laser power and slow scanning rate will cause the transition melting of Cu, and low laser power and fast scanning rate are difficult to reach the melting point of Mo. By optimizing the experimental parameters of Mo layer, the coating with good quality was obtained. The effects of laser power of transition layer on microstructure, hardness and tribological properties at room temperature and 500 degrees C were systematically studied. Meanwhile, the problems of non-wear resistance, non-ablative resistance and non-melting of Cu and Mo have been solved. The results show that the cladding layer consists of Mo, Ni3Mo, NiMo and Cu. The cladding layer is divided into transition layer and Mo-based layer. Due to the high thermal conductivity of Cu, the penetration crack of Mo layer can be suppressed by controlling the laser power of transition layer. With the increase of the laser power, when the laser power is 1500 W, the hardness of cladding layer is the highest, reaching 788.67 HV0.5, a minimum average friction coefficient is 0.456, and the wear rate is 6.4 x 10(-6) mm(3)/(N center dot m). When the laser power of the transition layer is 1600 W, the increase of Cu content leads to the decrease of hardness and wear rate. The NiO, CuO and MoO3 formed by Ni, Cu and Mo elements at 500 degrees C have good lubrication, and lead to the decrease of friction coefficients and the 11.4% reduction in the wear rate. The main wear mechanism at room temperature is abrasive wear, while at 500 degrees C the main wear mechanisms are abrasive wear and oxidative wear.