Laser Cladding ZrV₂O₇/SiC/Ni Composite Coating

With the rapid development of high-speed railway in China, high-speed vehicles bear very large load when braking and the existing brake disc cannot satisfy the requirements, which retard the development of the vehicles. The composite coating used on the brake disc surface may have good hardness, wear resistance and resistance to high temperature performance. In this paper, the ZrV₂O₇/SiC/Ni composite coating prepared by laser cladding technology has important theoretical significance and great engineering application value.Firstly, the powders of negative thermal expansion material ZrV₂O₇ with high purity was prepared by wet chemical, hydrothermal and water bath methods in this paper. Effects of calcination temperature and preparation method on their purity and morphology were studied. The phase structure, morphology and composition of the powders were characterized by using X- ray diffraction（XRD）, scanning electron microscopy（SEM） and energy dispersive spectroscopy（EDS） respectively. The results show that the purity of ZrV₂O₇ powders prepared by hydrothermal and wet chemical methods is high, and the preparation efficiency is high by hydrothermal method. When the sintering temperature is 750℃, the purity of ZrV₂O₇ powders prepared by hydrothermal method got the best, 97.95%.Second, by the use of the ZrV₂O₇ as raw material, ZrV₂O₇/SiC/Ni coating on 45 steel surface was prepared by laser cladding technology. Using X- ray diffraction, metallographic microscope, scanning electron microscope, energy spectrometer, micro-hardness tester and wear testing machine, the morphology, microstructure, phase composition, hardness and wear resistance of laser cladding alloy powders were studied, respectively. The results show that when the laser power is 1200 W, defocusing distance is 268 mm, scanning speed is 300mm/min, the coating has good macro-morphology. When ZrV₂O₇ is added to the cladding alloy powder, the pores and the cracks in cladding coating is significantly reduced. With the increase of the mass fraction of ZrV₂O₇, the micro-hardness and the abrasion resistance of the coating gets the peak value, and the friction coefficient has the minimum value. When the mass fraction of 12wt% is ZrV₂O₇, the micro-hardness and the abrasion resistance of the coating are 2.59 times and 12.5 times higher than those of the substrate material, espectively; the friction coefficient is minimum, which is 0.71 times that of the substrate material, and the wear mechanism of the coating is mainly the grain wear mechanism.