Abstract:Abstract: To improve the hardness and anti-wear properties of Ti6Al4V alloy, composite coatings were produced on the Ti6Al4V substrate under liquid nitrogen cooling by laser cladding 35wt.% WC/Ni60A. The microstructural evolution and mechanical properties of coatings under liquid nitrogen cooling were investigated. The phase compositions and microstructures were investigated by X-ray diffractometer (XRD), optical microscope (OM), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS), respectively. Sliding wear tests of the composite coatings under different cooling medium and substrate were conducted at 200N with the Si3Ni4 ceramic ball as the counter-body, and the corresponding wear mechanisms are discussed. The results indicated that the coatings both under liquid nitrogen cooling and under air cooling were mainly composed of α(Ti), WC, W2C, TiC, TiNi, Ti2Ni, TiNi3, NiB. Compared with the coating under air cooling , microstructure of the coating under liquid nitrogen cooling is uniform and dense, grain and precipitation phase is more small. The coating under liquid nitrogen cooling shows the sound metallurgical ( the bonding line) free pores and cracks between the coating and the substrate，and the microstructure near the bonding line shows more dense and fine directional solidification microstructure with a highly preferred orientation. The average microhardness of the coating under liquid nitrogen cooling is about 1363 HV0.2, which is 4 times higher than the Ti6Al4V substrate and is 1.61 times than the coating under air cooling. The relative anti-wear resistance of the coating under liquid nitrogen cooling is 5.39 times higher than the Ti6Al4V substrate and is 1.77 times than the coating under air cooling. Liquid nitrogen cooling can effectively improve the microhardness and anti-wear properties of coating.