Effect of Y_2O_3 on the sliding wear resistance of TiB/TiC-reinforced composite coatings fabricated by laser cladding

摘要

TiB/TiC-reinforced titanium matrix composite coatings were prepared by laser cladding on Ti6Al4V substrates. The effects of the addition of Y_2O_3 on the microstructure, microhardness, fracture toughness, and dry sliding wear resistance of the coatings were investigated. Microstructural observation showed that the coatings mainly consisted of TiC and TiB particles uniformly dispersed in the coarse cellular dendrites and interdendritic eutectic structure. The addition of Y_2O_3 refined the structure of the primary phase, improved the microstructural uniformity, and increased the volume fraction of TiC. The average microhardness of the coatings was improved from HV 725.30 to HV 812.98, and the average fracture toughness was increased from 8.32 MPa m~(1/2) to 17.36 MPa m~(1/2). The coating with Y_2O_3 had excellent resistance to micro-cutting and cracking. Analyses of the initial worn surfaces showed that the coating with Y_2O_3 was covered with a thin tribolayer, which consisted of Fe and its oxides. The true worn surfaces of the coating with Y_2O_3 were smoother than that of the coating without Y_2O_3 due to the protection by the tribolayer. Analyses of the cross-sections from the wear tracks revealed that the surface of the coating without Y_2O_3 was covered with many fine cracks which caused the debonding of the fragments from the surface of the coating. The wear mechanism of the coating with Y_2O_3 was defined as oxidative wear. Measurement results of the worn mass loss and friction coefficient values further verified the positive effect of Y_2O_3 on the improvement of wear resistance.