Microstructure and surface properties of WC reinforced Ti6Al4V composite coating by laser direct deposition

Abstract

WC particle-reinforced Ti6Al4V composite coatings were prepared on Ti6Al4V substrates by laser direct deposition using Ti6Al4V alloy powders containing 3 wt%, 6 wt% and 9 wt% WC. The microstructure and properties of the deposited coatings with different WC additions were studied separately using metallographic microscopy, scanning electron microscopy, X-ray diffraction, microhardness tests, abrasion tests, and electrochemical workstation. The results showed that the composite coatings with WC addition were mainly composed of α-Ti, β-Ti, unmelted WC and in-situ produced new phases such as TiC, W₂C and (W,Ti)C_1-x. A reaction layer composed of W₂C and TiC was formed on the periphery of WC. The formation of high microhardness strip and block α-(Ti,N) interstitial solid solution at the top of the coatings was attributed to the occurrence of N-rich regions by N element segregation. The N element and unmelted WC played important roles in improving the microhardness and wear resistance of coatings by in-situ solution strengthening and refining microstructure, respectively. Compared with the Ti6Al4V substrate, the average microhardness of the coating with 6 % WC addition increased by about 57.8 %, the wear rate decreased by 72.1 %, and the roughness of the worn surface was the smallest. Moreover, the addition of WC has little contribution to improving the corrosion resistance of the coating, only the coating with 6 % WC has better corrosion resistance compared with the Ti6Al4V substrate. Therefore, 6 % WC is the optimal addition amount for improving coating performance.