Microstructure and mechanical properties of in-situ MC-reinforced CoCrMoNbTi high-entropy alloy coating by laser additive manufacturing

Abstract

In situ carbides (TiC/Cr7C3) reinforced CoCrMoNbTiC0.2 high-entropy alloy coatings were prepared on the Ti-6Al- 4V titanium alloy substrate by laser melting deposition technology. Effect of the laser power on the surface morphology, phase consistent, microstructure and microhardness were investigated. The results show that the coatings were composed of a simple BCC solid solution and a small amount of TiC and Cr7C3 carbides. The in-situ MC (TiC/Cr7C3) carbides were evenly distributed in the BCC matrix. The laser power has a significant impact on the forming quality and mechanical properties of the coatings. As the optimal laser power of 1500 W were applied, the coating mostly free of defects exhibited a fine dendritic microstructure. With the increasing laser power, the microhardness of the coatings was first increased and then decreased gradually. The highest microhardness of the coating (1500 W) was up to 650 HV0.5, which was 2 times higher than that of the substrate. The excellent mechanical properties of the coatings were attributed to the synergetic effects of the second phase strengthening, solid solution strengthening and fine microstructure.