Effect of linear energy density on microstructure and wear resistance of WC-Co-Cr composite coating by laser cladding

Abstract

To improve the wear resistance of titanium alloy, the WC-reinforced composite coatings were prepared on Ti-6Al-4V substrate by laser cladding. The effect of linear energy density (LED: 73.3 J·mm−1-283.3 J·mm−1) on the microstructure, microhardness and wear resistance of the composite coatings were investigated. The evolution of WC during laser cladding was revealed and discussed. It is found that the WC is dissolved by the forms of releasing W and C with increasing LED, and grows into specific shapes according to the Lifshitz-Slyosov-Wagner model. As the LED increases, the retention index of WC decreases (0.91–0.80) and the grain size increases (1.89 μm–5.81 μm) in the composite coating. The microstructure differences lead to the microhardness and brittleness increasement of composite coating. Compared with the Ti-6Al-4V substrate, the maximum microhardness improvement and wear mass loss reduction are 5 times and 25 times by varying LED. The main wear mechanism of composite coatings is abrasive wear. However, additional forms of wear mass loss such as adhesive wear and WC peeling can occur due to LED variation, and further leads to the difference in wear resistance. It is expected that the evolution of WC, which can regulate the microstructure will provide an effective theoretical foundation for the wear-resistance improvement of the laser cladding coatings.