Effect of post heat treatment on microstructure and mechanical properties of Ni-based composites by selective laser melting

Heat treatment is acknowledged to have a considerable effect on the microstructure and mechanical properties of selective laser melting (SLM) parts. In this study, heat treatments were conducted on SLM-processed WC/Inconel 718 composites with aim to obtain desirable mechanical properties. The microstructure, mechanical properties, and strengthening mechanisms under different treatments were investigated. The results showed that the microstructure became uniform with precipitates about 200 nm by dissolving carbides, and the grain size increased to 34.13 mu m with the decrease of high angle grain boundaries after treatments. The microhardness and tensile strength of the heat-treated composites were significantly increased, while the ductility was decreased. Homogenization plus double aging (HA) achieved the superior mechanical properties with microhardness of 487.74 HV, ultimate strength (sigma(b)) of 1313.16 MPa and elongation (delta) of 21.81%, increased by 27.5% in strength compared with the as-built composites (sigma(b) = 1029.71 MPa). The excellent performance benefited from the decreased crack sources, uniform precipitates, and low-angle grain boundaries.