Influence of Selective Laser Melting Process Parameters on Microstructure and Properties of a Typical Ni-Based Superalloy

The influence of selective laser melting (SLM) process parameters on the microstructure and mechanical properties of a typical Ni-based superalloy was researched. The optimum parameters of P = 170 W, V = 0.8 m/s were determined, under which the SLMed samples exhibited both the largest relative density of 99.57% and the best mechanical properties, including the microhardness (329.3 ± 3.8 HV), yield strength (726 ± 8.1 MPa), ultimate tensile strength (900 ± 5.9 MPa) and elongation ((31.9 ± 0.24)%). The average grain size ranges of SLMed samples are from 15.2 to 17.4 μm, with a typical mixed grain structure. Owing to the high cooling rate and remelting during SLM process, a large number of low-angle grain boundaries (LAGBs), dislocations and sub-grains were formed, and the fraction of LAGBs reached above 65%. At the same time, the content of low- Σ coincidence site lattice (CSL) boundaries was mostly less than 1%, while there was almost no γ ′ phase precipitated in the matrix. The texture of SLMed samples was weak, and there was no obvious preferred growth direction. Combining with the microstructure characterization, both grain refinement strengthening and dislocation strengthening were considered as the main strengthening mechanisms. Moreover, the fracture mechanism of the optimum sample belonged to ductile fracture.