Effects of scanning strategies and heat treatments on the microstructure and mechanical performance of a Ni-based superalloy fabricated by laser powder bed fusion

The nickel-based superalloy has emerged as a leading candidate among existing aerospace alloys for laser powder bed fusion (LPBF) manufacturing. This study has explored the LPBF process of the SD-Ni03 superalloy, the design of which is based on the commercial alloy CM247LC, using three distinct scanning strategies. The mechanical performance of the resultant samples and the impact of heat treatment on SD-Ni03 were then examined. Our findings revealed anisotropic behaviour in the LPBF-fabricated samples, as evidenced by the variations in tensile properties between samples oriented parallel and perpendicular to the build direction (BD). Notably, SD-Ni03 samples fabricated with the zigzag-0°(Z0) strategy exhibited more pronounced anisotropy compared to those fabricated using the zigzag-90°(Z90) and island-90°(I90) strategies. Compared to the as-built (AB) samples, the ultimate tensile strength (UTS) values of heat-treated SD-Ni03-Z0 samples showed an increase of 24 % and −8% when tested parallelly or perpendicularly (respectively) to the BD at ambient temperature. At 900  °C, however, the UTS values decreased by 24 % and 23 %, respectively. Different heat treatment processes, including 5 different solution temperatures and 5 ageing temperatures, were applied to SD-Ni03-Z90 samples to investigate the effect of heat treatment on the volume fraction and morphologies of γ’ phases. The results indicated that solution treatment temperature mainly affected the size of the γ’ phase, while ageing treatment temperature mainly affected the volume fraction of γ’ phase. A remarkably high UTS value of 1597 MPa at ambient temperature was achieved through a solution treatment at 1070  °C for 2 h, followed by ageing at 750  °C for 24 h. The high UTS value could be attributed to the full precipitation and intermittent distribution of the primary γ’ and secondary γ’ phases. This study demonstrates that higher mechanical properties at 900  °C can be achieved in LPBF-fabricated precipitation-hardening alloys through direct ageing treatment.