Effect of Heat Treatment on Microstructure and Mechanical Properties of Additively Manufactured Inconel 718 alloy Optimized Using a Modified Taguchi Method

This study optimizes Selective Laser Melting (SLM) parameters for Inconel 718 (IN718) using a modified Taguchi approach and investigates the effects of heat treatments and build orientations (XY and XZ) on the mechanical properties. Experiments were performed with constant hatch distance (0.11 mm) and powder bed thickness (0.04 mm), while laser power (300–400 W) and scanning speed (520–1400 mm/s) were varied. The modified Taguchi’s method was employed for selecting optimal parameters, a laser power of 360 W and scanning speed of 960 mm/s yielded the best mechanical performance. In the as-printed condition, IN718 exhibited a yield strength (YS) of 774 ± 96 MPa, ultimate tensile strength (UTS) of 1141 ± 81 MPa, elongation (%El) of 31 ± 10%, and hardness of ~ 355 HV. After solution treatment and aging (STA), the strength increased significantly (YS = 1286 ± 129 MPa; UTS = 1516 ± 130 MPa, and hardness = 535 HV), while elongation decreased to 22 ± 4% due to γ′/γ″ precipitation hardening. Hot isostatic pressing followed by STA resulted in slightly reduced strength (YS = 1163 ± 171 MPa; UTS = 1444 ± 64 MPa; %El = 21 ± 3%), attributed to grain coarsening during HIPing. Build orientation influenced anisotropy: XY builds exhibited higher strength and hardness (~ 535 Hv), XZ builds showed higher ductility up to 20–25%. Microstructural analysis revealed porosity and columnar grains in as printed samples, strengthened columnar structures after STA, and equiaxed recrystallized grains after HIP + STA. Overall, the combination of optimized SLM parameters and suitable heat treatments enables the fabrication of dense, defect-free IN718 components with superior mechanical properties for aerospace applications.