Effects of powder forming method and heat treatment process on microstructure and mechanical properties of ATI 718Plus alloy by laser additive manufacturing

ATI 718Plus alloy powders were prepared by vacuum induction melting gas atomization (VIGA) and plasma rotating electrode preparation (PREP) methods. Effects of direct aging (DA) and homogenization-solution-aging (HSA) heat treatment processes on microstructure and mechanical properties of the alloy prepared by laser additive manufacturing (LAM) utilizing various powders mentioned above were systematically studied. The LAM process parameters such as laser power and scanning speed were optimized by orthogonal experiment. The results indicate that the porosity of the samples fabricated with PREP powder is controlled below 0.05%. In addition, after DA treatment, a large number of nano-sized γ′ phases are precipitated in the interdendritic and dendritic trunk regions, but the Laves phase is not significantly affected. After HSA treatment, the Laves phase is basically eliminated, and a large number of needle-like η phases precipitate along the grain boundaries, but the grains undergo obvious coarsening compared to that by DA treatment. The tensile results show that compared to the as-deposited samples, the ultimate tensile strength and elongation of the HAS-treated samples are significantly improved, reaching (1,245±2.6) MPa and (28±2.7)%, respectively. The tensile strength of DA samples significantly increases to (1,296±8.3) MPa, and the elongation slightly decreases to (17.6±2.25)%.