Effect of Al on Microstructure and Mechanical Properties of ATI 718Plus by Laser Additive Manufacturing

To clarify the mechanism of the role of Al element in the additive manufacturing of Ni-based superalloys, ATI 718Plus alloys with varying Al contents (1, 3, and 5 wt%) were fabricated using the laser additive manufacturing and the effects of Al content on the microstructure and mechanical properties were systematically analyzed. The experimental and CALPHAD simulation results show that with the increase in Al addition, the freezing range of the alloys was lowered, but this has a paradoxical effect on the susceptibility of the alloy to hot-tearing and solid-state cracking. The addition of Al increased the γ′ and Laves phase volume fractions and suppressed the precipitation of the η phase. Simultaneously improving γ/γ′ lattice misfits effectively promoted the transformation of γ′ phase from spherical to cubic. The precipitation of NiAl phase in the 5 wt% Al-added alloy was determined, the formation mechanism of NiAl phase was analyzed, and the solidification sequence of the precipitated phase in the alloy was summarized. In addition, with the increase in Al addition, the microhardness of the alloy increased gradually, the tensile strength increased at first and then decreased, but the plasticity deteriorated seriously. The insights gained from this study offer valuable theoretical guidance for the strategic compositional design of additively manufactured Ni-based superalloys destined for deployment under extreme conditions.