Tailoring the microstructure and mechanical properties of IN718 alloy via a novel scanning strategy implemented in laser powder bed fusion

The microsegregation of the brittle Laves phase at the interdendritic boundaries during additive manufacturing of IN718 leads to microvoid formation under tensile loads, thus, the mechanical properties are negatively affected. Recent advances have shown that extensive control over microstructural evolution is possible by modifying the additive manufacturing processes. Herein, it is aimed to tailor the final microstructure, managing the morphology of Laves phase, via implementing a novel scanning method, called time-homogenization (TH), in the laser powder bed fusion processing. Direct aging, solutionizing + direct aging, and homogenization + solutionizing + direct aging heat treatments were applied to increase the microstructural stability of additively manufactured IN718 at elevated temperatures. The modified microstructural features, microhardness, room and elevated temperature (550 °C and 650 °C) tensile properties of as-built and heat-treated specimens were systematically investigated considering the precipitation strengthening mechanism. Compared to the samples built by the standard scanning strategy (SP), fine and granular Laves phases were observed in TH specimens while SP specimens have coarse and chain-like Laves phases. Moreover, TH specimens after direct aging heat treatment exhibited an excellent combination of strength and ductility at room and elevated temperature.