Enhancing mechanical properties of quasi-continuous-wave laser additive manufactured Inconel 718 through controlling the niobium-rich precipitates

Abstract

Controlling of Nb-rich intermetallics is an important topic for laser additive manufacturing (LAM) of Inconel 718. In the present work, a novel quasi-continuous-wave LAM (QCW-LAM) with different pulse frequencies is used to control the morphology, distribution and amount of Nb-rich phases of Inconel 718. The results show that dispersively distributed Nb-rich Laves phases are produced by introducing equiaxed dendrites at a low pulse frequency while a high pulse frequency results in coarse and chain-like Laves phases. The samples featured by fine and discrete Laves phases show a good response to the post solution-aging treatment in which the dissolution of Laves-phase and subsequently discrete precipitations of δ-phase as well as high-density precipitation of γ″-Ni3Nb strengthening phase are promoted. Thus, a good combination of strength and ductility is achieved for the QCW-LAM fabricated Inconel 718. This study shows a desired mechanical property can be obtained by synergistically optimizing the microstructures in which various Nb-rich phases are involved even though the formation of brittle Laves phases is hardly avoided during LAM of Inconel 718.