The failure mechanism of 50% laser additive manufactured Inconel 718 and the deformation behavior of Laves phases during a tensile process

The 50% laser additive manufactured (50%LAMed) tensile samples of Inconel 718 superalloy, i.e., the laser-deposited zone and the substrate zone, occupied 50% volume fraction respectively along the tensile direction, have been fabricated by using laser additive manufacturing (LAM) technology. The inter-dendritic Laves phases were reserved because solution heat treatment could not be used in case of the deteriorating mechanical properties of a forging substrate. Meanwhile, most of the γ″ phases were precipitated in the inter-dendritic area, leading to local stress concentration around the Laves phases in the process of a tensile test. With tensile stress increasing, the degree of deformation and fracture of the Laves phases was closely related to the morphologies of themselves. For the long striped Laves phases, in order to deform with the austenite matrix, they slipped and broke up into small parts. For most of the granular Laves phases, they did not break up and held original morphologies in the process of the tensile test. The broken Laves phases were separated from the γ matrix, and micropores formed at the surface between them. The fracture mechanism was the microvoid coalescence ductile fracture, and the Laves phases were the main nucleuses for the formation of micropores. This study indicates that the mechanical properties of 50%LAMed Inconel 718 can be improved by controlling the morphologies of the Laves phases.