Microstructure, fatigue, and impact toughness properties of additively manufactured nickel alloy 718

A complete understanding of processing-structure-property-performance relationship of additively manufactured (AM) components are critical from an application standpoint. Therefore, in the current investigation, a comprehensive microstructural characterization and mechanical properties (tensile, fatigue and impact toughness) evaluation of nickel alloy 718 AM by the laser powder bed fusion (L-PBF) technique have been performed. AM builds were made from powders manufactured via different atomization conditions. Although the standard post-heat treatment procedure led to the removal of severe interdendritic segregation both grain boundary and intra-grain precipitation of δ phase occurred. Regardless of δ phase presence, axial fatigue properties of both the AM builds were similar to design handbook wrought fatigue data. However, due to the δ phase, impact toughness properties were comparable to the wrought material conditions that exhibited δ phase. Fractured surfaces of Charpy impact samples exhibited crack propagation extensively along the boundaries decorated by δ precipitates.