Deformation behavior of selective laser-melted Inconel 718 superalloy

We report a detailed study of the deformation behavior of SLM-built Inconel718 (IN718) alloy during uniaxial tensile deformation. It can be found that a constant drop in the strain-hardening rate prior to necking initiation leads to the poor plasticity of SLM-built IN718 alloy. Through carefully examining the strain hardening mechanism and damage evolution, it can be identified that the decreased rate of the strain hardening rate in the second hardening stage is attributed to the initiation of micro-voids during plastic deformation. The damage of as-built and DA specimens during the tensile process mainly encompasses the separation of Laves phase (carbide) and matrix, grain boundary cracking, and the fracture of long Laves phase, while the damage of HA specimens mainly includes the separation of carbide and matrix and grain boundary cracking. A multi-scale model was employed to analyze the effects of Laves phase and strengthening phase on the ductility of IN718 alloy. The model calculation indicates that the volume fraction, cracking fraction, and shape factor of the Laves phase, as well as the volume fraction of strengthening phase, have significant effects on the ductility. The strain hardening rate of SLM-built IN718 alloy decreases more rapidly than that of forged IN718 alloy due to a large number of microscopic defects and grain boundary cracks. Our research advocates the perspective of helping guide future innovations towards a synergy between high strength and high ductility for SLM-built IN718 alloy.