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.