Effect of heat treatment on the microstructure evolution and mechanical behaviour of a selective laser melted Inconel 718 alloy

•This study aims to address the fact that after theselective laser melting (SLM) of an Inconel 718 alloy, the microstructures at each fabrication position are anisotropic due tothe coupling effect of multi-dimensional temperature gradient heat conductioncaused by the forming mode. Combined with the formation trends of eachphase in the Inconel 718 alloy, the microstructure evolution mechanism andcorresponding mechanical behaviour trends at each fabrication position underdifferent heat treatment regimes (including precipitation ageing (DA), δ ageing + precipitation ageing (SA) and high-temperature microstructure homogenization + δ ageing + precipitation ageing (HSA)) were studied.•At a low magnification (OM): with the continuous increasein the heat treatment temperature (DA→SA→HSA), the top/bottom/side surfaces ofthe heat-treated parts show a gradual decrease in and the disappearance of theprimary fabricated characteristic microstructure ("perlage" moltenpools and long strip molten channels) and the formation of and a significantincrease in recrystallization in turn (including a change of therecrystallization crystal structure from blurry to clear, an increase in thenumber of recrystallized grain boundaries and an increase in therecrystallization crystal size). Amongthem, the recrystallized grains are nucleated through the process oftemperature polygonization recovery and the grain boundary migration mechanism,and the further growth of the recrystallized grains is carried out by way ofannexation. Additionally, the grain boundary migration direction during recrystallization determines the orientation of the recrystallized grains.•At a high magnification (SEM, TEM): with thecontinuous increase in the heat treatment temperature (DA→SA→HSA), themicrostructures at different positions of each heat-treated sample graduallyevolve from anisotropic in the primary state (AB) to isotropic, in which theprimary crystal structure gradually changes from partially weakened to totaldisappearance, the corresponding degree of recrystallization changes from localto global, the unevenness inside the recrystallized crystal plane graduallybecomes even, and the corresponding depth of the recrystallized grain boundarybecame increasingly shallow. Additionally, with the continuous dissolution of alarge number of intergranular Laves phases precipitates in the primaryfabricated microstructure (AB) and the further uniform diffusion of solute fromintergranular to intragranular, the number