Additive manufacturing (AM) technology offers the possibility to produce engineering metal components with superior mechanical properties, compared to those of traditional casting or wrought materials. However, in order to use these materials in aeroengines, they need post-treatment to reduce residual stresses and homogenize their microstructure. This process aims to precipitate desirable phases such as carbides and borides, and eliminate undesired ones such as Laves phase, which causes embrittlement at high temperature.
In the present study, a series of tensile tests at 650 °C were performed on LPBF-printed in718 under different homogenization treatment conditions. The samples were scanned using an SEM to obtain images of the microstructure, and the kernel average misorientation (KAM) map was used to quantify the degree of elongation of the test specimens. The results showed that the as-printed condition exhibited the lowest strength, but the highest ductility, as compared to the post-heat-treated conditions. The high ductility of the as-printed in718 is attributed to the fact that the grains are oriented parallel to the printing and tensile loading directions, which allows the dislocations to move easily through the low-angle grain boundaries during deformation.
Increasing the homogenization treatment time led to a drop in both the tensile and yield strength and ductility of the in718, owing to the increased content of the g' and g''' phases in the g-matrix and annihilation of dislocation density due to the coarsening of the MC carbide particles on the grain boundaries. The DRX process became dominant only in the 1 h homogenized conditions HSA1 and HSA2, where a high density of the primary dislocation network is preserved along with an accelerated precipitation of d-phase at the grain boundaries.
