Comparative study on the microstructure evolution of selective laser melted and wrought IN718 superalloy during subsequent heat treatment process and its effect on mechanical properties

The microstructure evolution of Inconel 718 (IN718) superalloy fabricated by selective laser melting (SLM) and wrought process during subsequent heat treatment process and their corresponding mechanical properties were comparatively studied in our work. After the same solution heat treatment at 1080 degrees C, the grain size of the SLM-IN718 keeps unchanged and also its dislocation subgrain structure is retained, whereas the grains of wrought IN718 is coarsened obviously. Due to the existence of dislocation subgrain structure and higher residual stress in the SLM-IN718 matrix, the precipitation of gamma '' strengthening phase is improved a lot during the subsequent aging process in the SLM-IN718 specimen compared to that in wrought IN718 specimen. Consequently, the hardness and strength of SLM-IN718 are significantly enhanced, which far exceed that of wrought IN718. By adjusting the aging treatment, the precipitation of gamma '' strengthening phase can be further optimized and the corresponding mechanical properties of SLM-IN718 are improved significantly. Especially, the elongation of SLM-IN718 at room temperature is significantly increased to 29% with only a little decrease in the strength.