Tailoring of the Microstructure of Laser Powder Bed Fused Inconel 718 Using Solution Annealing and Aging Treatments

Inconel 718 (IN718) is a nickel-based superalloy with high weldability and is thus ideal for being processed via laser powder bed fusion (LPBF). Unlike traditional casting, LPBF IN718 develops a complex microstructure due to the rapid solidification that characterizes this manufacturing process. As a result, LPBF microstructures are different from those expected in equilibrium conditions, and for this reason, specific heat treatments should be designed. This paper, using differential scanning calorimetry (DSC), thermal mechanical analysis (TMA), and a field emission scanning electron microscope (FESEM), aims to develop a complete heat treatment that maximizes the material strength, thereby enhancing its microstructure. The paper shows that high-temperature annealing followed by two aging steps is the most suitable way to achieve the abovementioned task. More specifically, a complete dissolution of the delta phase via solution annealing at 1080 degrees C is the key factor in gaining an even and intense precipitation of gamma ' and gamma '' during the subsequent aging treatments. The microstructural analyses showed the elimination of needle-like delta particles and detrimental Laves phases. At the same time, intense precipitation of spherical and of discoidal reinforcing particles was achieved by performing the aging treatments at 720 and 630 degrees C, respectively.

Automated summary

The study focused on the heat treatment of Inconel 718, finding that a high-temperature annealing followed by two aging steps was the most suitable approach. By properly annealing and aging, detrimental microstructures were eliminated, and a uniform precipitation of reinforcing particles was achieved.