This master thesis investigates the different effects of heat treatment on the microstructure of Alloy 718 manufactured with Powder bed fusion-Laser Beam (PBF-LB). The study focuses on assessing how different stress relief temperatures (ranging from 1065° C to 1155° C) and dwell times for each of the temperatures, (1 hour, 3 hours and 5 hours), influence the microstructure, grain size and hardness of the alloy 718.

The goal of this research is to identify the lowest temperature and dwell time combination that promote recrystallization.

The methodology started by subjecting the PBF-LB samples to various heat treatment conditions in temperature and time. Then the samples were then analysing though their microstructure using optical microscopy and Scanning Electron Microscopy (SEM). Also, grain size measurements and hardness tests were performed to assess the impact of heat treatment condition.

Key findings indicate that stress relief at 1095° C for 3 hours and 5 hours clearly transitions the microstructure from elongated grains to equiaxed grains, indicating the concrete start of recrystallization. The hardness of the material was found to decrease with increasing temperature, stabilizing between 190 to 250 HV.

The study concludes that the samples that went through 1095° C for 3 hours and 5 hours have the most desirable microstructure and mechanical properties in PBF-LB manufactured Alloy 718.