Inconel 625 by Direct Metal Laser Sintering: Effects of the Process Parameters and Heat Treatments on Microstructure and Hardness

The aim of this study was to investigate the INCONEL® 625 (IN625) alloy processed by Direct Metal Laser Sintering (DMLS), showing the effect of different process parameters on the final density of the samples and analyzing the effects of different heat treatments on the microstructure and hardness. The results showed that there is a wide process parameter window for obtaining dense samples (with low porosity, < 0.25 %) with a fine cellular dendritic microstructure. IN625 processed by DMLS showed higher mechanical properties with respect to the same alloy after casting. Moreover, after aging treatments, carried out between 700 °C and 800 °C for 24 hours, the Brinell hardness (HBW) increased about 30% due to the precipitation of different phases. The FESEM analysis on heat-treated IN625 confirmed the presence of different precipitates such as gamma double prime (γ") phase, delta (δ) phase and other nanometric-sized phases. IN625 is generally used in applications that require high corrosion resistance from ambient to high temperature (up to 1000 °C). Therefore, the current research on heat-treated IN625 processed by DMLS could be useful for building components with high mechanical properties and high corrosion resistance in harsh environment.