Effects of Substrate Preheating on Mechanical Properties of In718 Processed by Selective Laser Melting

Substrate preheating is a new way to affect the microstructure and material performance of IN718. Substrate preheating was investigated to reduce Niobium (Nb) segregation in the interdendritic region of IN718 superalloy and to improve mechanical properties through the selective laser melting (SLM) process. Here, we compared specimens built using 200°C (PH200) and 600°C (PH600) substrate preheating in an Ar atmosphere. The as-built PH200 and PH600 specimens had relatively similar grain morphologies and orientations along the building direction. The PH200 specimen showed a cellular structure and higher Nb segregation at the interdendritic region, whereas the PH600 specimen had a dendritic structure and lower Nb segregation. The amount of Nb segregation was much lower in the PH600 specimen, mainly due to the difference in cooling rate in the SLM process. The tensile properties, such as proof/tensile strengths and elongation, were slightly better in the PH600 specimen than in the PH200 specimen in both the as-built and heat-treated conditions. A clear difference was observed in creep, i.e., the PH600 specimen exhibited prolonged creep life and rupture-elongation compared to the PH200 specimen in both states. These differences between the PH200 and PH600 specimens mainly occurred due to differences of Laves and δ-phase fractions in the as-built and heat-treated conditions, respectively