Effects of base plate temperature on microstructure evolution and high-temperature mechanical properties of IN718 processed by laser powder bed fusion using simulation and experiment

Abstract

Base plate preheating is a relatively new strategy to influence the mechanical properties and microstructure of IN718. Base plate preheating was studied to reduce Niobium (Nb) segregation in the interdendritic region of IN718 superalloy and to improve mechanical properties through the laser powder bed fusion (L-PBF) process. Here, we compared experimental results for high-temperature (650℃) mechanical properties of specimens built with 200℃ (PH200) and 600℃ (PH600) preheated base plates. 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 lower amount of Nb segregation in the PH600 specimen is mainly because of the cooling rate difference between specimens during the L-PBF process. The PH600 specimen exhibited slightly better tensile properties, longer creep life, and elongation than the PH200 specimen in both the as-built and heat-treated conditions. These differences mainly occurred due to differences in Laves and δ-phase fractions between the PH200 and PH600 specimens. The simulation result indicates that the temperature distribution in the block remains relatively uniform during the building process.