Densification and microstructural investigation of Inconel 718 parts fabricated by selective laser melting

In this study, the densification behavior and microstructural development of Inconel 718 parts fabricated by selective laser melting (SLM) were investigated with variation of the applied laser scanning speed. The starting materials of Inconel 718 powder particles were prepared using a gas atomization process showing uniform size distribution with high flowability. During the SLM process, the applied scan speed played a decisive role in densification during the SLM process, and that the highest density (>99%) and hardness (320 Hv(0.5)) could be achieved at the laser scanning speed of 800 mm/s. Upon fabrication, the microstructure of Inconel 718 parts was characterized by the presence of columnar grains, due to the rapid rate of cooling of the molten pool. These grains, in particular, in XZ and YZ planes, were observed to be parallel to the building direction (Z-axis), with size ranging from several to hundreds of micrometers. It was also found that the fine cellular substructures, within the specified range between 0.5 and 1 mu m, were embedded inside each large grain with low angle boundaries (<2 degrees). The experimental findings in this study may provide fundamental understanding of densification and microstructural characteristics induced by the laser melting process.This study was supported financially by Fundamental Research Program of the Korean Institute of Materials Science (KIMS). This work was also supported by the National Research Council of Science & Technology (NST) grant by the Korea government (MSIP), (No. CRC-15-03KIMM)