Microstructure and mechanical properties of laser welded PBF-LB/IN718

Abstract

Applications for additively manufactured (AM) metal parts, particularly via laser-based powder bed fusion (PBF-LB/M), have been growing significantly in industries with high level of requirements such as aerospace, nuclear plant, automotive, energy, and medical industry. However, PBF-LB/M parts often require welding to other components due to their limited size. Thus, the weldability of PBF-LB/M parts is of interest, particularly due to the microstructural differences between PBF-LB/M and conventionally manufactured parts. This study investigates the microstructure and mechanical properties of laser-welded PBF-LB/IN718 and compares the results with laser-welded sheet metal IN718. In addition, the effect of heat treatment before welding on the weldability of PBF-LB/IN718 samples was evaluated. Both the heat-treated and as-built PBF-LB/IN718 welds had lower microhardness at the fusion zone (FZ) than the base metals, whereas the sheet metal IN718 weld showed higher microhardness at FZ than the base metal. This was attributed to the distinct secondary phases and microstructure of the conventional IN718 and PBF-LB/IN718 samples. Nevertheless, the ultimate tensile strength and yield strength of PBF-LB/IN718 welds were higher than the conventional IN718 welds, proving that laser welding is a viable method of joining PBF-LB/IN718 parts. Finally, the fatigue strength of the PBF-LB/IN718 welds, assessed at 106 cycles, was inferior to that of the conventional IN718 welds, owning to the defects such as lack of fusion in the base metal of PBF-LB/IN718 samples.