Grain Growth During Keyhole Mode Pulsed Laser Powder Bed Fusion of IN738LC

Minimising hot cracking during laser powder bed fusion (LPBF) of difficult-to-weld alloys is an essential step for LPBF to be applied more widely. In this study, using a pulsed LPBF machine, grain growth during keyhole mode LPBF of IN738LC has been studied. Measurements have shown that the < 100 > growth direction can differ significantly from build direction to provide an effect of limiting crack length, depending on the scan direction. Without the change in scan direction after each layer, grains grew in long and lamellar-alternating form of a thin {100} grain and a wide non-{100} grain. Long hot cracks have been found to grow normal to the scan direction, likely relating to the thermal stress developed during solidification of the long melt tracks. The use of a scan strategy of 67 degrees change has been found to disrupt grain growth in lamellar form, and thus has enabled a strong effect on limiting the crack length.