Hot-Cracking Mitigation and Microcrack Formation Mechanisms in Laser Powder Bed Fusion Processed Hastelloy X and Cantor High Entropy Alloys

The microcrack formation mechanisms and mitigation strategies were thoroughly investigated and explained in Hastelloy X samples fabricated via Laser Powder Bed Fusion (LPBF) with varying printing parameters and geometries. The microstructure evolution regarding microcrack formation is comprehensively examined in conjunction with thermal residual stresses affected by process parameters (e.g., laser power, scan velocity determining volumetric energy density, VED), proximity to build/substrate interface, and print section aspect ratio. Results indicated for microcracks to form in Hastelloy X, the VED must exceed the critical value of ~ 114 J/mm3, below which the lack-of-fusion porosity persists, thereby highlighting a trade-off with densification. Similar trends were also observed for a Cantor high-entropy alloy. Higher residual stresses near the print/substrate interface increase susceptibility to hot-cracking, leading to a higher density of microcracks at lower build heights along the Z-axis. A higher aspect ratio of the print section can further intensify the residual stresses, thus contributing to a higher density of microcracks as well as warpage in the bar sample. Finally, SEM observations and quantitative EBSD analysis establish a strong correlation between microcrack susceptibility, grain coarsening, and a Z-aligned grain/crystallographic texture, especially at higher VEDs or closer to the substrate. These findings provide insights for mitigating microcrack evolution and refining LPBF processes.

Graphical Abstract