The effect of carbides on the creep performance of Hastelloy X fabricated by laser powder bed fusion

The creep property is the decisive criterion for the high-temperature application of Hastelloy X (HX alloy) and the carbides have been reported to play an important role in the creep performance of conventionally manufactured HX alloy. However, their impact on the creep performance of HX alloys fabricated by laser powder bed fusion (LPBF) remains to be explored. In this study, two different post-treatments were designed and applied to LPBF HX alloy to create microstructures with different carbide distributions at the grain boundaries (GBs). By systematically comparing grain structures before and after creep, the results revealed that GB sliding was activated at 815 °C, while it is not operative at 650 °C. On this basis, the high amount of GB carbides improved creep lifetime by 2 times at 815 °C via inhibiting GB sliding, while they revealed a negligible impact on creep lifetime at 650 °C. If dislocation-based deformation is operative, the depletion in solutes of the matrix via carbide formation reduces creep resistance unfavourably. These findings provide strategies for further optimization of the creep response of carbide and solid solution strengthened Ni-base alloys.