Impact of multi-scale microstructural heterogeneities on the mechanical behavior of additively manufactured and post-processed Nb-based C103 alloy

Laser powder-bed fusion (LPBF) processed Nb-based alloy C103 (Nb-10Hf-1Ti wt.%) develops a complex, hierarchical microstructure comprising a fine-scale solidification cell structure, overlaid with a dense dislocation-network outlining the cell boundaries, within the primary grains. Additionally, sub-grain boundaries and a fine-scale dispersion of nano-sized hafnium oxide precipitates, possibly forming during solidification, decorate the solidification cell boundaries as well as exist within the cells. This complex hierarchical microstructure results in impressive tensile mechanical properties. Post-build stress-relieving annealing and hot isostatic pressing (HIP) largely annihilates the solidification cell structure and associated dislocation network, lowering the strength but with substantial recovery of tensile ductility. Nevertheless, the resulting microstructure offers higher strengths as compared to their wrought counterparts.