Origin of the enhanced ductility in additively manufactured Nb40Ta25Ti15Hf15Zr5 refractory high-entropy alloy

Refractory high-entropy alloys (RHEAs) are promising for high-temperature applications but suffer from segregation and limited ductility when cast. Herein, a crack-free Nb40Ta25Ti15Hf15Zr5 RHEA was successfully fabricated using laser-directed energy deposition (LDED) with a layer-by-layer remelting strategy, effectively melting and alloying elemental powders with dramatically different melting points. Compared to its as-cast counterpart with equivalent yield strength (~747 MPa), the AM-processed alloy demonstrated a remarkable 70% enhancement in tensile elongation (14.8% vs. 8.7%). Microstructural analysis revealed that the rapid solidification during AM introduced a high density of initial dislocations containing numerous jogs and loops. These pre-existing dislocations were found to actively promote cross-slip and multiplication of screw dislocations during deformation, leading to superior strain hardening and more uniform plastic flow. This work highlights the critical role of AM-generated dislocations in activating favorable deformation mechanisms, and provides a new avenue for designing ductile RHEAs via additive manufacturing.