Achieving excellent ductility in a Hf–Nb–Ta–Zr refractory multi-principal-element alloy via electron-beam directional-solidification

Exploiting effective approaches to achieve superior ductility has consistently been a topic of widespread interest in refractory multi-principal-element alloys (RMPEAs). Herein, we developed a one-step forming method, electron-beam directional-solidification (EB-DS), to fabricate an equiatomic Hf–Nb–Ta–Zr RMPEA, and compared its microstructures as well as mechanical properties with those of the as-cast alloy fabricated by levitation induction melting. EB-DS method can transform the equiaxed grain microstructures in the as-cast alloy to columnar grain microstructures as well as eliminate the slight segregation. The room-temperature tensile test demonstrates that the ductility is substantially improved from 3.9% for the as-cast alloy to 23% for EB-DS alloy, accompanied by the slight enhancement in yield strength from 946 to 991 MPa. The microstructural investigations indicate that EB-DS alloys with columnar grains present a significantly optimized coordinated plastic deformation between the grain boundary region and the grain interior region, leading to the suppression of cracking along grain boundaries.