Microstructure and mechanical properties of Hf-Nb-Ta-Ti-Zr refractory high-entropy alloys fabricated by laser directed energy deposition

The laser-directed energy deposition (LDED) additive manufacturing of Hf-Nb-Ta-Ti-Zr refractory high-entropy alloys (RHEAs) offers a pathway to achieving superior mechanical properties through microstructural control. This study systematically investigates the influence of laser power and scanning speed on grain size evolution, ranging from 38 μm to 143 μm, and correlates these variations with mechanical performance. Finite element (FE) modeling elucidates the thermal field distribution and its role in grain refinement. The findings reveal a strong interplay between microstructural morphology and mechanical properties, with the finest grain size (38 μm) exhibiting an optimal synergy of high yield strength (1123 MPa) and fracture elongation (12.0 %). Cellular structures enhance strength and ductility by restricting dislocation motion, whereas dendritic structures induce strain localization, leading to premature failure. In contrast, equiaxed microstructures homogenize deformation, improving ductility at the expense of strength. These insights establish a framework for optimizing LDED process parameters to tailor the microstructure and mechanical properties of high-performance RHEAs.