Simultaneous strength and ductility improvement of As-cast HfMoTaTiZrCr x refractory high entropy alloys via Cr addition.

Overcoming the strength-ductility trade-off in refractory-based high-entropy alloys (RHEAs) is challenging. In this work, simultaneous strength-ductility enhancement of as-cast HfMoTaTiZrCr x refractory high-entropy alloys (RHEAs) was attained through Cr addition. Experimental results reveal that Cr addition induces a unique triphasic microstructure, comprising a Hf/Ti/Zr-enriched BCC1 phase, a Mo/Ta-dominated BCC2 phase, and a Cr/Mo/Ta-dominated C15-type Laves phase. The optimized HfMoTaTiZrCr0.75 alloy achieves σ0.2 of 1982.7 MPa (28% higher than Cr-free HfMoTaTiZr RHEAs) and ε f of 12.4% (65% enhancement), representing an outstanding strength among reported as-cast RHEAs with comparable ductility. Microstructural analysis suggests that the uniformly distributed BCC phase redistributes compressive stress and suppresses crack propagation, while the Laves phase enhances strength through Laves phase-induced dislocation obstruction.