Origins of strength stabilities at elevated temperatures in additively manufactured refractory high entropy alloy

Abstract

While refractory high-entropy alloys (RHEAs) show promising potential for extreme applications, those directly fabricated via additive manufacturing methods have been hindered by their inferior mechanical properties, particularly at high temperatures. In this study, we successfully produced a Hf-Nb-Ti-V RHEA using directed energy deposition (DED) technique, achieving satisfactory tensile properties across a wide temperature range. This was accomplished by inducing severe lattice distortions in the fabricated RHEA, which can be traced back to the local chemical fluctuations present in the newly fabricated RHEA and the significant atomic radius mismatch. Due to strong solute pinning, these factors contribute to the superior yield strength of the DED-fabricated RHEA across a wide temperature range. Furthermore, the elastic constants in the fabricated RHEA show a negligible temperature dependence, revealed by first-principles calculations, ensuring satisfactory strengths even at high temperatures. This alloy design strategy, which involves introducing significant lattice distortion and maintaining the temperature-low sensitivity of the elastic moduli, opens up new possibilities for directly fabricating RHEAs with superior high-temperature properties.