Tailoring nanoprecipitates to enhance strength-plasticity synergy in HfZrTiTa_(1-x)Al_x refractory high-entropy alloys

In this study, HfZrTiTa_(1-x)Al_x refractory high entropy alloys (RHEAs) were developed by tailoring nanoprecipitates to overcome the brittleness of typical HfZrTiTa RHEA. Microstructure and mechanical properties of HfZrTiTa_(1-x)Al_x RHEAs were investigated systematically. Experimental results show that a body-centered cubic (BCC) matrix and severe component segregation were observed in designed RHEAs. The nanoprecipitates with Zr₂Al intermetallic occurred in Ta_0.5Al_0.5- Ta₀Al₁ RHEAs, and the density of nanoprecipitates is increased with an increase of Al content. The average grain sizes are increased with an increase in Al content. The RHEAs have high hardness with ranging from 389 Hv to 620 Hv and high compressive yield strength from 1160 MPa to 1677 MPa. Among the designed alloys in this study, the HfZrTiTa_0.5Al_0.5 RHEA had the best combination between yield strength (1160 MPa) and plasticity (fracture strain of 28.6%) in the designed alloys. Thermodynamic parameter calculation predicted the designed RHEAs with more negative mixing enthalpy are easier to form nanoprecipitates with Zr₂Al intermetallic phase, which agrees with the experimental results. The nanoprecipitates effectively increase the resistance to dislocation glide and further improving strength of HfZrTiTa_0.5Al_0.5. The multiple dislocation slips induced by nanoprecipitates contributed to the excellent plasticity of HfZrTiTa_0.5Al_0.5. The regulation of nanoprecipitates by optimizing composition is demonstrated to be an effective method to enhance the strength–plasticity synergy of HfZrTiTa_(1-x)Al_x RHEAs.