A novel AlMoNbHfTi refractory high-entropy alloy with superior ductility

Abstract

Refractory high-entropy alloys (RHEAs) have attracted considerable attention in the recent pastdue to their high yield strength (YS) and superior high-temperature mechanical properties. However, poor ductility at room temperature and high density are still major challenges in their processing and industrial application. Here, two novel single-phase body-centered cubic (BCC) structured Al5MoxNb36Hf13Ti46-x (x = 5, 7 at%, marked as Mo5 and Mo7) RHEAs with excellent room-temperature ductility and low density (7.53–7.64 g/cm3) were designed and prepared by tailoring the Mo content. These two RHEAs have a good combination of ambient ductility, high YS, and low density. The as-cast state Mo5 and Mo7 alloys show ∼ 20%, ∼ 15% tensile ductility and 680, 820 MPa YS, respectively. The YS increased to 892 MPa for the Mo5 alloy and up to 900 MPa for the Mo7 alloy after cold rolling and heat treatment, respectively. The peak strength at 873 K increased from 666 MPa of the Mo5 alloy to 710 MPa of the Mo7 alloy, and the peak strength of the Mo7 alloy at 1073 K was higher than 450 MPa. According to the solid solution strengthening model, the high strength can be attributed to the atomic radius misfit and shear modulus misfit of the alloy components, as well as high atomic-level pressure. Increasing the Mo content will introduce a solid solution strengthening effect into the RHEAs. The large tensile ductility arises owing to the dense dislocation slip and no twins or the second phase was detected in the tensiled sample. This study provides more helpful information to design RHEAs with superior ambient tensile ductility.