Superior mechanical properties and strengthening mechanisms of lightweight AlxCrNbVMo refractory high-entropy alloys (x = 0, 0.5, 1.0) fabricated by the powder metallurgy process

Abstract

Light and strong AlxCrNbVMo (x = 0, 0.5, and 1.0) refractory high-entropy alloys (RHEAs) were designed and fabricated via a the powder metallurgical process. The microstructure of the AlxCrNbVMo alloys consisted of a single BCC crystalline structure with a sub-micron grain size of 2−3 μm, and small amounts (< 4 vol.%) of fine oxide dispersoids. This homogeneous microstructure, without chemical segregation or micropores was achieved via high-energy ball milling and spark-plasma sintering. The alloys exhibited superior mechanical properties at 25 and 1000℃ compared to those of other RHEAs. Here, CrNbVMo alloy showed a yield strength of 2743 MPa at room temperature. Surprisingly, the yield strength of the CrNbVMo alloy at 1000℃ was 1513 MPa. The specific yield strength of the CrNbVMo alloy was increased by 27 % and 87 % at 25 and 1000℃, respectively, compared to the AlMo0.5NbTa0.5TiZr RHEA, which exhibited so far the highest specific yield strength among the cast RHEAs. The addition of Al to CrNbVMo alloy was advantageous in reducing its reduce density to below 8.0 g/cm3, while the elastic modulus decreased due to the much lower elastic modulus of Al compared to that of the CrNbVMo alloy. Quantitative analysis of the strengthening contributions, showed that the solid solution strengthening, arising from a large misfit effect due to the size and modulus, and the high shear modulus of matrix, was revealed to predominant strengthening mechanism, accounting for over 50 % of the yield strength of the AlxCrNbVMo RHEAs.