Phase evolution and mechanical properties of AlxCrTaTi refractory medium entropy alloys

In multi-principal refractory alloys (high-entropy alloys, medium-entropy alloys), the presence of the second phase has an important influence on the mechanical properties of the alloys. In this paper, AlxCrTaTi (x = 0, 0.25, 0.5, 1.0) refractory medium-entropy alloys were prepared by vacuum arc melting method, and the microstructure, density, and mechanical properties were investigated. The CrTaTi alloy consists of BCC dendritic and C15 Laves phases, whereas the AlxCrTaTi alloys consist of a two-phase eutectic organization (BCC phase and C14 Laves phase). With the increase of Al content, the content of the second phase increases from 15.97 % to 42.19 %, resulting in an increase in the yield strength of the alloy from 1491 MPa to 2354 MPa at 25 °C, and from 253 MPa to 426 MPa at 1000 °C. The addition of Al element changes the enthalpy, elemental distribution, and solidification process of the alloy, resulting in the formation of Cr-rich and Ti-rich two-phase eutectic organizations in the alloy. With the increase of Al, the second phase strengthening is the main reason for the enhancement of alloy properties. •The study investigated AlxCrTaTi (x = 0,0.25,0.50,1.0 at.%) RMEAs prepared by vacuum arc melting.•The addition of Al can obtain a two-phase eutectic organization and transform the second phase from C15 to C14.•The second phase strengthening is the main strengthening mechanism of alloys.