Impact of vanadium (V) content on in-situ oxidation, high temperature mechanical strength and tribological properties of Al0.5CrFeNiVx high entropy alloys

In this study, four vanadium (V) containing high entropy alloys (HEAs) Al_0.5CrFeNiV_x (x = 0.25, 0.5, 0.75, 1.0) were developed and investigated, in terms of examining the influence of V content on their microstructure, in-situ oxidation behavior, high temperature mechanical strength, and high temperature tribological performances. An increase in the V content causes precipitation of the Laves phase (VAl₂) in the body-centered cubic (BCC) matrix. This structural transition increases the alloy hardness and compressive strength through solid solution strengthening, precipitation strengthening and grain refinement strengthening. When x is increased from 0.25 to 1, the maximum compressive strength increases from about 2476 to 3241 MPa at room temperature and from about 521 to 797 MPa at 700 °C, respectively. In-situ oxidation investigation reveals that a higher V content accelerates the oxidation and provides a direct evidence of vanadium oxides melting at 700 °C and thus forming the liquid oxide phases on the surface of HEAs. During high temperature tribological contact, the liquid oxide phases minimize the friction, allowing thicker and more complex oxide layers to form on the worn surface to improve the HEAs’ wear resistance. The findings in this work contribute to the development of novel HEAs with superior properties for potential applications that need outstanding mechanical strength, wear resistance, and thermal stability.