Effect of Al addition on the microstructure, mechanical and wear properties of TiZrNbHf refractory high entropy alloys

A series of Al_xTiZrNbHf refractory high entropy alloys (RHEAs) were prepared to investigate the mechanical and wear properties. Despite the different crystal structures of each constituent, the RHEAs exhibited body centered cubic (BCC) phase structures as revealed by X-ray diffraction and transmission electron microscopy. Along with the primary BCC phase, another ordered BCC phase appeared in AlTiZrNbHf, being supported by a high negative mixing enthalpy (<−16.28 kJ-mol⁻¹) and a low valence electron concentration (< 4.04). The improved mechanical properties and wear resistance by the Al addition are ascribed to severe lattice distortion and second phase strengthening. These findings highlight significant alterations in the microstructure, mechanical and wear properties with the Al addition, which are beneficial to the design of alloys for wear applications.