A novel quaternary equiatomic Ti-Zr-Nb-Ta medium entropy alloy (MEA)

The high strength and low ductility of body-centred cubic (BCC) high entropy alloys (HEAs) both result from the severe lattice-distortion effect as measured by the atomic mismatch (delta). We report a novel quaternary equiatomic Ti-Zr-Nb-Ta (delta = 4.8%) medium entropy alloy (MEA), redesigned from a quinary equiatomic Ti-Zr-Nb-TaMo (delta = 5.5%) HEA, for much improved strength-ductility combinations and potentially improved biocompatibility by reducing delta through excluding Mo. The as-cast MEA exhibited a single BCC phase and achieved compressive yield strength of 1100 +/- 90 MPa, strain of 48 +/- 6%, which is 4 times higher than that of the Ti-ZrNb-Ta-Mo HEA, and modulus of 116 +/- 6 GPa similar to Ti-6Al-4V.