Novel BCC Ti-Al-Nb-Zr medium-entropy alloys with ultrahigh specific strength and ductility

Abstract

Body-centered cubic (BCC) medium-entropy alloys (MEAs) are characterized by high strength, low ductility and often high density due to containing much refractory elements. In this paper, a series of BCC Ti-Al-Nb-Zr medium-entropy alloys were constructed by adding different contents of Al to Ti67Nb16Zr17 base alloy composed of α and β phases. It is shown that an enough addition of Al can depress the formation of α phase, resulting in single BCC structure. (Ti67Nb16Zr17)87Al13 alloy has the best comprehensive mechanical property as the strength-ductility trade-off is well overcome. Its specific strength is up to 230 MPa g−1 cm3 and its elongation is also as high as 18.5% in the as-cast state, better than most existing medium- and high-entropy alloy. It is revealed that abundant nanoscale chemical short-range order (CSRO) in the matrix phase plays an important role in the mechanical response of this alloy.