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

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 Ti 67 Nb 16 Zr 17 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. (Ti 67 Nb 16 Zr 17) 87 Al 13 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. • Addition of a certain amount of Al to some Ti-Nb-Zr base alloy results in single BCC phase with CSRO. • As-cast (Ti 67 Nb 16 Zr 17) 87 Al 13 alloy has very high specific strength and good elongation. • As-cast (Ti 67 Nb 16 Zr 17) 87 Al 13 alloy has superior mechanical property to most existing M/HEAs. • CSRO plays a dominant role in the mechanical behavior of (Ti 67 Nb 16 Zr 17) 87 Al 13 alloy. [ABSTRACT FROM AUTHOR]