Ductile Ti-rich high-entropy alloy controlled by stress induced martensitic transformation and mechanical twinning

Body centered cubic type of refractory high-entropy alloys (HEAs) have high strength at room and elevated temperatures, but suffer from the strength-ductility trade-off dilemma, making their application for structural materials severely impeded. In this article, we report a strategy to break this puzzle by introducing successive stress-induced martensitic transformation (SIMT) and mechanical twinning in Ti-rich refractory TiZrHfAlNb HEA via controlling the grain size. The HEA exhibits superior ductility featured by fracture and uniform elongation as high as 40% and 33%, respectively, at ambient temperature. The plasticizing and toughening mechanisms for the HEA with different grain sizes can be described as following: in the HEA with small grains, the SIMT takes place followed by the martensite variants reorientation; in that with coarse grains, mechanical twinning of α″ phase comes up with the preferential orientation relationship of [111]β//[101]α″_M//[-10-1]α″_T after the SIMT.