Simultaneously enhanced strength and ductility in a metastable β-Ti alloy by stress-induced hierarchical twin structure

A novel metastable β-Ti alloy Ti-4Mo-3Cr-1Fe with high strength and high ductility was developed through controlling the alloyʼs stability and deformation mechanisms. The microstructure consists of randomly oriented β-grains containing an even distribution of athermal ω precipitates. Under tensile loading, the alloy exhibits unprecedented and comprehensive mechanical properties including a high yield strength of 870 MPa, excellent total elongation of 41% and an ultrahigh strain hardening rate of 2.5 GPa. Based on investigations of deformation microstructures, the superior mechanical properties are attributed to stress-induced formation of a complex nano-scale hierarchical twin structure which is promoted by reversion of ω precipitates.