Composition design of a novel Ti-6Mo-3.5Cr-1Zr alloy with high-strength and ultrahigh-ductility

The strength-elongation to fracture(εf)trade-off and low strain hardening rate have been a longstanding dilemma in titanium alloys.In this work,we innovatively manufactured a novel Ti-6Mo-3.5Cr-1Zr alloy via the introduction of a stress-induced strengthening phase into the material.Stress-inducedω(SIω)phase transformation was expected to replace theα''martensitic transformation that resulted in the low yield strength of titanium alloys.The obtained alloy exhibited an extremely high strain hardening rate of up to^1820 MPa.The true peak tensile strength andεfreached^1242 MPa and^40%,respectively.The intrinsic mechanisms underlying the simultaneous improvement of strength and ductility of the material were systematically investigated via in-situ and ex-situ characterizations.In-situ electron backscatter diffraction(EBSD)/digital image correlation(DIC)results showed that SIωphase transformation dominated the early stage of plastic deformation(1.5%–3%)and promoted the strain partitioning between the stress-induced bands andβmatrix.Subsequently,the formation of{332}<113>βtwins andωtwins was observed via ex-situ EBSD.In-situ transmission electron microscopy results revealed that dislocation pile-up(DPU)occurred at the SIω/βinterface.The coupling effects associated with the transformation induced plasticity(TRIP),twinning induced plasticity(TWIP),and DPU mechanisms contributed to the enhanced strength andεfof the designed titanium alloy.