Deformation Mechanism Of New TRIP/TWIP Ti-Mo-Zr Alloys With High Strength And Ductility

Titanium alloys are widely used in aerospace,biomedical field,and chemical industries due to their low density,high specific strength,excellent corrosion resistance,and good biocompatibility.However,compared with stainless steel and CoCr alloys,traditional titanium alloys used in construction exhibit two significant disadvantages: low plasticity and poor work hardening ability.These limitations limit the application and development of titanium alloys under the conditions of high strength and high plasticity.In view of the above problems,the TRIP/TWIP effect in stainless steel(TRIP: Transformation induced plasticity;TWIP: Twinning induced plasticity)was introduced into the design of titanium alloy.Based on the research of Ti-12 Mo alloy,using the d-electron design method and controlling the electron concentration of the alloy,we designed a new β Ti-Mo-based titanium alloy structural material with TRIP/TWIP effect by controlling the β stability of the alloy,to make the alloy exhibit high strength,high plasticity and good work hardening behavior.We characterized the mechanical properties,microstructure evolution and deformation mechanism of Ti-Mo based alloys with the TRIP/TWIP effect by means of Instron universal tensile testing machine,optical microscopy(OM),X-ray diffractometry(XRD),electron backscatter diffraction(EBSD)and transmission electron microscopy(TEM).The experimental results show that the designed Ti-12Mo-Zr alloy has excellent comprehensive properties.The Ti-12Mo-5Zr alloy has a yield strength of about 640 MPa,a tensile strength(UTS)of about 1.0 GPa,and a uniform plastic strain ε ≈ 0.35.Ti-12Mo-15 Zr has a yield strength of about 800 MPa,a tensile strength of about 1.1 GPa,and uniform plasticity,and a uniform plastic strain ε ≈ 0.18.The addition of Zr enhances the strength of the alloy by means of solid solution strengthening.On the other hand,the β-stability of the alloy(including the effect of Mo)is increased with the increase of Zr content,and the stress-induced martensitic transformation is inhibited.That make the deformation mode of Ti-12Mo-5Zr(TRIP + TWIP + Slip)transform to the deformation mode(TWIP + slip)of Ti-12Mo-15 Zr.