Effect of V on the deformation mechanisms and mechanical properties of Ti-5Mo-4Cr-xV-1Zr metastable β titanium alloys

Abstract

To overcome the trade-off between strength and ductility in structural titanium alloys, various novel transformation-induced plasticity (TRIP) and/or twinning-induced plasticity (TWIP) metastable β titanium alloys have been developed in recent years. Based on the design of the d-electron theory, average electron-to-atom ratio ($\overline{e/\alpha }$) and atomic radius difference ($\overline{\Delta r}$) theory, the stability of β phase was regulated by fine-tuning the content of V element in Ti-5Mo-4Cr-xV-1Zr (x = 0, 1, 2, 3 wt.%, named T0V, T1V, T2V, T3V) alloys, aiming to reveal the influence of V content on the alloy's microstructure, mechanical properties and deformation mechanisms. The experimental results show that with the increase of V content, the β phase grain size decreases gradually, and its stability is significantly enhanced, inhibiting the formation and growth of the athermal ω (ω_ath) phase. Additionally, the T (0–3)V alloys exhibit similar TD//<101> texture. Stress-induced martensitic α″ transformation (SIM α″) and {332}<113> deformation twinning exist in the T (0–3)V alloys during tensile deformation. Moreover, with increasing V content, the dominant deformation mechanisms shifts from the TRIP effect (T0V alloy) to the combined TWIP-TRIP effect (T1V alloy), and finally to the TWIP effect (T2V and T3V alloys). Mechanical testing results show that with increasing V content, the total elongation after fracture gradually decreases, while the yield strength, tensile strength, toughness, and strain hardening rate (SHR) initially increase and then decrease. The T1V alloy exhibits the best comprehensive properties, including a yield strength of ∼689 MPa, tensile strength of ∼935 MPa, total elongation after fracture of ∼39 %, and toughness of ∼333.0 MJ/m³. Furthermore, the synergistic effect of TWIP and TRIP in the T1V alloy significantly enhances its SHR, which is superior to the SHR of T0V and T3V alloys, i.e., T1V_TWIP-TRIP (SHR: 2771 MPa) > T0V_TRIP (SHR: 2415 MPa) > T3V_TWIP (SHR: 2119 MPa).