Promoting multiple deformation mechanisms and accelerating omega phase precipitation in metastable Ti-10Mo alloy via Cu addition

Metastable titanium alloys usually exhibit low yield strength and rapid decline of strain hardening after reaching the peak. In this work, the addition of 3.5 wt% Cu into Ti-10Mo titanium alloy is investigated. The results indicate that Cu addition enhances both strength and ductility. Notably, the Ti-10Mo-3.5Cu alloy maintains a high strain-hardening ability after the peak, even at a large strain of 27 %. The microstructural evolution at interrupted strains shows that the addition of Cu promotes multiple twinning and phase transformation mechanisms, evidenced by the formation of {332} twins, stress-induced ω phase, stress-induced α″ phase, and {112} twins. For the purpose of utilizing isothermal ω phase (ω_iso) to strengthen the alloy, low-temperature aging (150°C to 350°C) is performed, which significantly enhances the strength, but results in sensitivity of ductility reduction to the aging temperature. The experiment-based statistics reveal that the addition of Cu promotes the rapid precipitation of ω_iso phase, facilitating the increase of strength. However, high-resolution TEM shows that the addition of Cu accelerates the collapse of ω_iso phases, resulting in dramatic decrease of ductility at high aging temperatures. This work provides valuable insights into the design of metastable titanium alloys by regulating the deformation mechanisms and optimizing the precipitation of ω_iso phase to achieve high performance.