The ω phase transformation during the low temperature aging and low rate heating process of metastable β titanium alloys

The ω phase transformation during isothermal aging and continuous heating process for three metastable β titanium alloys, Ti-5Al-5Mo-5V-3Cr (Ti-5553), Ti-5Al-5Mo-5V-3Cr-1Zr (Ti-55531) and Ti-7Mo-3Cr-3Nb-3Al (Ti-7333) were studied by dilatometry and transmission electron microscopy (TEM) methods. Results show that the ω phase transformation window of Ti-5553 and Ti-55531 alloys is about 275 °C–350 °C, while that of Ti-7333 alloy is 200 °C–375 °C. The ω particles produced during ageing process is larger than that produced during continuous heating process. A new developed Mo equivalent formula was used to discuss the effect of chemical composition on ω phase transformation for metastable β titanium alloys. It was found that metastable β titanium alloys with lower Mo equivalent have lower starting temperature of ω phase transformation and wider transformation window.