Nature of phase transformations in metastable β-Ti alloy: An in situ study on Ti–5Al–5Mo–5V–3Cr alloy

Metastable β-Ti alloys are important alloys for the aerospace industry. Understanding the often complex microstructure evolution in these alloys is essential to control their mechanical properties. Hence, we conducted heat treatment experiments combined with in situ electrical resistance measurements to investigate the phase transformation behaviour of a metastable β-Ti alloy, Ti–5Al–5Mo–5V–3Cr (Ti-5553). The results were condensed into a Time-Temperature-Transformation diagram, which revealed three distinct phase transformation regions: ω-phase region, α-phase region, and the likely presence of an α₂-phase region. The phase field ‘nose’ for α-phase formation lies at ∼600 °C. Additionally, the results showed that the transition between pseudo-spinodal and isothermal ω-phase-assisted mechanisms for α-phase formation occurs at a heating rate of ∼30 °C/min.