Development of α precipitates in metastable Ti-5Al-5Mo-5V-3Cr and similar alloys

Present work describes the development of the α phase in β WQ specimens of Ti-5Al-5Mo-5V-3Cr (A1), Ti-5Al-3.5Mo-7.2V-3Cr (A2), Ti-5Al-5Mo-8.6V-1.5Cr (A3) and Ti-5Al-3.5Mo-5V-3.94Cr (A4) alloys as function of different ageing temperatures and time intervals. The α phase formed during ageing display different morphologies namely, thin film on prior β grain boundaries, sub boundary and islands of the α phase within the β matrix. Mechanism of the formation of these morphologies has been explained. The fine and even distribution of the α phase in β matrix exhibit two distinct features i.e. uniform distribution of α laths with two variants and clusters of parallel α laths. The α phase presents in all morphologies is transformed to Widmanstatten type morphology on further increase in ageing temperature and time. The development of the α phase in these alloys at 300 and 400 °C results in significant increase in hardness which is attributed to typical precipitation hardening.