Microstructural modelling of thermally-driven β grain growth, lamellae & martensite in Ti-6Al-4V

The microstructural kinetics of β grain growth in the β field of a Ti-6Al-4V alloy were studied by a series of controlled heat treatments at constant temperature rates. Heat-ing rates of 5 °C/s, 50 °C/s and 500 °C/s were considered, stopping at different peak temperatures. The thickness evolution of martensitic needles and lamellar α laths, formed on cooling, was also investigated, by soaking the material above its β-transus temperature and cooling down at 5 °C/s, 50 °C/s, 100 °C/s and 300 °C/s till ambient temperature. Quantitative microstructural analyses were used to measure the particle dimensions. The β grain growth kinetics were reasonably well described by a modified Avrami equation. The thickness of α lamellae were a function of the cooling rate and the β grain dimension in which they nucleated. The martensite needle thickness was shown to be a function of the cooling rate to which the material was subjected.