Effect of composition and cooling rate on the transformation of α to γ phase in TiAl alloys

Microstructure controls mechanical properties of TiAl-based alloys and it does so in three ways: alloy composition, thermomechanical (dynamic), and static heat treatments. This study considers the effect of composition and cooling rate in the transformation temperature from hcp-α phase to fct-γ phase in the α and γ phase field. The data for three Ti–46Al–4–8Nb alloys show that α and γ transformation temperature varies by 70 °C by changing the cooling rate over a factor of 40. Compared to the effects of cooling rate, the effect of composition on the α–γ transformation is minimal. Microstructural examination following a change in cooling rate from the post-extrusion heat treatment reveals differences in the desired lamellar structure and suggests the alloy composition and heat treatment cooling rate for optimal properties.