Influence of Temperature and Strain Rate on Microstructural Evolution During Hot Compression of Ti-45Al-xNb-0.2C-0.2B Titanium Aluminide Alloys

The hot deformation response of third-generation titanium aluminides with compositions Ti-45Al-5Nb-0.2B-0.2C and Ti-45Al-10Nb-0.2B-0.2C (hereafter referred to as Ti-45-5 and Ti-45-10, respectively) has been investigated through isothermal compression tests. The tests have been carried out in the (alpha 2+gamma)\textbackslashphase regions for both alloys. The flow response, kinetics and microstructural evolution during hot deformation have been analysed in detail, and the outcome of the investigation has been used to predict the processing window for the two alloys. The optimum processing domain for the Ti-45-10 alloy is situated 50 degrees C higher than that of the Ti-45-5 alloy. The post-mortem analyses of the microstructures revealed that deformation in the (alpha 2+gamma) phase field leads to dynamic recrystallisation of all the phases resulting in a distribution of very fine grains. Microstructural features of both alloys depict kinking and breaking of the lamellae for the equivalent temperatures. The higher strength of the Ti-45-10 alloy has been attributed to shifting of the order-disorder transition toward the higher temperature side. In the (alpha+gamma) phase increases more for the Ti-45-10 alloy compared with the Ti-45-5 alloy