Hot deformation response of titanium aluminides Ti–45Al-(5, 10)Nb-0.2B-0.2C with pre-conditioned microstructures

Abstract

Two titanium aluminide (TiAl) based compositions with different niobium (Nb) contents, namely Ti–45Al–5Nb-0.2B-0.2C and Ti–45Al–10Nb-0.2B-0.2C, have been investigated for their hot deformation response. Prior to deformation, microstructural features were modified by a specially designed thermal treatment. The modified microstructures were intended to be equiaxed to facilitate the deformation response. Deformation responses of materials with modified microstructures were examined using isothermal hot compression tests. Strain rate sensitivity maps were generated from the stress-strain curves and suitable domains for optimal processing were identified. The strain rate sensitivity maps show that the workability of the alloys decreases with increasing strain rate and decreasing temperature. An increase in the proportion of dynamically recrystallized grains, which is indicated by deviation from the ideal orientation relationship between the phases, corresponds to the regions of high strain rate sensitivity. The processing domain for the alloy Ti–45Al–5Nb-0.2B-0.2C has been identified within the temperature range 1075 °C–1200 °C at the strain rate 0.1 s−1, whereas for the Ti–45Al–10Nb-0.2B-0.2C alloy, the temperature range of 1125 °C–1200 °C has been found to be most suitable processing domain at the same strain rate.