Microstructures and tensile properties of massively transformed and aged Ti46Al8Nb and Ti46Al8Ta alloys

Fully massively transformed samples of Ti46Al8Nb and Ti46Al8Ta have been HIPped (hot isostatically pressed) in the (α + γ) phase field in order to generate a fine convoluted microstructure and their tensile properties compared with those of samples with coarse lamellar microstructure. It has been found that the yield strengths and ductilities of the microstructurally refined samples were significantly improved with respect to those with coarse microstructures. The proof stresses of the microstructurally refined samples of the Ta- and Nb-containing alloys were almost identical (550 MPa) but the ductility in the Ta-containing alloy is about double that of the Nb-containing alloy, reaching values of up to 1.1% plastic strain. However, there is significant scatter in the elongation in both alloys, which in the case of the Ta-containing alloy has been shown to be associated with segregation which hinders the massive transformation and leads to the formation of some large grains. These observations are discussed in terms of the practicality of using massively transformed and heat-treated cast alloys in engineering components and in terms of the factors controlling the tensile behaviour.