On the influence of thermomechanical processing on the fracture behavior of gamma-based titanium aluminides. II. Effects of alloying with Cr and Nb

The effects of microstructure on the tensile and fracture behavior of Ti-48Al-1.5Cr and Ti-48Al-2Cr-2Nb (compositions stated in atomic % unless stated otherwise) are investigated. Microstructures with different equiaxed/lamellar grain size and volume fractions are produced by extrusion with reduction ratios of 10:1 and 14:1, prior to annealing in the α + γ and/or α₂ + γ phase fields. Room-and elevated-temperature tensile ductility, yield strength and ultimate tensile strength are shown to exhibit an inverse square root dependence on the average equiaxed/lamellar grain size in Ti-48Al-1.5Cr extruded with a 14:1 reduction ratio. A similar Hall-Petch dependence of room-temperature fracture toughness on the average equiaxed/lamellar grain size is also demonstrated in the Ti-48Al-1.5 Cr alloy extruded with a reduction ratio of 14:1. The latter is also shown to have better fracture properties than Ti-48Al-2Cr-2Nb and Ti-48Al-1.5Cr extruded with a reduction ratio of 10:1. The implications of the results are discussed for potential structural applications.