Effects of Cr addition and heat treatment on the microstructure and tensile properties of a cast Ti45Al3Cr (at.%) alloy

The microstructure and tensile properties of a cast Ti45Al3Cr (at.%) alloy have been investigated based on comparison with a cast Ti-45Al (at.%) binary alloy. It was found that the addition of Cr causes the formation of dispersed β2 particles, an increase in the volume fraction and lamellar width of the γ phase, and degeneration of α2 plates. Annealing in the (α2 + γ) two-phase region has little effect on the fully lamellar cast microstructure. However, heat treatment in the (α2 + γ) two-phase region results in significant continuous and discontinuous coarsening. The addition of Cr improves the tensile ductility but lowers the yield strength. The former effect may be attributed to the more uniform plastic deformation in the Cr-modified lamellar microstructure, and the latter could be caused by the thickening of γ lamellae. The discontinuous coarsening reduces the lamellar colony size in the binary alloy and produces fine-grained blocky phases in the ternary alloy, leading to higher yield and fracture strengths.