Fracture Toughness and High Temperature Strength of Cast and HIP’ed Zr Added TiAl

We reported before that cast and HIP’ed TiAl alloys with adequate Zr-addition showed the excellent strength-ductility balance at room temperature. In this study, the tensile strength at high temperatures and the fracture toughness at room temperature of the Zr-added alloys were investigated. Ti-48 at%Al alloy was chosen as the base alloy and Zr was added up to 4 at% in the base alloy with Al/(Ti+Al) of 0.48 atomic ratio. Microstructure of Zr-added alloys consisted of higher volume fraction of the grains in lamellar form and equiaxed γ grains. Equiaxed γ region had the Zr segregated zone which enclosed the lamellar colonies forming like a network. This microstructural feature resulted in the excellent strength-ductility balance at room temperature as discussed in detail previously. In the results of tensile test at high temperatures up to 1073 K, 2 at%Zr-added alloy showed higher strength than that of the base alloy. Fracture toughness at room temperature increased with increasing Zr content. For the binary alloy and the Zr-added alloys, the tensile strength at 1073 K and the fracture toughness at room temperature showed a linear relationship with the volume fraction of the grains in lamellar form. Therefore the advantages of the lamellar structure brought about the higher tensile strength at high temperatures and fracture toughness in Zr-added alloys. 2 at%Zr-added alloy is superior to the base alloy and also well balanced compare with the other binary alloys in the various properties, strength at RT and high temperature, ductility at RT and fracture toughness.