Effect of variation in Zr content on microstructure and high-temperature tensile properties of a γ-TiAl alloy

A series of Ti-46Al-xZr (x = 0, 1, 2, 3, 4, 5 at.%) alloys were prepared to systematically investigate the effect of variation in Zr content on the microstructure and high-temperature tensile properties. The results show that the addition of Zr intensifies the solidification segregation and promotes the formation of blocky γ phase in TiAl alloys. With the increase in Zr content from 1 to 5 at.%, the volume fraction of the blocky γ phase increases from 0.2 to 12.8 %, and the solidification microstructure is transformed from a fully lamellar to a nearly lamellar microstructure composed of the blocky γ phase and lamellar colonies. Because Zr stabilises the γ phase, continuous and discontinuous coarsening occur simultaneously; the former is observed inside the colony, whereas the latter occurs between two adjacent lamellar colonies. The high-temperature tensile results show that the ultimate tensile strength at 800 °C of the Ti-46Al-4Zr alloy (692 MPa) is significantly greater than that of the Ti-46Al alloy (351 MPa), which is attributed to solid solution strengthening and the coordinated deformation of blocky γ phase.