Microstructure and tensile properties of as-cast Ti-45Al-(8-9)Nb-(W, B, Y) alloy

Microstructure and tensile properties of high Nb containing TiAl alloy, with nominal composition of Ti-45Al-(8-9)Nb-(W, B, Y) (at.%), were investigated. The results showed that the as-cast alloy had near lamellar microstructure composed of fine homogenous lamellar colonies, with a size of about 70 μm, and a small amount of β phase and equiaxed γ phase. The β phase existed either on the boundaries of the lamellar colonies in irregular morphology or in the lamellar colonies in lamellar or blocky morphology. Equiaxed γ phase existed on the boundaries of lamellar colonies. There also existed some borides in three morphologies: convoluted flakes, ribbons and particles. The alloy had mediate tensile properties at both room temperature (RT) and high temperature. At RT, ultimate tensile strength level of 668 MPa and 0.49% plastic elongation were obtained, and the brittle-to-ductile transition temperature was higher than 815 °C. Cracks propagated in transgranular mode predominantly, and borides and β phase were detrimental to the ductility of the as-cast alloy.