Microstructures and Creep Behavior of As-Cast TiAl-Nb Alloy

By means of creep properties measurement and microstructure observation, an investigation was carried out to study the creep behaviors of the as-cast TiAl-Nb alloy at temperature near 910 oC. Results showed that the microstructure of as-cast TiAl-Nb alloy consisted of γ/α2 phases with the lamellar feature, and the boundaries with irregular serrated configuration consisted of single γ phase, and located in between the lamellar γ/α2 phases with different orientations. The as-cast TiAl-Nb alloy displayed a better creep resistance at high temperature and longer creep life. Compared to α2 -Ti3Al phase, the γ phase possessed a weaker strength, therefore, the crack was easily initiated along the boundaries at about 45° angles relative to the stress axis, and propagated along the boundaries parallel to the orientation of lamellar γ/α2 phases up to the occurrence of creep fracture. Thereinto, the tearing edges formed on the surface of the fracture being inclined with the lamellar γ/α2 phases are attributed to the α2-Ti3Al phase with better strength hindering the crack propagation during creep.