Creep behavior and fracture mechanism of high Al/Nb-containing TiAl alloy

High Al content inhibits the formation of B2 phase, which improves creep resistance in high Al/Nb-containing TiAl alloys. In this work, the microstructure evolution and creep behavior of TiAl based alloy Ti-46Al-8Nb (at.%) with a high Al/Nb content, produced by the vacuum consumable electrode melting technology and the electromagnetic cold crucible melting technology, were studied. The microstructure of the Ti-46Al-8Nb alloy is composed of α 2 /γ phases arranged in layers with different orientations, which possesses smooth grain boundaries due to small-blocky segregation and irregular serrated grain boundaries caused by large-blocky segregation. Under conditions of 780–820 °C and 125–175 MPa for 200 h, it exhibits typical power-law creep characteristics. The apparent activation energy of creep ( Q ) and apparent stress exponent ( n ) of the Ti-46Al-8Nb alloy are Q =274 kJ·mol −1 and n =1.97, respectively. The creep deformation mechanism is grain boundary sliding. Cracks easily form at the smooth boundary. The irregular serrated boundaries with small specific surface area hinder the dislocation movement, thereby improving the boundary creep resistance. When the stress concentration reaches a certain degree, the cracks will initiate between the lamellar structures within the grain. The crack usually propagates along the boundary perpendicular to or at an angle of 45° with the stress axis until creep failure occurs.