Tensile creep behavior of a heat treated β-solidified γ-TiAl alloy: The development of dynamic recrystallization and the role of B2 phase

Abstract

The tensile creep behavior of a heat treated β-solidified γ-TiAl alloy has been investigated at 800 °C under 250–300 MPa. Results indicate that the heat treatment procedure proposed in this study can improve creep resistance of the alloy. Combined with kinetic analysis (stress exponent n = 3.36) and TEM observation, it can be inferred that creep deformation is dominated by viscous dislocation glide, and assisted by mechanical twinning. It is found that both twin boundary and TiB can hinder dislocation movement and strengthen creep resistance. During creep, there are obvious dynamic recrystallization (DRX) and B2 phase precipitation. On the one hand, DRX volume fraction increases with the increase of creep stress or the extension of creep time. Meanwhile, TiB can act as nucleation sites of recrystallized γ grains. On the other hand, there are two kinds of B2 phase precipitation behaviors: (ⅰ) thin B2 laths are formed in α2 lamellae; (ⅱ) blocky B2 phases are formed at colony boundary. Creep deformation is mainly completed by γ phase, B2 phase can involve in the deformation only under specific creep conditions. Due to poor deformation ability of B2 phase, creep voids prefer to nucleate at the γ-B2 interface and B2-colony interface. When voids are connected, cracks are formed and begin to propagate, eventually leading to creep failure in brittle-ductile mixed fracture.