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Abstract
By means of heat treatment, creep properties measurement and microstructure observation, we investigated the influence of heat treatment on microstructure and creep properties of TiAl–Nb alloy. Results showed that the microstructure of as-cast TiAl–Nb alloy consists of γ/α phases with a lamellar structure. Boundaries with irregular jagged shapes are located between the different oriented lamellar γ/α phases. After solution and aging treatment, uniform and regular lamellar γ/α phases in the TiAl–Nb alloy were obtained, and the boundaries between the lamellar groups with different orientations displayed regular and straight features. The creep lifetime of as cast TiAl–Nb alloy at 200 MPa/800°C was measured to be 147 h, and the one of the alloys after being heat treated was enhanced to 297 h. The creep activation energy of the heat treated alloy was measured to be Q = 366 kJ mol−1 in the ranges of the applied temperatures and stresses. During creep, the cracks in the alloy are firstly initiated and propagated along the boundaries parallel to the lamellar γ/α phases along the direction of about a 45° angle relative to the stress axis, which is thought to be the fracture mechanism of the alloy during creep.
Acknowledgement
We are grateful for financial support from the National basic Research Program of China (no. 2011CB605506).