Analysis of the minimum creep rates of TiAl alloys

The creep rate limiting factors for secondary creep of TiAl alloys has been analyzed based on the experimental data from 40 previous studies. The experimental data can be well predicted using a dislocation glide (DG) equation ε̇min(DG)=K0 exp(−QL/RT) sinh(σ/σ0) or a grain boundary (GB) sliding equation ε̇min(GB)=Dgb0 exp(−Qgb/RT)d−2σ−2 with the activation energies QL and Qgb to be of 375 and 218 kJ/mol, respectively. The material constants K0 and Dgb0 were determined for TiAl alloys with various microstructures and compositions. For duplex (DP) and near-gamma (NG) TiAl alloys, grain size (d) is the major rate limiting factor and the constant K0 is proportional to the d−1.5. In fully-lamellar (FL) TiAl alloys, reducing lamellar spacing increases the stress constant σ0. Additions of W, C, N, or Si improve the creep resistance of TiAl by decreasing the constants K0 and Dgb0 and increasing the constant σ0. The resultant equations accurately predict the minimum creep rates of various TiAl alloys in a broad temperature range of 600–900 °C.