Creep behavior of γ-TiAl polysynthetically twinned crystals

Creep behavior of γ-TiAl polysynthetically twinned crystals has been investigated at temperatures between 700 and 800°C. The results show that the creep behavior of the crystals is strongly dependent on the angle φ between the lamellar boundaries and loading axis. The samples with the angle φ=-45 deg. have the lowest creep resistance, while the samples with φ=0 deg., rather than φ=90 deg., show the strongest creep resistance. The stress exponent and creep activation energy for the power law creep vary with the orientations of samples, which indicates that the creep mechanisms of the samples with different angle φ are quite different. The deformation substructure has been examined by transmission electron microscopy, which shows that both gliding, perhaps also climbing, of dislocations and twining contribute to the creep deformation with some particular observations in the samples with φ=90 deg. in which rotation of the γ plates across a true twin boundary was observed, which indicates the deformation mechanism of the samples is different from the samples in other orientations.