On the role of mechanical twinning in creep of a near-γ TiAl-alloy with duplex microstructure

The role of deformation twinning during creep deformation of a duplex TiAl alloy was studied. Microstructural parameters like interface spacing, twin spacing and twin width were determined. Twinning was observed already after low strains of 0.3% in γ-grains as well as in lamellar grains. Twin formation in lamellar grains is not much affected by the creep parameters (stress, temperature, strain) chosen in this study. However, a clear effect was observed for γ-grains, where the interface spacing decreases with increasing strain and stress. Lower temperatures also promote twinning. Mechanical twinning was identified as one element of the creep deformation mechanism and contributes already in the early stages of creep. Twinning is an easy mode of deformation because of the low stacking fault energy in near-γ TiAl alloys. Neither our results nor what has been reported in the literature so far allow to conclude whether deformation twinning is a creep hardening or softening mechanism. Further TEM investigations in combination with high resolution creep testing are required to study this phenomenon.