Analysis of thermal and athermal deformation mechanisms during creep of γ-TiAl alloys

The creep deformation of a near-γ titanium aluminide alloy with equiaxed and lamellar structures has been studied to understand its behaviour as a function of microstructural evolution during the early stages of creep. The lamellar alloy exhibits more pronounced hardening during the primary stage of creep leading to a much better creep resistance and a minimum creep rate two orders of magnitude lower than that of the equiaxed alloy. Transmission electron microscopy observations have confirmed that the active deformation mechanisms are the same for both microstructural states, namely extensive slip of single 1/2〈110〉 dislocations and mechanical twinning. Using the values of apparent activation energies and activation volumes measured for both microstructural states, it has been possible to describe the better creep resistance of the lamellar alloy to the presence of a higher density of interfaces at which dislocations remain immobile.