Thermal activation processes of tensile deformation in γ-TiAl alloy

Thermal activation parameters: activation volume V, activation enthalpy ΔH, activation free enthalpy ΔG and activation entropy ΔS of tensile deformation at yield point of a near-lamellar γ-titanium aluminide of Ti–47a/oAl–2a/oMn–2a/oNb–0.8v/oTiB2 have been measured in a wide temperature range from 77 to 1273 K. From the values and their temperature dependence of the measured activation parameters, as well as the temperature dependence of the yield stress, the dislocation mechanisms of tensile deformation of γ-titanium aluminide have been speculated. It is found that there exist three temperature regions, which correspond to different possible thermal activation mechanisms of dislocation motion. In low temperature region (77–398 K), the mechanism is mainly characterized by the overcoming of Peierls–Nabarro friction. In intermediate temperature region (523–973 K), the mechanism is a weak thermal activated process although the plastic flow stress is neither sensitive to temperature nor to the strain rate. In the high temperature region (973–1273 K), the rate controlling mechanism is dislocation climbing. In addition, it is found that, activation entropy ΔS, whose variation with temperature is similar to that of activation volume V, also reflects the thermal activation mechanism of dislocation movement in some degree.