Thermal activation volume V, activation enthalpy △H, activation free enthalpy △G and activation entropy △S of tensile deformation
of a
gamma titanium aluminide have been measured in a temperature range from low temperature(285 K) to 1273 K. The γ-TiAl has a chemical composition of Ti-47Al-2Mn-2Nb-0.8TiB2 and a microstructure of near lamellar, and the measurement was conducted at yield points. From the values and their temperature dependence of the measured activation parameters, as well as the temperature dependence of yield stress,the dislocation mechanisms of tensile deformation of the alloy 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(285-398K), the mechanism is mainly characterized by the overcoming of Peierls-Nabarro resistence. In intermediate temperature region(523-873K), the mechanism is a weak thermally activated process as the plastic flow is neither sensitive to temperature nor to the strain rate.In high temperature region(≥973 K), the rate controlling machanism is dislocation climbing.In addition,it is found that,activation entropy △S, whose variation with temperature is similar to that of activation volume V, also reflects the thermal activation mechanism of dislocation movement in some degree.