Creep characteristics and internal stress in γ-TiAl

The creep deformation of γ-TiAl single phase alloy with ordered L10 structure has been characterized in terms of activation energy for creep Qc, stress exponent n and internal stress σi. The stress exponent of minimum creep rate n becomes 3 at stresses below 70 MPa in the temperatures between 1123 and 1223 K, whereas it increases to 8 above 150 MPa. The activation energy for creep Qc obtained at 68.6 MPa increases from 250 to 700 kJ mol−1 with increasing the temperature. The large variation of Qc is attributed to the temperature dependence of dislocation substructure. The internal stress σi measured by strain dip tests decreases with increasing temperature. Based on these findings, it is found that the activation energy Q*c obtained at a constant effective stress σe (=σa−σi) becomes 245 kJ mol−1, independent of the temperature.