Stress and temperature dependence of creep rate in γ-TiAl single phase alloy

The creep deformation of gamma-TiAl single phase alloys with ordered L1(O) structure has been characterized in terms of the activation energy for creep Q(c),, stress exponent n and internal stress sigma(i). The stress exponent of the minimum creep rates n becomes 3 at stresses below 70 MPa, regardless of the temperatures from 1123 to 1223 K, whereas it increases to 8 above 150 MPa. The activation energy for creep Q(c) obtained at 68.6 MPa varies from 300 to 700 kJ/mol with increasing the temperature. The large variation of Q(c) is attributed to the temperature dependence of dislocation substructure. The internal stress sigma(i) is measured by strain dip tests decreases with increasing the temperature. Based on these findings, it is found that the activation energy Q(c)* obtained at a constant effective stress sigma(c) (=sigma(a)-sigma(i)) becomes 245 kJ/mol, independent of the temperature.