Creep in copper dispersion strengthened with alumina particles (ODS copper)

The creep behaviour of ODS copper is investigated in two distinctly different temperature intervals. In both intervals creep exhibits threshold behaviour; the true threshold stress decreases with increasing temperature. In the lower temperature interval (673–773 K) the creep strain rate is dislocation core diffusion controlled and the true stress exponent is close to 7. In the higher temperature interval (923–1023 K) creep is controlled by the lattice self-diffusion and the true stress exponent is close to 5. In both temperature intervals the apparent activation energies are much higher than the respective activation enthalpies of diffusion, i.e. the true activation energies of creep, and the apparent stress exponents are much higher than the respective true stress exponents. The differences of apparent and true activation energies are fully explained by the observed temperature dependences of the true threshold stresses. The differences between the apparent and the true stress exponents are shown to be inherent to the true threshold creep behaviour.