Abstract
The creep data for copper strenghtened with fine alumina particles - a commercial GlidCop Al-15 alloy, presented by Broyles et al. - are interpreted in terms of the true threshold stress. It is shown that at high testing temperatures 973 and 998 K the minimum creep strain rate is apparently controlled by lattice self-diffusion in the alloy matrix - copper - and that the true stress exponent of minimum creep strain rate is very close to that reported for copper, i. e. close to 5. At much lower testing temperatures of 748 and 773 K, the minimum creep strain rate is found to be controlled by the dislocation core diffusion in copper, and, accordingly, the true stress exponent of minimum creep strain rate is close to 7. The creep data available for these two temperatures made it possible to prove that the apparent activation energy of creep is much higher than the activation enthalpy of dislocation core diffusion, which is essentially due to the temperature dependence of the true threshold stress; the contribution of the temperature dependence of the shear modulus of copper is not significant. Independently of the testing temperatures under consideration, the origin of the true threshold stress is discussed in relation to the detachment stress characterizing the strength of attractive dislocation/particle interaction - the stress necessary to athermally detach a dislocation from an incoherent interacting particle. It is suggested that the measured true threshold stress can be identified with the above-defined detachment stress only if the relaxation factor appearing in the expression for the detachment stress increases with increasing temperature.

Key words
copper alloy, powder processing, high temperature, creep, threshold stress

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