Mechanisms that are associated with acceleration of the creep rate in the tertiary stage such as microstructure degradation, cavitation, necking instability and recovery have been known for a long time. Numerous empirical models for tertiary creep exist in the literature, not least to describe the development of creep damage, which is vital for understanding creep rupture. Unfortunately, these models almost invariably involve parameters that are not accurately known and have to be fitted to experimental data. Basic models that take all the relevant mechanisms into account which makes them predictive have been missing. Only recently, quantitative basic models have been developed for the recovery of the dislocation structure during tertiary creep and for the formation and growth of creep cavities. These models are employed in the present paper to compute the creep strain versus time curves for copper including tertiary creep without the use of any adjustable parameters. A satisfactory representation of observed tertiary creep has been achieved. In addition, the role of necking is analysed with both uniaxial and multiaxial methods.

In spite of its huge technical significance, there does not seem to be consensus about how to model the precipitation contribution to the creep strength. Most contributions in the literature are based on a constant internal stress (also called back stress or threshold stress) from the precipitation. It is well-known and it will also be demonstrated in the paper that this assumption is at variance with observations except for some ODS alloys. There is, however, one model developed by Eliasson et al. (Key Eng Mater 171-174:277-284, 2000) that seems to be able to represent experimental data without the use of any adjustable parameters. It has successfully been applied to describe the creep strength of austenitic stainless steels. Due to the fact that various mechanisms contribute to the creep strength in these steels, the model has not been fully verified. The purpose of this paper is to apply the model to published creep data for Cu-Co alloys, where the precipitation totally dominates the strength contribution to validate the model. In the paper, it is demonstrated that the model can indeed describe the influence of applied stress, alloy composition and heat treatment for the three analysed Cu-Co alloys.

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