Fundamental models and testing of creep in copper

Many sustainable technologies for energy production, for example, generation IV nuclear system, demand the use of materials operating at elevated temperatures for long duration of up to 60 years. Requirements that are even more stringent are found for creep exposed copper canisters for disposal of spent nuclear waste. The canisters should stay intact for thousands of years. Traditional design procedures that involve empirical extrapolation of creep data are no longer reliable for such extended times. Instead physically based material models have to be used. The final stage of creep before rupture, tertiary creep has been handled with empirical methods with adjustable parameters in the past, which makes it difficult to safely identify the controlling mechanisms. A physically based model has been developed for copper taking the substructure, cavitation and necking into account. To improve the understanding of the important contribution from particles to the creep strength an earlier formulated model has analyzed and further developed. The model has successfully been able to describe the temperature and stress dependence of precipitation hardening for copper-cobalt alloys, where this contribution totally dominates the creep strength. Multiaxial stress states are crucial for practically all high temperature applications. Fundamental material models have been extended for such conditions. These models have been compared with strain and stress controlled tests for notched specimens that have been performed.