Thermo-kinetic model of creep controlled by thermally activated detachment of dislocations from nano-oxides revisited

Coarse-grained ferritic oxide dispersion strengthened (ODS) alloys represent the top creep and oxidation-resistant materials for applications at 1000–1300 °C. The long-term shape stability of loaded parts is conditioned by extremely low creep rates achieved by the sticking of dislocations at the back side of nano-oxides. At such temperatures, however, the detachment of dislocations from the nano-oxides can take place by thermal activation. The existing models of this phenomenon assume that dislocations move by slip and only oxides have to be overcome by a combination of slip and climb. Thus, such models are applicable for temperatures significantly below 1000 °C. To fill this gap, we have developed a new model applicable to temperatures over 1000 °C, where dislocation climb in the matrix is also considered. The simulations based on the model indicate that the energy barrier for dislocation detachment is up to five times higher than that according to the state-of-the-art models. The creep strength benefits from an increased volume fraction and optimal size of nano-oxides of about 20 nm and increased dislocation line-energy reduction at the particle/matrix interface. The present model thus provides recommendations, how the ODS alloys with the best long-term creep resistance should be designed.