Physical interpretation of a viscoplastic model applied to high temperature performance of a nickel-base superalloy

In the precipitation-hardened superalloy IN 738 LC several deformation mechanisms, i.e. cutting of the γ' phase or climb-assisted bypassing of precipitates by dislocations as well as the formation of dislocation networks at the γ-γ' interfaces and particle coarsening, were observed depending on temperature and strain rate. For the description of the material behaviour a viscoplastic model based on the concept of internal stress is used. The internal stresses are attributed to particle strengthening and accumulation of dislocations. The used constitutive model is able to describe viscoplastic behaviour like the strain rate dependence and an increasing creep rate at small inelastic strain, i.e. the absence of a classical stationary creep range. Different hardening and softening rates of the model are active in different loading ranges. This can be explained by the operation ranges of different micromechanisms. (orig.)