Assessment of θ-projection concept and fracture cavitation

The empirical approach to creep, termed θ-projection concept, is applied to the constant-load data of conventionally cast nickel-base superalloy IN-100 at constant temperature (900 °C). The normal creep curves, obtained at various initial stresses (σ_A = 200−400 MPa), could be accurately represented by this concept. The change in creep curve shape with stress from tertiary dominated to primary dominated view is presented by the change in the ratio of primary (ɛ_p) and tertiary strain (ɛ_t) components to rupture strain (ɛ_R). It is predicted that failure in the present creep conditions is dominated by the GB cavitation and the growth of the cavities is controlled by the coupled GB diffusion and power-law creep mechanism. In an attempt to provide a physical significance to θ-parameters, it is found that the internal structural variable theory and continuous GB cavitation account well, with suitable assumptions, for the θ description of primary and tertiary creep curves, respectively.