Rate dependent ductility and damage threshold: Application to Nickel-based single crystal CMSX-4

A phenomenological damage model is proposed to account for the strain rate dependency of the damaging processes at high temperature. Mechanical softening during tertiary creep and monotonic tension are modeled by an isotropic scalar internal variable D, whose evolution is described using a rate damage law dD/dt = ... governed by visco-plasticity and accounting for the enhancement by stress triaxiality. A novel rate sensitive damage threshold is introduced in order to reproduce the rate dependency of the onset of damaging processes. Damage evolution is coupled with the visco-plasticity model developed by the same authors for single crystal super alloys and accounting for microstructural evolution (like gamma '-rafting and coarsening) in Desmorat et al. (2017). The curves presented in this article are identified at 1050 degrees C for the Ni base single crystal superalloy CMSX-4 but the proposed rate sensitive threshold modeling can be applied to other alloys showing a rate sensitive damage onset, as for example the single crystal superalloys MC2 but also the polycrystalline aggregate AD 730 (TM).