A tensorial thermodynamic framework to account for the γ ' rafting in nickel-based single crystal superalloys

A new model is developed in order to account for the effect of microstructural degradation (i.e. precipitate-directional-coarsening) on the viscoplastic behavior of single crystal superalloys under high temperature exposure. Microstructural changes are modeled by a tensorial description of γ channel width evolution and coupled to the Kelvin modes based viscoplasticity thanks to the Orowan stress. Such a coupling is performed within a thermodynamics framework. Isotropic and directional coarsening of the hardening phase are modeled as well as its dissolution with temperature changes. Results are presented for isothermal creep of CMSX-4 alloy at 1050°C along and crystal directions but the formulation allows to account for anisothermal loadings, isotropization of the creep response at high temperature and misaligned loadings. This newly developed tensorial framework for rafting can also apply to single crystal superalloys having a positive misfit.