Mechanistic short crack growth in single crystal Ni γ − γ microstructure is investigated using Crystal
Plasticity (CPFEM) and eXtended Finite Element Method (XFEM). Maximum slip and stored energy density are hypothesised to be the mechanistic drivers for the crack path and the growth rate that are studied in γ − γ microstructures. This mechanistic basis is shown to capture the effect of γ anomalous yield
strengthening on the crack path and crack growth rate. Crack growth in the γ matrix and shearing of γ
precipitates is predicted to occur at high applied stress at low or high temperature, while low applied
stress is shown to lead to cracks which are confined to the γ channels. Critical stored energies (Gc) are
determined for the γ and γ phases to predict experimentally observed crack growth rate at low temperature and high stress. The crack growth model offers good prediction of both the crystallographic crack
paths and growth rates in γ − γ microstructures, thereby supporting its mechanistic basis.