Simulation of Creep Crack Growth of a Directionally-solidified Ni-base Superalloy

Creep lifetime of turbine blade material subjected to sustained centrifugal forces at elevated temperatures is limited by accumulated inelastic deformation and creep crack growth (CCG). Creep resistance exhibited in conventionally cast polycrystalline (PC) Ni-base superalloy components has been enhanced via solidification techniques. Directional solidification (DS) results in large grain sizes with limited misorientation at grain boundaries. The present study focuses on a Ni-base superalloy in DS form at 871oC. Data obtained from deformation experiments performed on longitudinal (L) and transverse (T) specimens are used to develop an anisotropic elasto-creep material model. Simulated time-dependent, asymptotic crack tip fields of compact tension (CT) specimens are applied in the calculation of creep zones and fracture parameters, and are discussed in relation to crack growth rate. The microstructure of each CT model differs in terms of grain orientation (i.e., L-T or T-L), crack behavior (i.e., stationary or growing), and other graain attributes. Since each model is subjected to identical loading conditions, effects of microstructural configurations on inelastic deformation are emphasized.