SUMMARY

Nickel-base superalloys have remained the premier material to use for extreme temperature applications in turbine engines. At the microstructure scale of relevance, superalloys are a composite material comprised of a L12 precipitate phase and a disordered matrix phase. Many complex deformation mechanisms are present and are not typically modeled in commercial finite element solvers used to design turbine components. Accounting for the distinct deformation mechanisms that take place at the microstructure level is of crucial importance to properly model creep, fatigue, and creep-fatigue interactions to which modern turbine components are subject. In this research a novel physics-based Crystal Viscoplasticity model is developed for the creep-fatigue interactions in single-crystal superalloys. In the model, the equations used to describe the deformation mechanisms are distinct to each material phase. The model is implemented as an Abaqus User Material (UMAT) Subroutine which models the 2-phase microstructure by separating the contributions of each material phase in the inelastic velocity gradient. This allows direct implementation of the model in commercially available finite element solvers thus enabling the analysis of 3-dimensional components under realistic boundary conditions. Finally, the model material parameters are exercised to study the effect changes in microstructure features have on the creep-fatigue response of the alloy in order to provide insights that can be useful in alloy and component design.