SUMMARY

Nickel-base superalloys have remained the premier material to use for extreme temperature applications in turbines. Because of their composite microstructure, which is primarily a L12 precipitate phase in a matrix phase, many complex deformation mechanisms arise 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 physics-based Crystal Viscoplasticity model is proposed for the creep-fatigue interactions in single-crystal superalloys. In the model, the equations used to describe the deformation mechanisms are unique to each material phase which allows for modeling of the different deformation mechanisms in a single unit cell. Finally, a novel constrained Newton-Raphson integration scheme is also proposed that enables quick implementation of the model in an Abaqus User Material 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