High-pressure turbine blades are critical components of aircraft engines. They are cast as single-crystals of nickel-base superalloys. A negative side effect is the formation of casting micropores initiating fatigue failure during service. The pores can be removed by hot isostatic pressing (HIP) performed at temperature close to solidus. However, pore annihilation in single-crystals is a complex multiscale physical process, which is still poorly understood. In this work, two phase-field models are developed to analyze important driving forces in this process.
First, a phase-field model of dislocations is developed with a discretization scheme that explicitly captures the face-centered cubic geometry and allows considering strongly heterogeneous materials and sharp interfaces without generating numerical artifacts. The model reproduces dislocation glide, junction formation and a particular attention is devoted to the dislocation core behaviors. The model is applied to analyze the evolution of dislocations in the vicinity of a pore in HIP conditions. We show that the anisotropy of the elastic tensor impacts the microstructure evolution and that dislocations evolve to align their edge component along a <111> direction.
Second, a phase field model is developed to analyze the climb of edge dislocations in the vicinity of the pore. The model includes vacancy diffusion, dislocation climb as well as surface tension of the pore. The model is implemented in Fourier space, and simulations are performed to analyze the kinetics of the pore annihilation. Finally, the results are compared to experiments performed in the CMSX-4 nickel-base superalloy.