Phase field study of ferroelastic domain switching behavior related to grain size in polycrystalline tetragonal zirconia

t'-YSZ has received widespread attention in the application of thermal barrier coatings due to its ferroelasticity. Related studies have shown that the switching behavior of ferroelastic domains is influenced by grain size (GS), which in turn affects the final toughness of the material. This article constructs a phase field model to study the domain structure evolution and mechanical response of polycrystalline t'-YSZ under external loading. To describe the grain size effect of ferroelastic domain switching, grain boundary (GB) energy is introduced into the phase field model to measure the grain size effect of domain switching. By comparing the results of the uniaxial compression experiment with t'-YSZ, the reliability of our model was verified. The influence of grain size on the microstructure transformation and macroscopic mechanical behavior of ferroelastic domains was studied by considering two geometric models, complete and prefabricated cracks, while further considering the synergistic effect of grain size and grain orientation. The simulation results indicate a negative correlation between GS and coercive stress ${\sigma }_c$. The larger the GS, the higher the overall transformation degree of the ferroelastic domain. The switching of ferroelastic domains is related to grain orientation, and the smaller the grain size, the greater the angle at which the ferroelastic domains do not transform.