Phase Field Modeling Of Transformation Behavior In Tetragonal Zirconia Ceramics

Zirconia ceramics(Y-TZP)possesses excellent mechanical properties,chemical stability and biocompatibility and has significant application potentials in biomedical fields like joint implants,dental restoration,etc.When exposed to water molecules in the human body,the surface layer of Zirconia ceramics is subjected to martensitic phase transformations(also called low temperature degradation),which will cause microcracking in the surface layer.As a result,the service performance of the implant is deteriorated.Proper characterization of the microstructure change of the surface layer induced by the phase transformation and its following impact on the improvement of the service performance of the medical implants through microstructure control and by structural design optimization.Phase field method provide a robust tool to model the phase transformation,crack and diffusion in the material at the mesoscale and within a unified framework.This paper aims to develop a two-dimensional phase-field model to simulate the phase transformation and the diffusion induced phase transformation in the Zirconia ceramics.Firstly,we simulate the phase transformation process in single crystal Zirconia with different crystal orientation by phase-field model,it is found that that the system of single crystal only allows the growth of nuclei in two orientations,parallel to the crystal orientation or perpendicular to the crystal orientation.Secondly,we study the phase transformation process and its effect on transformation toughening in the phase-field model of Zirconia toughening with different crystal orientation and their combinations by phase-field model,it shows that the rate of phase transformation and its effect on transformation toughening are better in 0° crystal orientation than that of the 90 °crystal orientation,and the orientation of the phase transformation is not only affected by its own crystal orientation but also by the adjacent crystal orientation and the free surface.Then,we investigate how the crystalline orientation of surface layer influence the transformation behavior in polycrystalline Zirconia by phase-field model,when the crystalline orientation of surface layer is arranged randomly,the critical chemical driving force required for phase transformation is smaller than when it is arranged in the same orientation,and the orientation of the phase transformation is affected by the adjacent grains and other non-adjacent grains.Finally,we establish the model coupled phase-field model for diffusion and martensitic phase transformation and obtain that the diffusion process of the coupling field can induce the phase transformation process.