医用氧化锆陶瓷表面退化和失效的微观机理及其实验和相场法研究

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 deterioated. Proper characterization of the microstructure change of the surface layer induced by the phase transformation and its following impact on the mechanical properties of the zirconia ceramics is important for the improvement of the service performance of the medical implant through microstructure control and by structural design optimization. Phase field microelasticity and its related numerical method provide a robust tool to model the phase transformation, microcrack nucleation and main crack propagation in the material at the mesoscale and within a unified framework.This project aims to develop a unified numerical method within the framework of phase field microelasticity to model the water induced phase transformation and microcrack nucleation process in the surface layer of the zirconia ceramics and study how the stress and microstructure factors such as the crystalline orientation of the surface layer influence the low temperature degradation process. The project also aims to characterize the microstructure change in the surface layer and assess the mechanical performance of the zirconia ceramics after its low temperature degradation by combining numerical simulations with experimental observations and testing.It is expected that the intrinsic relationship between the microstructure,water induced phase transformation and the mechanical performance of the ceramics can be revealed through this study. We also expect that the research results of this study can be useful to guide the biomedical application of the zirconia ceramics.

氧化锆陶瓷（Y-TZP）具有优良的力学性能、化学稳定性和生物相容性，在关节置换和牙科修复等医学领域具有重要应用前景。在人体环境下，氧化锆陶瓷表层易发生水分子诱导相变（又称低温退化），致使表层产生微裂纹，从而影响置换物的服役性能。合理表征低温退化后表层微结构的改变及其对氧化锆陶瓷力学性能的影响对于从微结构调控和结构设计角度提高置换物的服役性能具有重要意义。相场微弹性方法可在介观尺度统一模拟材料内部相变、微裂纹萌生和主裂纹扩展等微观过程的耦合作用机理。本项目致力于在该框架下，发展通用的数值方法，对氧化锆陶瓷表层的水诱导相变和微裂纹萌生过程进行模拟，探讨表层应力和晶体取向等微结构因素对低温退化过程的影响；结合实验观测和测试，对低温退化后氧化锆陶瓷表层的微结构改变进行表征，并对其力学性能进行评估，以从机理上揭示材料微结构、水诱导相变和力学性能之间的内在联系，为氧化锆陶瓷的医学应用提供参考依据。

氧化锆陶瓷（Y-TZP）具有优良的力学性能、化学稳定性和生物相容性，在关节置换和牙科修复等医学领域具有重要应用前景。在人体环境下，氧化锆陶瓷表层易发生水分子诱导相变（又称低温退化），致使表层产生微裂纹，从而影响置换物的服役性能。本项目致力于发展相应的相场模型，结合实验观测和测试，对低温退化后氧化锆陶瓷表层的微结构改变进行表征，并评估其力学性能，以从机理上揭示材料微结构、水诱导相变和力学性能之间的内在联系，为氧化锆陶瓷的医学应用提供参考依据。. 在基金资助下，申请人团队具体开展了如下研究工作：（1）发展了模拟氧化锆陶瓷t-m相变的相场模型，对四方相氧化锆单晶和多晶中的自发相变和应力诱导相变过程进行了模拟,对相变后氧化锆陶瓷的微结构特征进行了表征，讨论了边界条件、晶体取向和晶粒尺寸等因素的影响；（2）构造了模拟t-m相变和裂纹扩展的耦合相场模型，模拟了四方相氧化锆单晶中裂纹扩展时的相变增韧现象以及四方相氧化锆多晶中相变诱导晶界微裂纹现象。多晶相场模型的模拟结果和文献中报导的实验观测结果吻合。该耦合相场模型是首次从介观尺度定量研究氧化锆陶瓷的相变增韧效应并对氧化锆陶瓷低温退化后的微结构特征进行表征；（3）建立了马氏体变体的向错偶极子模型，采用理论模型分析了马氏体变体受晶界阻碍时诱导晶界微裂纹形核的临界宽度；（4）在多晶相场模型中引入了晶界能变化的影响，探讨了晶粒尺寸对氧化锆多晶体自发相变和应力诱导相变的影响，得到了四方相氧化锆陶瓷呈现超弹性和形状记忆效应时的应力-应变曲线；（5）编制了氧化锆陶瓷本构模型的UMAT子程序，放弃传统的小相变区域假设，采用内聚力单元和三维有限元模型模拟了氧化锆陶瓷内边裂纹和界面裂纹的相变增韧效应，探讨了应力状态、界面性质和材料参数对相变区域和增韧效应的影响；（6）制备了氧化锆陶瓷试样，并对试样进行了SEM观测和XRD扫描以及低温退化实验和压痕断裂韧性测试，为相场模拟提供了材料微结构信息，从实验角度证实了低温退化对表层断裂韧性的影响。实验研究发现试样表面打磨形成的表层晶体织构可显著提高氧化锆陶瓷的低温退化性能。以上研究结果从介观尺度揭示了氧化锆陶瓷的低温退化机理，为氧化锆陶瓷置换物的设计和加工提供了参考依据，同时也为氧化锆陶瓷在低温退化后的表层微观结构表征以及力学性能评估提供了定量分析工具。

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