超细晶YSZ陶瓷电致超塑性拉拔变形机制及工艺控制研究

Based on the unique ionic conductivity and good superplasticity of an ultra-fine crystalline yttria-stabilized zirconia (YSZ) ceramic at elevated temperature, a new idea was proposed, that is the electro-superplastic drawing of YSZ ceramic assisted by the high density impulse current. Nano-sized composite powders will be prepared by the wet chemical method, then sintered subsequently. The ultra-fine grain YSZ ceramic composites with scheduled microstructure can be obtained by the processing controlling. The project will focus on the microstructure characteristics, deformation behavior and forming limit of YSZ ceramic during the electro-superplastic deformation. Moreover, a new way to achieve high strain rate superplasticity by optimizing the conditions of the microstructure, deforming and electric parameters will be explored. The research will reveal the action mechanism of the high density impulse current on the superplastic deformation and its electro-superplastic effect. The experiments will be carried out to make out the rate controlling mechanism, accommodating process and the damaging mechanism of the superplastic forming. Then a macroscopic phenomenological model for electro-superplastic forming of the ultra-fine grain YSZ ceramic will be proposed. The technological parameters and key issues in the electro-superplastic drawing of YSZ ceramic under elevated temperature will be investigated. The work try to clarify the regulation method and the dominating rules to control the drawing technology. The research results could not only enrich the electro-plastic theory, extend the application of the electro-plastic technology, but supply the theoretical and experimental basis for developing the new forming techniques of the superplastic ceramic.

基于超细晶氧化钇稳定的氧化锆陶瓷（YSZ）独有的高温离子导电性和良好超塑性，本项目提出了高能脉冲电流作用下超细晶YSZ陶瓷电致超塑性拉拔变形的新思路。通过湿化学方法制备纳米级复合粉体，采用合理的烧结工艺制备组织结构可控的超细晶YSZ陶瓷。着重研究高能脉冲电流作用下YSZ陶瓷超塑变形过程中的微结构特征、变形行为及成形极限，探索高速超塑变形的组织结构、变形条件和电参量条件的最佳组合方案及其实现途径。揭示脉冲电流在变形中的作用机制和电致超塑性效应，提出电致高速超塑变形的速控机制、协调和损伤机制，建立变形过程的宏观唯象模型。研究YSZ陶瓷高温电致超塑性拉拔工艺及其关键技术，掌握成形过程的一般规律及工艺控制方法。研究结果不仅可以丰富电致塑性理论，拓宽电塑性加工技术的应用领域，且可为开发新的陶瓷超塑成形工艺提供理论和实验依据。

作为典型的高温结构材料，氧化钇稳定的氧化锆陶瓷（Yttria Stabilized Zirconia, 简称YSZ）具有优异的综合性能，常用于制造极端工况下的使役构件。基于YSZ结构陶瓷独特的离子导电性和优良的超塑性，本项目探索了超细晶YSZ陶瓷的电致超塑性及其成形技术。通过对YSZ陶瓷的化学成分及制备工艺的系统研究，获得了具有超细晶组织、高温导电性及良好力学性能的陶瓷材料，包括：1.5mol%Y2O3部分稳定的（m-YSZ+t-YSZ）、3Y-TZP、8Y-CSZ以及氧化物共晶陶瓷。研究了超细晶YSZ陶瓷电致超塑性变形行为，掌握了不同电量参数和变形方案组合下材料的变形行为及成形极限。基于实验中的唯象数据，获得了材料电致超塑变形的本构方程，计算了其变形激活能Q=273kJ/mol、应变速率敏感指数m=0.56、应力指数n=1.8等关键特征参数。获得了材料微观组织结构与力学行为、成形性能之间的规律，提出了YSZ陶瓷电致超塑效应在变形中的作用机制、行为特征及其与超塑性能之间的关系，阐明了电致超塑性成形的物理机制及变形规律。研究表明，YSZ陶瓷在直流电流下的低温超塑性变形机理为扩散蠕变协调的晶界滑移，其低温超塑性变形速率受Zr4+沿着晶界的扩散所控制。对比分析了YSZ陶瓷超塑性变形前后的组织、性能的变化，提出了新的材料微结构分析方法，该方法可以在微米尺度精确解析陶瓷材料特征组织结构的取向和晶体学取向。发展了电致塑性快速成形技术，初步探索了电塑性成形在钛合金、高温合金等难变形材料成形领域的应用。本项目研究结果已在国际主流期刊Script Materialia、Journal of the American Ceramic Society、Journal of the European Ceramic Society、Ceramics International、Materials Science and Engineering A发表学术论文13篇。申请了国内发明专利4项，国际PCT专利申请1项，其中已获批国家发明专利3项。完成了学术专著《陶瓷材料微观组织形成理论》（科学出版社出版）1部。上述研究成果不仅拓展了电塑性理论及其应用，也为陶瓷等难变形材料及其构件的电致超塑成形提供了理论基础和实验依据。