Improvement of superplasticity in ceramics due to grain boundary control

研究结果总结如下。(1)β-锂辉石玻璃掺杂TZP的超塑性表现为晶界玻璃相的存在降低了高温流动应力，拉伸塑性并不是由流动应力引起的，而是由ZrO_2晶粒与玻璃相之间的界面性质决定的。(2)SiO_2的掺杂大大增强了TZP的超塑性。SiO_2相中的少量掺杂会降低材料的塑性。分析掺杂对晶界结构和化学键合状态的影响是十分必要的。(3)SiO_2掺杂TZP的晶界角或结处存在非晶SiO_2相，而晶界面处不存在。Si^<4+>离子在晶界面偏聚，但不形成非晶膜. (4)TiO_2掺杂的TZP具有独特的超塑性流动行为，TiO_2的掺杂导致晶粒尺寸增大，但流动应力降低，塑性提高。本文从现象学的角度对这种独特的行为进行了解释。(5)发现了Al_2O_3基陶瓷超塑性流动的新的实验证据。理解晶界结构和化学对解释结果是重要的。

The research results are summarized as follows.(1) Superplasticity in beta-spodumene glass-doped TZP exhibits that the high-temperature flow stress is reduced by the presence of grain boundary glass phase, and that the tensile ductility is not simply caused by flow stress but is determined by the nature of interfaces between ZrO_2 grain and glass phase.(2) Superplasticity in TZP is highly enhanced by SiO_2-doping. However the ductility is deteriorated by small dopant in SiO_2 phase. It is essential to analyze the change of grain boundary structure and chemical bonding state with dopant.(3) Amorphous SiO_2 phase is present in grain boundary corners or junctions of SiO_2-doped TZP but not in grain boundary faces. Si^<4+> ions segregate in grain boundary faces but does not form amorphous film.(4) A unique superplastic flow behavior is founf in TiO_2-doped TZP.TiO_2-doping results in grain size increment but in the reduction of flow stress and the improved ductility. A phenomenological analysis is made to explain the unique behavior.(5) New experimental evidence is found in superplastic flow in Al_2O_3-base ceramics. It is important to understand the grain boundary structure and chemistry to explain the results.