ZrB2基陶瓷超塑成形过程液相行为控制机理研究

ZrB2-based ultra-high temperature ceramics have been proved to be the preferred materials to withstand extreme environments such as ultra-high temperature, load and oxidation. However, the lack of effective forming method has been an important factor restricting the application of complex shape components. A new near-net forming processing named ‘controllable liquid phase’-assisted ZrB2-based ceramic superplastic deformation is proposed in this project to solve the poor deformation ability in the ZrB2-based ceramics. In order to ensure the high temperature mechanical properties, the liquid phase will be removed from the final ceramics by finely controlling the processing technology and species of additives. We will take this project from three aspects, named, liquid phase-assisted superplasticity, liquid phase removal methods, and the relationship between microstructures and mechanical properties at high temperature. The aim of this project is clarifying the superplastic deformation mechanism of the ZrB2-based ceramics with the assistance of the liquid phases, verifying the influence factors and controlling methods of the liquid phase removal, illuminating the relationship between the microstructures and mechanical properties at high temperature, clarifying the controlling mechanism of the liquid phase behavior during the superplastic forming process, and finally establishing the control methods. The achievements will provide the theoretical foundation and experimental basis for the ‘controllable liquid phase’-assisted ZrB2-based ceramics superplastic forming.

ZrB2基超高温陶瓷已被证明是超高温、载荷、氧化等极端环境下服役的首选材料，但缺乏有效的成形加工方法已成为制约该材料复杂形状构件工业应用的重要因素。本项目针对ZrB2陶瓷成形能力差的问题，提出了“可控液相”辅助下ZrB2基陶瓷超塑近净成形的新思路，即，通过优化设计添加剂及精细调控成形和后处理工艺，实现ZrB2陶瓷液相辅助超塑近净成形，随后基于碳热反应转化消除材料内部残留液相，以确保其高温力学性能！本项目拟从液相辅助超塑成形条件、液相转化调控方法、组织性能关系三个层次展开研究。旨在明确液相辅助ZrB2陶瓷超塑成形的变形行为，探明液相转化的影响因素，阐明材料微观组织与高温力学性能的内在联系，掌握ZrB2基陶瓷超塑成形过程及变形后液相行为的控制机理，提出液相行为控制方法，最终解决材料在超塑成形和服役环境下对液相需求不同的问题，为“可控液相”辅助ZrB2基陶瓷的超塑成形技术提供理论基础和实验依据。

ZrB2超高温陶瓷具有极其优异的高温力学性能和抗氧化、抗烧蚀等热物理性能，已被证实是在超高温/氧化/载荷极端环境下服役的首选材料，可应用于高超声速飞行器鼻锥、翼前缘、发动机喉衬等关键部件。本项目针对ZrB2陶瓷复杂构件成形困难的瓶颈问题，提出了“可控液相”辅助下ZrB2基陶瓷超塑近净成形的新思路，通过在ZrB2中添加ZrSi2的方式调控陶瓷的制备工艺及微观组织，获得具有高速/低温超塑成形能力的陶瓷材料，包括：ZrB2-10ZrSi2、ZrB2-20ZrSi2和ZrB2-30ZrSi2。研究了该类材料在不同应变速率和变形温度条件下的变形行为，掌握了不同ZrSi2添加量和变形工艺参数下的变形行为及成形能力。基于实验唯象数据，获得了材料超塑性变形的本构方程，计算其变形激活能Q=209 kJ/mol，应力指数n=2.38。结合其变形行为和特征参数结果，阐释了液相辅助在ZrB2陶瓷超塑性变形中的作用机制，明确了ZrB2-30ZrSi2的变形机制主要受晶界滑移和晶粒转动控制。利用碳热还原反应消除了ZrB2陶瓷中的ZrSi2残留，研究结果表明，当热处理温度达到1600°C，保温时间达到2h，ZrSi2可接近完全消除，进而可以改善成形陶瓷材料的高温力学性能。本项目的研究结果在国内外主流期刊Journal of the European Ceramic Society、Materials Science and Engineering A、Ceramics International发表SCI论文7篇；申请国家发明专利7项，目前已授权6项，1项已公开；合著完成了《陶瓷材料微观组织形成理论》学术著作（科学出版社出版）1部，发表英文学术专著《Superplastic deformation and electric field assisted joining of advanced ceramics》（Elsevier Publisher）1章。上述研究成果不仅为“可控液相”辅助ZrB2基超高温陶瓷的超塑成形技术提供理论基础和实验依据，同时也丰富了陶瓷材料微观组织形成、超塑性成形及连接的理论内涵。