近零膨胀ZrO2/ZrW2O8防热复合材料的实现机制与实验验证

Structure stability, safety and reliability of the high temperature parts will be decreased, and their thermal protection and thermal shock resistance will be weakened or even destroyed because of large thermal expansion and cold contraction in the high temperature structural ceramics such as ZrO2. The most effective way to control the thermal expansion behavior of ZrO2 ceramic is to combine with the ZrW2O8 material with negative thermal expansion in order to obtain the properties of low expansion or even zero expansion by use of the superposition effect. This project studies thermal shrink and transformation mechanism of the ZrW2O8 ceramic and establishes their relationships in order to lay the foundation for stable transformation and raise of the use temperature in the ZrW2O8 ceramic with the negative thermal expansion. After studying the implementation mechanism of the ZrO2/ZrW2O8 ceramic matrix composites with near zero expansion, we will establish the nonlinear relationships between thermal expansion coefficient and the composite components from the micro model of atomic lattice level. The ZrO2/ZrW2O8 ceramic matrix composites with controllable thermal expansion coefficient have been prepared by powder metallurgy technology, and the research on their microstructure and properties is completed. The experimental results verify the correctness of the theory design, so as to investigate the physical mechanism of the ZrO2/ZrW2O8 ceramic matrix composites with near zero expansion coefficient, good strength/toughness and thermal shock resistance, to strive for a breakthrough in the basic application researches of the ceramic matrix composites with near zero expansion, and to provide a theoretical basis and technical support for the practical application of ZrO2/ZrW2O8 ceramic matrix composites.

ZrO2等高温结构陶瓷具有较大的热胀冷缩会降低高温零部件的结构稳定性和安全可靠性，削弱甚至破坏材料的防热与抗热冲击能力。调控ZrO2陶瓷热膨胀行为最行之有效的方法，就是与具有负热膨胀ZrW2O8材料进行复合，利用叠加效应获得低膨胀、甚至零膨胀性能。项目研究ZrW2O8陶瓷的热缩与相变机理，建立两者之间的关系，为稳定相变、提高负膨胀陶瓷的使用温度奠定基础；研究近零膨胀ZrO2/ZrW2O8陶瓷复合材料的实现机制，从原子晶胞层次构建相应的微观模型，确立复合材料成分-热膨胀系数的非线性关系；采用粉末冶金工艺制备热膨胀可控的ZrO2/ZrW2O8复合材料，完成材料的性能与组织研究，并与理论设计的结果进行印证。探讨近零膨胀ZrO2/ZrW2O8陶瓷复合材料强韧性好、抗热冲击的物理机制，争取在近零膨胀陶瓷基复合材料应用基础研究方面有所突破，为此类材料的实际应用提供理论基础与技术支撑！

为了降低甚至抵消ZrO2等高温结构陶瓷的热胀冷缩效应对零部件结构稳定性和安全可靠性的破坏，亟需研究ZrW2O8与ZrO2复合以制备低膨胀乃至近零膨胀复合材料。项目通过第一性原理与分子动力学理论，研究了ZrW2O8的声子、热力学性质；通过ZrW2O8的相变失稳分解和高温相变合成实验研究了ZrW2O8的相变规律，并与ZrW2O8的热缩机制建立了关联；采用复合材料热学/力学性能预测模型研究了ZrO2/ZrW2O8成分-热膨胀性能非线性关系，结合实验表征给出了非线性关系的本质；分别采用固相高温烧结法和水热辅助冷烧结工艺制备获得了低膨胀/近零膨胀ZrO2/ZrW2O8陶瓷复合材料材料，实现了复合材料由多孔到致密的调控，研究了ZrW2O8和ZrO2/ZrW2O8冷烧结过程的致密化过程，建立了冷烧结机制；通过水热法设计ZrO2与ZrW2O8两相界面的结合方式，制备自组装ZrO2-ZrW2O8镶嵌结构复合材料粉体，同时结合冷烧结过程中添加的水性液相，解决了两相热失配的问题。本项目的研究从机制上揭示了近零膨胀ZrO2/ZrW2O8复合材料的实现机制，攻克了该类陶瓷复合材料领域长期存在的钨酸锆亚稳相高温易分解、尺寸效应导致固相法难以制备大尺寸试件、ZrO2/ZrW2O8异相界面热应力失配等三个主要瓶颈难题，为近零膨胀ZrO2/ZrW2O8复合材料尽快实现工程化应用提供了理论基础与技术支撑。