晶须自增韧与金属复合耦合增韧氮化硅陶瓷机制的研究

Based on the theory of powder sintering thermodynamics, microstructure design and fracture mechanics, the cermet materials is characterized by static and dynamic microscopic analysis.In this research project, Fe-Mo/Si3N4 cermet is prepared by he heterogeneous precipitation-thermal atmospheric pressure sintering. The Effect of rare earth oxides on micro-structural features and components of Fe-Mo/Si3N4 cermet is analyzed.The common mechanism such as reaction trend between different sintering state and the growth model of Whisker is clarified ..Based on simulation of Whisker growth under multifactorial factors and micro fracture mechanism under applied load, the state of phase combination , the distribution of whisker morphology, matching of the expansion coefficient and the characteristics of Micro-crack nucleation, growth and motion are deepen understanded.the coupled toughening mechanism of silicon nitride ceramic through self-toughening and the of covering nano-metal are discussed on depth. The main purpose of this study aimed at resolving the fatal flaw of such ceramic materials，that is the key mechanism problem of sex crisp, it is very significance to rich and perfect the theory to coupled toughened ceramics using a variety of mechanisms, and to promote the deeper applications of such ceramics.

采用动、静态微观表征，通过粉末烧结热力学、微结构设计与断裂力学理论，分析稀土氧化物等助剂对非均相沉淀-热还原-常压烧结制备核壳结构Fe-Mo/Si3N4金属陶瓷材料微结构特征、组分的影响关系，明晰不同烧结状态晶相之间反应趋势、晶须生长模式等共性机理问题，通过对多因素影响下晶须生长模拟，外加载荷作用该材料的微观断裂机理，深化晶相结合状态、晶须形貌分布、膨胀系数匹配与微裂纹形核、生长及运动特性的内在联系认识，深度探讨自增韧与纳米金属包覆等多种机制耦合增韧氮化硅陶瓷机理。本项目通过研究旨在进一步完善束缚该类陶瓷材料致命缺陷即性本脆的关键机理问题，对丰富和完善多种机制耦合增韧陶瓷理论，推导该类陶瓷的更深层次应用具有重要意义。

Si3N4陶瓷具有高温强度高、抗热震效果好、高温蠕变小、耐腐蚀、密度小等优异性能，在制备极端恶劣条件下零件如航空发动机、切削刀片等具有极为重要的发展前景，但陶瓷脆性问题，成为其进一步应用最大障碍。针对此问题，本论文采用非均相沉淀-还原法制备Fe、Fe-Mo包覆Si3N4陶瓷复合粉末，再添加Mg、Y氧化物，通过相变形式促使材料中本应反应消失的金属相得以保留，实现金属复合增韧；而Mg、Y氧化物在高温形成玻璃相诱导形成晶须状β-Si3N4实现自增韧，从而实现对Si3N4陶瓷的耦合协同增韧，其极大的提高的Si3N4陶瓷强韧性。本项目主要研究该材料烧结工艺-微观组织-性能三者之间的关系规律，通过HSC 热力学计算软件计算多种体系的晶相反应趋势规律（反应可能性、方向、进行程度），获得与实际状态相吻合的反应机制模型。建立了Monte-Carlo晶粒生长程序对β-Si3N4 晶须生长进行模拟，研究了烧结过程微观结构演变机制，揭示了Si3N4陶瓷增韧机理。本项目拓宽了Si3N4陶瓷应用范围，丰富了增韧Si3N4陶瓷理论，并对其它陶瓷增韧具有启示意义，目前实质性的开发新Si3N4陶瓷产品。