金属熔体环境下可加工复相陶瓷的热震损伤和微区增韧机理

In many high temperature metal melt environments, both higher strength and excellent thermal shock resistance should be necessary for materials. By traditional theory, the both higher strength and the excellent thermal shock resistance were contradict, and it was difficult to obtain one material with both these two good properties. In recently research, it was found that the machinable ceramic composites with nano sized h-BN had both higher strength and excellent thermal shock resistance. It was because that the soft layer phase (h-BN and h-C) would fracture in micro-zone and toughen. In this research, concept of toughen in micro-zone for machinable ceramic composites with soft layer phase will be developed. Layers slip，micro-zone fracture, layers tearing and mechanism of energy absorbing will be study by electron microscope with in situ indentation load and thermal shock test in metal melt. The mechanisms of thermal damage and micro-zone toughen for machinable ceramic composites in metal melt will be clear by mechanical properties test, fracture mechanics analysis and finite element calculation. By this research, the design rules for higher thermal shock resistance materials used in metal melt will be developed, and it can be provided the theoretical direction for the use of machinable ceramics composites in metal melt environment.

很多用于金属熔体中的高温陶瓷部件，要求材料同时具有较高的强度和优异的热冲击性能。从陶瓷传统热冲击理论来看，高强度和优异热冲击性能存在矛盾，很难兼顾。我们近期研究发现，含六方氮化硼等层状弱相的纳米复相可加工陶瓷，在具有可加工性能的同时，还具有高强度和优异的热震抗力，其根源与可加工陶瓷中层状弱相(h-BN,石墨等)在熔体热震过程中的微区变形、断裂与增韧有关。本项目提出含层状弱相复相可加工陶瓷的"微区增韧"概念，通过电镜内原位压痕加载和金属熔体热冲击模拟实验，研究层状弱相在局域应力作用下的滑移、微区内的断裂、层裂行为及其能量吸收和应力释放机制。通过宏观微观实验观察、断裂力学分析及有限元模拟计算,澄清金属熔体中可加工复相陶瓷热震损伤和微区增韧机理。通过本项目研究，将为金属熔体应用环境下的高强度、抗热冲击陶瓷材料提供性能优化原则，确定最优的组织结构，为可加工复相陶瓷在金属熔体中应用提供理论指导。

SiC、β-SiAlON等材料具有优良的室温和高温力学性能以及对金属熔液的惰性，但传统的制备方法的高成本及陶瓷材料的抗热震性的不足，制约了材料的应用。传统方法提高材料的抗热震损伤能力一般要大幅降低材料的强度。用于金属熔体中的高温陶瓷部件，要求材料同时具有较高的强度和优异的热冲击性能。从陶瓷传统热冲击理论来看，高强度和优异热冲击性能存在矛盾，很难兼顾。通过研究发现，含六方氮化硼等层状弱相的纳米复相可加工陶瓷，在具有可加工性能的同时，还具有高强度和优异的热震抗力，其根源与可加工陶瓷中层状弱相(h-BN,石墨等)在熔体热震过程中的微区变形、断裂与增韧有关。本项目提出含层状弱相复相可加工陶瓷的“微区增韧”概念，通过电镜内原位压痕加载和金属熔体热冲击模拟实验，研究了层状弱相在局域应力作用下的滑移、微区内的断裂、层裂行为及其能量吸收和应力释放机制。通过宏观微观实验观察、断裂力学分析及有限元模拟计算,建立了裂纹扩展模型，澄清金属熔体中可加工复相陶瓷热震损伤和微区增韧机理。通过本项目研究，为金属熔体应用环境下的高强度、抗热冲击陶瓷材料提供性能优化原则，确定最优的组织结构，为可加工复相陶瓷在金属熔体中应用提供理论指导。