【摘要】 超高温陶瓷复合材料主要由ZrB2,ZrC,HfB2,HfN,HfC,TaC等过渡族难熔硼化物、碳化物和氮化物组成,这些材料的熔点高于3000℃,是一类非常重要的高温结构材料,近年来在基础研究和技术应用方面均受到了极大的关注.在超高温陶瓷复合材料家族中,ZrB2-SiC和Hf B2-SiC基超高温陶瓷复合材料因具有优异的综合性能,包括优异的抗氧化/烧蚀性能、良好的高温强度保持率和适中的抗热冲击性能,可以在2000℃以上的氧化环境中长时间使用.这些独特的性能使得它们成为高超音速飞行、再入大气层和火箭推进等极端环境下使用的最有前景的候选材料.本文对超高温陶瓷复合材料的制备、力学性能、抗热冲击性能、抗氧化/烧蚀性能和热响应进行了全面的综述.对超高温陶瓷复合材料组分、微结构和性能之间的关系进行了详细的讨论,同时添加剂对材料性能的影响也进行了讨论,这为超高温陶瓷复合材料在特定使用环境的综合性能的优化提供了有效的设计原则和方法.此外,本文还指出了超高温陶瓷复合材料目前存在的挑战,并对未来的发展趋势作了展望.更多还原

【Abstract】 Ultra-high temperature ceramics(UHTCs) are composed of ZrC, ZrB2, HfC, HfB2, HfN and TaC and their melting points are higher than 3000°C. They are a vital class of high temperature structural materials and have attracted a great deal of attention in the past two decades in fundamental research and in technological applications. The ZrB2-SiC and Hf B2-SiC UHTC composites, in particular, have excellent oxidation/ablation resistance, moderate thermal shock resistance and high strength retention at elevated temperature. They can survive oxidizing environments at temperatures of 2000°C and higher. These properties make them the most promising materials for use in extreme environments such as hypersonic flight, atmospheric re-entry, and rocket propulsion. ZrB2-based and HfB2-based UHTCs have similar oxidation and ablation behaviors however as Z B2-based UHTCs are lighter and less expensive, they are used as aerospace materials. Here we provide a comprehensive review of UHTC composites including their preparation, mechanical properties, thermal shock resistance, oxidation/ablation properties and thermal response, with a particular focus on ZrB2-based UHTCs. UHTCs were generally fabricated by hot pressing, spark plasma sintering, pressureless sintering, reactive hot pressing and sinter forging. Hot pressing is the dominant densification technique for the preparation of UHTCs. The flexural strength of UHTCs decreases with an increase in grain size and it exhibits a strong correlation with the size of the Si C particulates. However, the fracture toughness trend is not consistent with that of strength and therefore the matching of grain size becomes important. UHTCs display plasticity at elevated temperature and their brittle-to-ductile transition temperature(1500°C) strongly depends on the grain size and the purity of the grain boundaries. Catastrophic failure occurs easily during the heating or cooling process. The thermal shock resistance of UHTCs is a major issue for future applications. The methods used to improve the thermal shock resistance of UHTCs are summarized from critical thermal shock temperature and strength retention rate after thermal shock testing points of view. The oxidation behavior of UHTCs significantly depends on the temperature and the temperature limits of the applications of these materials are analyzed. The effect of the additives on the overall performance of the resultant composites as well as the relationship between material composition, microstructure and performance are also discussed in detail. This provides useful insights into effective design principles to optimize the overall structural performance of ultra-high temperature ceramic composites according to special service environments. The remaining challenges and future outlook of this field are also addressed.更多还原