【作者】 李垚；

【导师】 韩杰才； 张幸红；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2006， 硕士

【摘要】 先进的超高温陶瓷材料具有优异的高温强度和抗氧化性等特点,使其能够胜任于包括高超声速长时飞行、大气层再入、跨大气层飞行和火箭推进系统等极端环境。本文采用真空热压烧结工艺制备了ZrB₂+20%SiC、ZrB₂+25vol%SiC、ZrB₂+30vol%SiC和ZrB₂+20vol%SiC+20vol%ZrC四种陶瓷基复合材料,利用SEM、EDS等手段对其组织和相成分进行了分析,并对其力学性能进行了测试。对几种复合材料在室温～2500℃温度区间内的热冲击行为进行了研究。所制备的ZrB₂/SiC/ZrC体系复合材料,ZrB₂+20%SiC抗弯强度和断裂韧性分别是470MPa和5.21MPa·m^1/2、ZrB₂+25vol%SiC分别为520MPa和5.26MPa?m1/2 , ZrB₂+30vol%SiC分别为672MPa和5.32MPa·m^1/2、ZrB₂+20vol%SiC+20vol%ZrC分别为702MPa和5.22MPa·m^1/2,比纯ZrB₂材料相比有很大的提高。在ZrB₂基陶瓷复合材料中,SiC的加入阻碍了ZrB₂的过分长大,细化了晶粒组织,改变了材料的断裂模式,由完全的穿晶断裂变为混合的沿晶/穿晶断裂。ZrB₂/SiC的强化机制是晶粒的细化,韧化机制是裂纹的偏转/分解和晶粒的细化。由于ZrB₂的（001）面和ZrC的（110）面有很好的化学相容性,在ZrB₂/SiC材料中添加20vol%ZrC,这会在很大程度上增加它们的烧结性能和提高它们的机械性能。通过对材料进行热冲击损伤的数值模拟,得出试样的中心存在较大的压应力,边缘存在相当大的拉应力,最大拉应力发生在周边区域。氧-乙炔火焰热冲击实验的结果表明: ZrB₂+30vol%SiC的抗热冲击性能最好。ZrB₂/SiC体系复合材料中随SiC含量的增加,抗热冲击性能逐渐提高。ZrC的加入虽然对材料烧结性能和力学性能的提高起到理想的作用,但对提高抗热冲击性能并未得到很好效果。热处理对提高材料的抗热冲击性能起到很好的作用。更多还原

【Abstract】 The characteristics of advanced ultra-high temperature ceramics （UHTCs）, such as strength at high temperature and oxidation resistance, allow them to be used in extreme environments including those associated with hypersonic flight, atmospheric re-entry, and rocket propulsion. ZrB₂+20vol%SiC, ZrB₂+25vol%SiC, ZrB₂+30vol%SiC and ZrB₂+20vol%SiC+20vol%ZrC composites were prepared by hot-pressing with vacuum. The microstructures and phase constitutions of the composites were investigated by the means SEM, EDS etc.. Mechanical properties of the composites were tested. The thermal shock behaviors of the selected materials was analyzed and observed at high temperature from room temperature to 2500℃.The flexural strength and fracture toughness of ZrB₂/SiC/ZrC composite which were produced successfully:ZrB₂+20vol%SiC are 470MPa and 5.21 MPa?m 1/2 ,ZrB₂+25vol%SiC are 520MPa and 5.26MPa?m 1/2, ZrB₂+30vol%SiC 672MPa and 5.32MPa·m^1/2 and ZrB₂+20vol%SiC+20vol%ZrC ceramic are 702MPa and 5.22 MPa·m^1/2 respectively. For the ZrB₂ based composites, with the addition of SiC particles, the excessive growth of ZrB₂ materials is restricted and grain structure is refined. Meanwhile the fracture modes are changed, namely, from transcrystalline to mixed transcrystalline/ intercrystalline. For the ZrB₂/SiC ceramic, strengthening mechanisms is grain refining and the toughening mechanism is crack deflection/decomposition and grain refining. The strength of ZrB₂/SiC materials are further improved by addition of 20vol%ZrC, because of the chemical consistency between the crystal （001） of ZrB₂ and the crystal （110） of ZrC. The addition of ZrC improved the sintering and mechanical properties of ZrB₂/SiC composite effectively.The simulation of thermal shock showed that there was compression stress in the middle of sample, and tension stress at the edge of sample. Results of thermal shock in the temperature range from room temperature to 2500℃indicated that of ZrB₂+30vol%SiC is the best. The addition of ZrC improved the sintering and mechanical properties of ZrB₂/SiC composite, but didn’t show excellent thermal shock resistance. The heating processing increased thermal更多还原