铪铝碳陶瓷及复合材料的制备、微观结构与性能表征

IMR OpenIR

	铪铝碳陶瓷及复合材料的制备、微观结构与性能表征
	粘洪强
学位类型	博士
导师	包亦望 ; 周延春
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料学
关键词	超高温陶瓷原位合成力学性能高温刚性 Ultrahigh Termperature Ceramic In Situ Synthesis Mechanical Properties High Temperature Stiffness
摘要	"在Hf-Al-C体系中，我们发现了一种新的三元陶瓷HfAl4C4。采用X射线和高分辨透射电镜分析技术确定了HfAl4C4的晶体结构，并获得了相应的晶格参数及原子位置。以Hf粉、Al粉和C粉为原料在1900oC，用原位反应热压法合成了含有HfAl4C4和Hf2Al4C5的复合材料，并对其微观结构和力学性能进行了研究。Hf-Al-C陶瓷模量低于二元陶瓷HfC，但是它的韧性和强度远远优于HfC。此外，高温模量测试结果表明三元陶瓷具有更优异的高温刚性，在1400oC仍能保持其室温刚性的81%，在1550oC能保持室温刚性的79%，因此是潜在的优良高温结构材料。采用高分辨透射电镜和Z衬度高分辨像技术对Hf-Al-C陶瓷原子尺度的微观结构进行了系统研究。HfAl4C4具有较小的晶粒尺寸和各向异性的晶粒形貌。晶粒内部存在大量的堆垛层错，并有Hf-Al-C陶瓷的多种共生现象。此外，我们首次在三元层状陶瓷中直接观测到了反相畴。高分辨像显示晶粒的晶界没有非晶相的存在。以Hf粉、Al粉和C粉为原料，用原位反应热压法合成了Hf2Al4C5与石墨的复合材料。复合材料由细的长条状Hf2Al4C5和细条及板状石墨晶粒组成。石墨晶粒随着含量的增高趋于团聚，多呈板块状。相比于基体材料，复合材料具有相对低的硬度、强度和模量；但是断裂韧性却得到改善。微观结构分析表明，石墨颗粒起到了扭折和偏转裂纹耗散应力的作用。复合材料具有很好的高温性能，如含有20 vol.%石墨的复合材料在1550oC能保持其室温刚性的93.7%，是优异的高温结构材料。复合材料比单相Hf2[Al(Si)4]C5陶瓷具有更高的比热和热导率。第二相石墨的加入，有利于耗散热应力，从而改善材料抵抗冲击和断裂的能力，因此复合材料具有比基体更好的抗热震性能。以Hf粉、铝粉、Si粉和C粉为原料，用原位反应热压法合成了Hf2Al4C5-SiC的复合材料。复合材料由细的长条状Hf2Al4C5和SiC晶粒组成。SiC的加入抑制了Hf2Al4C5的生长。复合材料中Hf2Al4C5晶粒要比单相Hf2Al4C5陶瓷晶粒细小的多。裂纹在扩展过程中，发生了偏转和桥接，使得断裂过程中耗散了更多的能量。因此，复合材料具有比单相Hf2[Al(Si)4]C5陶瓷更高的硬度，强度和韧性。Hf2Al4C5-30 vol.% SiC复合材料在1550oC能保持较高的刚性，约为其室温刚性的81.2%，是理想的高温结构材料"
其他摘要	" A new ternary carbide, HfAl4C4 was discovered in the Hf-Al-C system. The crystal structure of HfAl4C4 was identified by X-ray diffraction and high resolution TEM image. The crystal parameters and atom positions were also obtained. The microstructure, mechanical properties a Hf-Al-C composite composed of HfAl4C4 and Hf2Al4C5 synthesized at 1900oC using Hf, Al and graphite powders with hot-pressing method were characterized. The composite has higher strength and toughness, bur lower stiffness and hardness compared with HfC at room temperature. The stiffness of composite at 1400oC is close to 81% of that at room temperature. Thus, the excellent stiffness at high temperature makes Hf-Al-C compounds good high-temperature materials. The atomic microstructure of HfAl4C4 was systematically characterized using HRTEM and Z-contrast STEM methods. The microstructure of as-synthesized HfAl4C4 ceramic is composed of fine and elongated grains. There are high densities of stacking faults exhibiting in the grains. And the intergrown structure between HfAl4C4 and Hf2Al4C5 was also observed. Besides, the anti-phase grain boundary was firstly obtained in the ternary layer ceramics. There is no amorphous phase in the grain boundary. Hf2Al4C5-graphite composites have been synthesized at 1900oC by an in suit hot-pressing/ reaction method using Hf, Al and graphite powders as starting materials. The microstructure of as-synthesized composite is composed of fine and elongated Hf2Al4C5 grains and plate-like graphite grains. Compared with matrix, the pomposities show better toughness, but relatively lower strength, stiffness and hardness. The composites have very good high temperature property. The stiffness of Hf2Al4C5-20 vol.% graphite composite at 1500oC is close to 93.7% of that at room temperature. Besides, the composites also have higher heat capacity, thermal conductivity and better thermal shock resistance than the matrix. Hf2Al4C5-SiC composites have been synthesized at 1900oC by an in suit hot-pressing/reaction method using Hf, Al, Si and graphite powders as starting materials. The composite is composed of fine and elongated Hf2Al4C5 grains and plate-like SiC grains. The grain sized of composites is much smaller than the single phase Hf2Al4C5. Thus, the composites have much higher toughness and strength than the matrix at room temperature. Besides, the stiffness of Hf2Al4C5-30 vol.% SiC composite at 1550oC is close to 81.2% of that at room temperature.
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64428
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	粘洪强. 铪铝碳陶瓷及复合材料的制备、微观结构与性能表征[D]. 北京. 中国科学院金属研究所,2012.