On the Role of Grain-Boundary Films in Optimizing the Mechanical Properties of Silicon Carbide Ceramics
On the Role of Grain-Boundary Films in Optimizing the Mechanical Properties of Silicon Carbide Ceramics
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DOI：
10.1557/proc-818-n1.1.1
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发表时间：
2004
期刊：
影响因子：
--
通讯作者：
R. Ritchie;X. Zhang;L. Jonghe
中科院分区：
文献类型：
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作者：
R. Ritchie;X. Zhang;L. Jonghe
通过控制晶界结构，主要是纳米晶间膜的性质，通过热压添加铝、硼和碳的β-SiC粉末（ABC-SiC）开发了断裂韧性高达9.1MPa·m的SiC。在这种材料的发展中心一直是系统的透射电子显微镜（TEM）和机械特性。特别是，原子分辨率电子显微镜和纳米探针组合物定量相结合，在分析晶界结构和纳米结构特征。伸长的SiC晶粒与1 nm宽的非晶间膜被认为是负责这种材料的原位增韧，特别是通过裂纹偏转和晶粒桥接的机制。两种方法被认为是有效的，在修改组织和优化力学性能。首先，在1100和1500 ℃之间的温度下规定的退火后处理，导致完全结晶的非晶间膜，并在SiC基体晶粒内引入均匀分散的纳米沉淀物;此外，铝在高温下的晶格扩散被认为是改变晶界组成。其次，还观察到调节烧结添加剂的标称含量以改变ABC-SiC的晶粒形态、晶界结构和相组成。在这方面，个别添加剂在开发边界微观结构的作用进行了鉴定;这被证明是至关重要的优化机械性能，包括断裂韧性和耐疲劳性在环境温度和高温下，弯曲强度，耐磨性，和抗蠕变性。
Through control of the grain-boundary structure, principally in the nature of the nanoscale intergranular films, a silicon carbide with a fracture toughness as high as 9.1 MPa.m has been developed by hot pressing β-SiC powder with aluminum, boron, and carbon additions (ABC-SiC). Central in this material development has been systematic transmission electron microscopy (TEM) and mechanical characterizations. In particular, atomic-resolution electron microscopy and nanoprobe composition quantification were combined in analyzing grain boundary structure and nanoscale structural features. Elongated SiC grains with 1 nm-wide amorphous intergranular films were believed to be responsible for the in situ toughening of this material, specifically by mechanisms of crack deflection and grain bridging. Two methods were found to be effective in modifying microstructure and optimizing mechanical performance. First, prescribed post-annealing treatments at temperatures between 1100 and 1500C were seen to cause full crystallization of the amorphous intergranular films and to introduce uniformly dispersed nanoprecipitates within SiC matrix grains; in addition, lattice diffusion of aluminum at elevated temperatures was seen to alter grain-boundary composition. Second, adjusting the nominal content of sintering additives was also observed to change the grain morphology, the grain-boundary structure, and the phase composition of the ABC-SiC. In this regard, the roles of individual additives in developing boundary microstructures were identified; this was demonstrated to be critical in optimizing the mechanical properties, including fracture toughness and fatigue resistance at ambient and elevated temperatures, flexural strength, wear resistance, and creep resistance.