Si_(3)N_(4)陶瓷材料晶界特征分布研究

Grain boundary character distributions in Si_(3)N_(4)ceramics

晶界的结构对氮化硅陶瓷材料的物理和化学性能、特别是高温力学性能有重要影响.本文利用基于电子背散射衍射技术、体视学及统计学的五参数分析法研究了国产和国外产热等静压烧结的商用氮化硅轴承球样品的晶界特征分布.结果表明,两个样品的晶界取向差分布均在约180°处出现异常,相关晶界占总晶界的比例明显高于随机分布,其取向差主要包括[0 1-1 0]/180°和[-1 2-1 0]/180°,分别对应Σ2和Σ3晶界.两个样品中的Σ2晶界的界面匹配基本一致,均以{0 0 0 1}/{0 0 0 1}基面/基面匹配为主,但二者Σ3晶界的界面匹配存在很大差异,表现为国产样品以{-1 2-1 0}/{-1 2-1 0}柱面匹配为主,而国外产样品以{1 0-1 0}/{1 0-1 0}柱面匹配为主;具有{-1 2-1 0}/{-1 2-1 0},{0 0 0 1}/{0 0 0 1}和{1 0-1 0}/{1 0-1 0}三种界面匹配特征的晶界,其面重合点密度分别为2.45/nm^(2),7.95/nm^(2)和9.10/nm^(2),晶界的结构有序度依次升高.分析指出,具有{1 0-1 0}/{1 0-1 0}界面匹配特征的Σ3晶界以及具有{0 0 0 1}/{0 0 0 1}界面匹配特征的Σ2晶界是氮化硅陶瓷材料中的一类特殊晶界.

The structure of grain boundary has an essential influence on the physical and mechanical properties,especially the high-temperature mechanical properties of silicon nitride ceramics.In the present work,the fiveparameter analysis method which is established based on electron backscatter diffraction(EBSD),and stereology and statistics are used to study the grain boundary character distributions in the two commercial silicon nitride ceramic ball samples.These two samples are both fabricated by hot isostatic pressing but made in China and abroad,respectively.The results indicate that the misorientation distributions of the two samples radically deviate from the random distribution at a rotation angle of 180°,showing that the frequency of the relevant grain boundaries is dramatically higher than that of the randomly distributed ones.These grain boundaries are mainly those possessing the misorientations of [0 1-1 0]/180° and [-1 2-1 0]/180°,corresponding to Σ2 and Σ3 boundaries,respectively.The grain boundary inter-connections(GBICs) of the Σ2 boundaries are basically the same in the two samples,and they are dominated mainly by the {0 0 0 1}/{0 0 01} basal-to-basal inter-connection.However,the GBICs of Σ3 boundaries are quite different in the two samples.they primarily the {-1 2-1 0}/{-1 2-1 0} prismatic-to-prismatic inter-connection for the Σ3 boundaries in the sample made in China,but it is mainly the {1 0-1 0}/{1 0-1 0} prismatic-to-prismatic inter-connection for theΣ3 boundary in the sample made abroad.Crystallographic analysis shows that the planar coincidence site density(PCSD) for the {-1 2-1 0}/{-1 2-1 0},{0 0 0 1}/{0 0 0 1} and {1 0-1 0}/{1 0-1 0} GBIC are2.45/nm^(2),7.95/nm^(2) and 9.10/nm^(2),respectively,implying that the degree of the structural ordering increases in turn.Further discussion emphasizes that the grain boundaries possessing {1 0-1 0}/{1 0-1 0} GBIC and{0 0 0 1}/{0 0 0 1} GBIC should be one type of special boundaries due to their high degrees of structural ordering.