Development of the evaluation Method for High Temperature Strength of Silicon Nitride

本研究的目的是建立适当和精确的方法来评估氮化硅陶瓷在室温和高温下的强度和韧性。该研究于1986年至1987年在立命馆大学科学与工程学院进行。1986年，设计并制作了在单调拉伸和三点弯曲载荷条件下的强度测试装置。在每种情况下，都要注意获得负载传递路径的精确对准。利用研制的加载设备，在室温和高达1300℃的高温条件下，对多个氮化硅陶瓷试样进行了系统的实验。对试验结果进行了统计分析，主要讨论了以下两点：(1) Weibull参数的温度依赖性；(2)单调拉伸和三点弯曲载荷条件下强度的统计特性。1987年，继续进行了前一年的实验，对两年的实验结果进行了总结和讨论，建立了氮化硅陶瓷在室温和高温下强度和韧性的评价方法。除上述结果外，得到的结果如下：(3)考虑有效体积概念时，两种载荷条件下的强度具有较好的相关性；(4)考虑高温下裂纹扩展缓慢导致的裂纹长度增量时，高温下的断裂韧性与室温下的断裂韧性值相同；(5)对于氮化硅中存在的小尺寸固有缺陷，线性断裂力学概念似乎也适用于断裂准则。以断口原点附近偏析铁区尺寸为缺陷尺寸。

The purpose of this study was to establish appropriate and precise methods to evaluate the strength and the toughness of silicon nitride ceramics at room and high temperatures. The study was performed in two years from 1986 to 1987, in the Faculty of Science and Engineering, Ritsumeikan University.In 1986, testing equipments to evaluate the strength under monotonic tensile and three points bending load conditions were designed and fablicated. An attension was paid to obtain a precise allignment of the load transmission path in each case. Systematic experiments were conducted at room and high temperatures up to 1300 C on a number of silicon nitride ceramic specimens y using the developed loading equipments. Results obtained through the tests were analized statistically, and the following two points were mainly discussed; (1)temperature dependence of Weibull parameters, and (2) statistical propertirs of the strength under monotonic tensile and three points bending load conditions.In 1987, the experiments were carried out continuing to the previous year, and the results obtained in two years were summarized and discussed to establish the methods of how to evaluate the strength and the toughness of silicon nitride ceramics at room and high temperatures. The obtained results in addition to the above are as follows: (3) The strengthes under two types of load conditions can be well correlated when the effective volume concept is taken into account, (4) the fracture toughness at high temperature takes the same value as that at room temperature when a crack length increment due to slow crack growth is considered at high temperature, and (5) the liner fracture mechanics concept seems to be applicable to the fracture criterion even for small size inherent defects existing in silicon nitride, when the size of segregated Fe area around the fraxture origin is considered as the defect size.