A study of compaction characteristics and properties after sintering of ceramic powders

本研究的主要目的是对陶瓷粉末进行三维压制，研究陶瓷粉末的特性，从而建立一般应力状态下的本构方程或压制准则。如果能够做到这一点，就可以根据压实标准来研究烧结后的性能。使用陶瓷粉末(Si3N4)进行了三维压实，并讨论了压实过程中的特点。在低应力范围内，陶瓷粉末表现出特殊的行为方式，即容易发生颗粒破碎、团聚断裂和颗粒重排等现象。得到了以下结果：(1)添加烧结助剂的粉末可以在较低的应力水平下压制成型；(2)压实判据由主应力空间中的部分椭球体给出。(3)判据中包含的参数的取值与粉末的特性密切相关。利用粉末的特征和本构方程，进行了等静压(CIP)的刚塑性有限元分析。压坯的形状和密度在压坯中的分布取决于粉末的特性，也取决于胶囊的强度。因此，烧结后的压坯将根据不同的特性提供不同的性能。这是陶瓷粉末压制过程中非常重要的一点。

The main objective of this study is to carry out three-dimensinal compaction of ceramic powders to investigate their characteristics and thereby to develop constitutive equations or compaction criteria for general stress state. If this could be done, the properties after sintering could be investigated in terms of the compaction criteria.The three-dimensional compaction was carried out using a ceramic powder (Si3N4), either with or without sintering additives and the characteristics in compaction were discussed. In a low stress range the ceramic powders are said to behave in particular manner, i.e. tapping of the powder particles, fracture of the agglomerates and rearranging of the particles are likely to occur. The following results were obtained.(1) The powder with sintering additives can be compacted in a lower stress level compared to that without additives.(2) The compaction criterion apperars to be given by part of ellipsoid in the principal stress space.(3) The values of the parameters which are included in the criterion are quite dependent on the characteristics of the powders. The relationship between the parameters and the characteristics should be further investigated.By employing the characteristics and the constitutive equations for the powders, the rigid-plastic finite element analysis of isostatic compaction (CIP) was carried out. The shape of the compacts and distribution of the density in the compacts depended on the characteristics of the powder and also on the strength of the capsule. The compacts after sintering will thus provide different properties depending on the characteristics. This is a very important point in compactin of ceramic powders.