Impregnation Molding of Particle Filled Preceramic Polymers into Fiber Preforms

Abstract

Development of preceramic polymers has enabled the use of traditional polymer processing techniques, such as resin transfer molding (RTM) for the processing of ceramic-ceramic composites where continuous-fiber ceramic preforms are impregnated using PCP's and then pyrolized to convert the matrix into ceramic. One of the issues in this process is the void formation due to densification of the PCP's and the mass loss during pyrolysis. An effective way of reducing voids and shrinkage is to use suspensions of filler particles for the matrix material. The filler particle distribution during the infiltration of fiber preforms with particle-filled preceramic polymers has a crucial effect on the degree of cure and the properties of the finished product. The filler particles are also expected to reduce microcracking during the service of the ceramic composite. This paper constitutes the first phase of a comprehensive study to investigate the mechanics of particle filtration during the impregnation process and to establish the correlations between various processing parameters. A two-dimensional numerical filtration model is developed to predict the volume fraction distribution of the filler particles during the impregnation process. The non-linear relations between the filler particle distributions, the flow properties and the mold geometry are also investigated.