CHEMICAL VAPOUR INFILTRATION (CVI) OF SILICON CARBIDE FIBRE PREFORMS

Abstract
An alternative fabrication technique is proposed for ceramic matrix / ceramic fibre composites involving filling a fibre fabric preform with a Si/Si₃ N₄ slurry and subsequently reaction bonding. For the first processing step in this process, chemical vapour infiltration (CVI) was evaluated as a means of both biding together and protecting the fibres. SiC (Nicalon) fibre preforms consisting of through-stitched 2D fabrics were infiltrated. The preform thickness was more than 4 mm and a 3 µm TiC/TiN layer was subsequently deposited on all the fibres, even in the centre of the preform after less than 8 h. The purpose of the CVI layer was firstly to bind the fibres together, but also to protect the fibre/matrix interfacial carbon film from reaction with the subsequently infiltrated matrix. The remaining porosity of the preform was filled with a Si/Si₃ N₄ powder slurry which was nitrided to form a reaction bonded Si₃ N₄ (RBSN) matrix. The advantage of this combined CVI/RBSN route is a substantial cut in processing time compared to a process where most of the porosity is filled using CVI.