CHEMICAL VAPOUR INFILTRATION (CVI) OF SILICON CARBIDE FIBRE PREFORMS

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

Computed Tomography as a Tool for Examining Surface Integrity in Drilled Holes in CFRP Composites

In light weight structures the joining of composite materials and of composites to metals are key technologies. A manufacturing method associated with joining is the drilling of holes. The hole creation in CRFP through drilling is associated with several defects related to the process, both on the entry and exit sides of the hole and also with dimensional and surface roughness issues of the hole wall. The detection of damage due to the process is not trivial. Especially interesting is non-destructive methods. In this work X-ray computed tomography is used to determine defects due to drilling of holes in a CFRP composite using twist drills with different geometrical features at different drilling parameters. The results can be used to establish relationship between different geometrical features of drills in combination with cutting parameters and resulting surface integrity of holes