Processing and performance of ultra high temperature ceramic matrix composite (UHTCMCs) using radio frequency assisted chemical vapour infiltration (RF-CVI)

Ultra-high temperature ceramic matrix composites (UHTCMCs) have been produced using a radio frequency assisted chemical vapour infiltration (RF-CVI) process. The composites were based on 2.5D carbon fibre preforms with a 0 / 90° (out of plane) fibre orientation and containing 23 % fibre volume fraction. These were initially impregnated with zirconium diboride (ZrB₂) powder in the form of a slurry and then, after solvent removal, the majority of the porosity filled with pyrolytic carbon (PyC) using the RF-CVI process at 1273 K and 0.5 kPa chamber pressure. The latter resulted in a uniform rough laminar texture with good interfacial bonding. As intended, an inverse temperature profile was achieved using the RF heating, enabling uniform densification of the preform from the inside out, with no entrapped porosity and achieving 90 % of theoretical density in only 24 h, at least a tenfold reduction in processing time compared to the conventional CVI process and a fivefold reduction compared to other modified CVI processes such as forced flow or pressure gradient CVI. The resulting UHTCMCs displayed good mechanical strength and thermo-ablative behaviour.