Radio frequency-assisted zirconium carbide matrix deposition for continuous fiber-reinforced ultra high temperature ceramic matrix composites

Zirconium carbide (ZrC) is considered to be a potential candidate for ultra high temperature applications due to its high melting point, good chemical inertness, and ablation resistance, but the monolithic form suffers from low fracture toughness and hence poor thermal shock resistance. Reinforcing it using continuous carbon fibers (C_f) to create an ultra high temperature ceramic matrix composite is an obvious solution, however densifying ZrC requires the use of very high temperatures combined with significant pressure, such as obtained by using hot pressing or spark plasma sintering, which risks damaging fibers. In the present work, radio frequency-assisted chemical vapor infiltration (RF-CVI) has been investigated with a view to forming C_f/ZrC composites. These initial experiments revealed the ability to deposit pure, nano-grained, and near stoichiometric ZrC with deposition occurring preferentially from the center of the sample due to the nature of the inverse temperature profile developed. The deposited ZrC grains were in the range of 4–9 nm in size and had a lattice parameter of 0.4750 nm. The work also showed that the use of RF-CVI enabled the minimization of early pore sealing, a common problem for conventional CVI.