The creation of "new" ultra high temperature ceramic matrix composites using the "old" sintering methods of bulk ceramics

UHTCMCs represent a novel class of materials, which can potentially couple the high oxidation resistance of UHTCs to the damage tolerance of CMCs, provided that a suitable matrix/fiber interface is tailored. Their specific application is in hypersonics and propulsion. Current technologies for UHTCMC manufacturing originate from consolidated technologies for CMCs, such as chemical vapor infiltration (CVI), polymer infiltration and pyrolysis (PIP), reactive metal infiltration (RMI). The adaptation of these techniques to obtain a UHTC matrix is not easy, for several reasons. For instance, there are no commercially available polymeric precursors of UHTC phases, to be used for PIP. Infiltration with reactive alloys containing borides poses major problems of wettability and residues of metal in the final composite. In this talk, we explore the manufacturing of UHT-Composites via slurry infiltration followed by hot pressing. Several kinds of composites have been produced using different preforms, continuous and discontinuous fibres, different textures and architectures. As for the sintering of bulk ceramics, we show that an appropriate choice of doping elements is of fundamental importance for a successful densification. Even more, the choice of sintering aids affects not only the nature of fiber/matrix interface, but also the high temperature behavior of the materials. Recently, hot pressed UHTCMCs have been tested in relevant environment showing an excellent ablation and erosion resistance up to temperatures of 2500-3000°C.