The aim of the project was to develop new advanced Ultra High-Temperature Ceramic Matrix Composites (UHTCMCs) with significantly improved high temperature mechanical properties for aerospace applications, such as thermal protection system for hypersonic and atmospheric re-entry vehicles, and parts of propulsion systems. A successful operation of reusable hypersonic vehicles relies on Thermal Protection System (TPS), which is a barrier that shields the heat produced by the friction of atmospheric gasses against the outer surface of a space vehicle. Advanced space systems require materials capable of prolonged operations in oxidizing atmospheres above 2000°C, for example the maximum operating temperature for TPS of hypersonic vehicles is expected to exceed 2200°C, but the combustion temperature of a scramjet propulsion system reaches 2700°C. Therefore, it was the main objective of the project to offer a solution for the preparation of new advanced ceramic materials that would meet such strict requirements of aerospace industry.
To fulfil the aim of the project, the effect of various types (Eu2O3, Yb2O3, Lu2O3) and amounts (2, 5, 10 wt.%) of rare-earth (RE) oxides on the densification, microstructure and phase evolution, as well as mechanical properties of transition metal diboride ceramics (ZrB2-SiC) was investigated. The addition of 5 wt.% Lu2O3 was selected as the most promising additive, based on the excellent combination of room and high temperature properties of the materials. The project was then focused on the development of innovative processing way to incorporate ZrB2-SiC- Lu2O3 and HfB2-SiC-Lu2O3 into the carbon fibres-reinforced silicon carbide (Cf/SiC) composites. This relied on the incorporation of B4C powder into the Cf/SiC matrix, followed up by the deposition of the slurry containing either HfSi2+Lu2O3 or ZrSi2+Lu2O3 onto the Cf/SiC surface. Above the melting temperatures of disilicides, the melt infiltrated into the composites by capillary forces, where reacted with B4C and carbon fibres to form HfSi2/SiC/ZrC or ZrSi2/SiC/ZrC compositions. The desired composition was obtained in the subsurface layer (up to ~ 1 mm) of the Cf/SiC, but also in the form of a continuous outer layer on the surface. The Lu2O3 did not infiltrate into the composite matrix, but stayed homogenously distributed in the outer layer. The obtained knowledge was successfully transferred to the industrial partner Central R&T (CRT) Airbus Defence and Space.
