Sharp UHTC leading edges composites for hypersonic applications

Hypersonic vehicles need sharp leading edges to enable vehicle manoeuvrability during atmospheric exit and re-entry. The edges are expected being hit with corrosive plasmas from atmosphere at ablative speeds with temperatures inexcess of 2000°C. Such extreme conditions limit the field of material candidates to ultra-high temperature ceramics (UHTCs). These are typically non-oxides with melting/decomposition temperatures in excess of 3000°C: borides of the group IV transition metals like ZrB2 and HfB2 are currently the most studied systems. Bulk single-phase UHTCs for these high-temperature structural applications are limited by their poor oxidation resistance, as well as lacking damage tolerance. Recent development of composite UHTC systems has focused on additions of SiC in form of fiber in order to improve not only resistance to oxidation but also resistance to thermal shock. In the present contribution, leading edges with a sharp profile were produced in the system MB2-SiC fibers, M= Zr and Hf. The dynamic response to oxidation was studied under aero-thermal heating using a supersonic flow (enthalpy up to xx MJ/kg aggiungi quanto serve) using a arc-jet plasma gallery. Temperature and surface emissivity were on-line monitored. Microstructural modifications upon oxidation were analyzed and correlated to test conditions through Computational Fluid Dynamics simulations.