Ultra-high temperature CMC with self-healing capability

Materials for new generation space crafts have to satisfy a strict set of requirements due to the high thermo-mechanical loads to which they will be subjected during the various phases of the flight. Among these, zirconium diboride (ZrB2), belonging to the ultra-high temperature ceramic (UHTC) class, is one of the most refractory material possessing interesting engineering and physical properties. Although high mechanical strength can be achieved upon suitable microstructure design, low fracture toughness and critical oxidation resistance remain two of the most serious issues to solve. Strategies to solve these limitations include the addition of fibers, that render the composite more failure tolerant, and Si-containing phases, able to form silica glass that seal the oxidation defects during service at high temperatures. Currently, ISTEC is trying to design and manufacture a new class of out-performing, Ultra-High Temperature Ceramic Matrix Composites (UHTCMCs) based on C or SiC fibres/preforms enriched with ultra-refractory ceramics capable of in-situ repairing damage induced during operation in severe aerospace environments. In this work, composites based on ZrB2 and containing chopped or continuous fibers from 5 to 50 vol% are presented. The self-healing capability of doped and undoped composites is discussed.