Ultra-High temperature Ceramics

Written by Laura Silvestroni, Institute of Science and Technology for Ceramics (IT) and YCN committee member

Ultra-high temperature ceramics (UHTCs), including transition metal diborides and carbides, are characterized by melting temperatures exceeding 3000°C and a combination of engineering and physical properties that make them suitable candidate materials for thermal protection system (TPS), coatings for materials subjected to high temperatures, and components for sharp leading edges on hypersonic re-entry vehicles. 
Despite the high melting points of pure UHTCs, they are unsuitable for many refractory applications, because of their high susceptibility to oxidation. Additives and secondary phases can notably improve their capability to withstand oxidation damages.
Additionally, although some UHTCs demonstrated room temperature flexure strength up to 1GPa, a lack of damage tolerance typical of brittle ceramics still needs to be addressed. 
The development of oxidation resistant and tougher massive UHTC can be pursued through the achievement of a "composite inside a composite". Such a multi-scale architecture may provide damage tolerant and strong structural ceramics. Reinforced and ad-hoc doped composites should reduce the risk of catastrophic failure over current UHTC bulk systems. 

  Microstructure of a short fiber reinforced UHTC.