Ultra High Temperature Ceramics

Ultra High Temperature Ceramics (UHTCs) are good choices for several extreme applications: thermal protection materials on hypersonic aerospace vehicles or re-usable atmospheric re-entry vehicles, specific components for propulsion, furnace elements, refractory crucibles, etc. This family of ceramic compounds is made of borides, carbides and nitrides such as ZrB2, HfB2, ZrC, HfC, TaC, HfN which are characterized by high melting points (table 1), high hardness, chemical inertness and relatively good resistance to oxidation in severe environments.

Historically, this family of ceramic materials was first investigated between the 1950s and 1970s by Russian and U.S. laboratories but recent studies to develop hypersonic flight vehicles in particular have led to a resurgence of interest. For hypersonic vehicles with sharp aerosurfaces (engine cowl inlets, wing leading edges and nosecaps), there are foreseeable needs for materials that can withstand temperatures of 2000 to 2400°C, operate in air and be re-usable . At present, the structural materials for use in high temperature oxidizing environments are limited to SiC and Si3N4 based materials, oxide ceramics and C/C composites with thermal protection. Silicon-based ceramics and protected C/C composites exhibit good oxidation resistance, but only up to ~1600°C, and their thermal cycling lifetimes are modest. The development of structural materials for use in oxidizing and rapid heating environments at temperatures above 1600°C is therefore of great importance for engineering.

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