There are many applications, particularly in the aerospace and automobile industries, that require composites with a high temperature resistance. Metal, glass and ceramic-matrix composites provided higher temperature resistance with operating temperatures up to 900° C.
There are many applications, particularly in the aerospace and automobile industries, that require composites with a high temperature resistance. For that reason, it is important to develop new processes that can produce composites with high operating temperatures.
Metal Matrix Composites (MMC)
In composites where the matrix is composed of a metal (metal matrix composites, or MMCs) it is possible to produce a material with a higher temperature resistance than more common plastic-based composites. The reinforcement fibers in this type of composite are usually composed of boron, graphite, or silicon carbide (SiC). MMCs can generally provide operating temperatures up to 500° C.
Glass or Ceramic Matrix Composites (CMC)
To achieve even higher operating temperatures, the matrix and/or the reinforcement fibers can be composed of glass or ceramic (CMC). Alternatively, the matrix of a carbon/graphite composite can be carbonized. This process produces carbon-carbon composites which are often used for brake disks in airplanes or Formula 1 race cars. The operating temperatures for this class of materials can reach 900° C or higher.
NASA formed the Ultra-Efficient Engine Technology program in 1999 to develop new technologies for superior turbine engines. One of the program’s projects, Materials and Structures for High Performance, is focused on developing advanced high-temperature materials for use in propulsion systems. Hyper-Therm High Temperature Composites, Inc. (Hyper-Therm HTC) partnered with NASA and the UEET program to produce an actively cooled, continuous fiber-reinforced silicon carbide matrix composite for liquid rocket propulsion systems — the world’s first.
Hyper-Therm’s innovative composites use isothermal/isobaric and forced-flow chemical vapor infiltration (CVI) processes for production. In terms of composition, Hyper-Therm’s most popular high-temperature materials have carbon and silicon carbide reinforcing fibers in a CVI silicon carbide matrix. The fibers can then be further coated with boron nitride doped with silicon, pyrolytic boron nitride, or pyrolytic carbon (PyC) to optimize strength, fracture toughness, and strain-to-failure. When applications require higher durability in potentially corrosive environments, Hyper-Therm’s multilayer silicon carbide fiber coating and pseudo-porous silicon carbide systems can be used. The multilayer fiber coating uses weakly bonded layers (about 100 nanometers thick) of silicon carbide to reduce the problems of oxidation and moisture corrosion that reduce the performance of PyC and boron nitride fiber coatings. In contrast, the pseudo-porous fiber coating system uses a breakable monolayer (less than 1 micrometer) network of porous silicon carbide and was also developed to combat the oxidation and moisture problems associated with PyC and boron nitride.
New high temperature materials are being developed every day. In the future, it is very possible that we will see composites with operating temperatures that are much higher than 900 deg. C, allowing for ever lighter and more temperature resistant materials.