Image Credit: grc.nasa.gov
Ceramic matrix composites (CMC) consist of ceramic fibers reinforced with particulates, fibers, or cloth. Compared to conventional technical ceramics, which fracture easily under loads, CMCs have a greater crack resistance. Some matrices and combinations also provide greater strength, thermal shock stability, and erosion resistance at very high temperatures.
How CMCs are Made
Ceramic matrix composites are fabricated through vapor phase infiltration or deposition techniques. These methods include chemical vapor infiltration (CVI), liquid phase infiltration (LVI), and melt infiltration (MI). Chemical vapor infiltration (CVI), a variant of chemical vapor deposition (CVD), is used to fabricate alumina-alumina CMCs. Liquid phase infiltration (LVI) is used to densify powder-metal skeletons. Advanced ceramics produced with melt infiltration (MI) or reactive melt infiltration (RMI) is also available. With RMI, the liquid or vapor phase reacts to form a new phase or ceramic material.
Whisker, particle, or continuous fiber reinforcements are used to overcome the brittle nature of conventional ceramic materials. The resulting ceramic matrix composites provide toughness and strength at high temperatures. Stiffer or higher modulus fibers, particles, or cloth can be used to reinforce or strengthen a lower-modulus ceramic matrix. These high modulus reinforcements bear the load well and produce a higher-strength material. A good interface or interphase coating between the reinforcement and matrix is required to achieve load transfer and desired performance. If the reinforcement is too tightly bound to the matrix, however, ceramic matrix composites may exhibit lower toughness.
Ceramic matrix composites (CMC) differ in terms of reinforcement materials. Carbon fiber reinforced carbon matrixes or silicon carbide fiber reinforced silicon carbide matrixes provide a tougher material for high temperature and ballistic applications. In addition to carbon or carbon fiber, choices include silicon carbide (SiC), silicon platelets, tungsten particles, chromium particles, alumina fibers, silicides, and aluminides. Ceramic matrix composites may also feature matrices with zirconium carbide, hafnium carbine, tantalum carbide, alumina, zirconia, and glass ceramics. Suppliers of ceramic matrix composites are able to assist with the selection of the proper particulate, fiber, or cloth reinforcement materials.
Applications for Ceramic Matrix Composites
Ceramic matrix composites (CMC) are used in materials applications that require high strength, high temperature resistance, armor or ballistic properties, and erosion or wear resistance. In addition to jet engines and rocket engines, ceramic matrix composites are used in internal combustion engines for automobiles, gas turbines, process equipment, furnaces, refractory components, nuclear components, spacecraft re-entry shielding, welding nozzles and tools, and brazing fixtures. Ceramic matrix composites are also used in the replacement of superalloys.