Specialty Materials, Inc.
Ceramic Matrix Composites
In many respects, ceramic materials can be considered a design engineer's dream. Typical characteristics include high strength and stiffness, both at room and elevated temperatures in caustic atmospheres; light weight and abundant raw materials, high hardness, friction resistance, and high electrical resistivity. However, the one characteristic that can turns this dream product into a nightmare is the lack of durability. Simply put, ceramics are very brittle. Fixing this issue would result in significant increased use of ceramics for structural applications.
Improved processing can help to a limited extent. But the most effective way to solve this problem and dramatically reduce the chance of catastrophic failure is to add ceramic fibers to the ceramic, thus creating a ceramic matrix composite (CMC). Considerable development work has been done in this area going back to the 1970s and involving many companies and organizations. The work is much too comprehensive to list here, but the reader should have no problem finding references on the internet. By far, the bulk of the work has been done using small diameter yarns (about the same size as carbon fibers in the range of 10 to 15 microns in diameter), principally composed of silicon carbide. These include such fiber products as Nicalon, Tyranno, and Sylramic. Again, much can be found in the literature about the work done with these fibers.
NASA Glenn Research Center has done extensive and comprehensive work on CMCs over the past 30 years. The most critical determinant for the high-temperature thermo-structural performance of a ceramic matrix composite is its creep-rupture strength, which in turn is highly dependent upon the creep resistance of the fiber. NASA has found that the most rupture resistant fiber at high temperatures is the SCS Ultra manufactured by Specialty Materials, Inc (SMI).
While the use of SCS Ultra in complex-shaped ceramic matrix composite parts is more limited than tow-based fibers because of its large diameter and high stiffness, there is little doubt that this fiber can be widely used for high-temperature structural applications because its thermo-structural properties are superb. SMI has supplied Ultra SCS to several organizations, with the most extensive data being generated by Hyper-Therm HTC of Huntington Beach, CA. Some of the data from Hyper-Therm can be viewed by cliicking on the following tab: Hyper-Therm data
A recent article in High Performance Composites magazine discusses the emerging market for ceramic matrix composites.