Innovators at NASA's Glenn Research Center have developed a rapid processing method that produces stronger, tailored silicon carbide (SiC) tows and even heals damaged or otherwise low-quality fibers. Never before could poor-quality SiC fibers be healed and improved by this magnitude. This simple microwave process enables SiC tows and parts made from SiC fibers to be integrated in previously impossible applications while significantly saving costs.
Glenn's novel technique uses a microwave sintering furnace to reduce power requirements, processing temperatures (by as much as 1000 °C), processing times, and costs. Thus, it is easier to produce quality, high-strength SiC tows, as well as to increase the effective yield of usable SiC material. This breakthrough process stands ready to significantly increase the implementation of lightweight, high-performance SiC/SiC ceramic matrix composite (CMC) materials and SiC fibers in aeronautics, automotive, power generation, and countless other industries that operate in extreme environments.
SiC fiber tows and preform materials are commonly used as reinforcements in CMCs to make parts for use in harsh, high-temperature environments such as aircraft engines. These materials are desirable for numerous high-temperature applications because of their very low weight and outstanding thermo-chemical inertness; however, the multiple-step process using electric furnaces to produce these materials has numerous drawbacks: the process is very expensive ($10,000 to $25,000 per spool), involves high temperatures (greater than 2000 °C), requires high power (more than 700 watts), and produces much wasted material. Glenn innovators have discovered an efficient way to improve the quality and strength of SiC fiber tows using a unique microwave-furnace design that induces molecular heating.
Glenn's innovation relies on microwave sintering to convert a polymer to ceramic fibers/tows/yarns or to manipulate commercially available SiC fibers to increase strength and improve other qualities. Not only can higher-quality tows be produced but old, damaged, or otherwise unusable fibers can be improved and recycled, thereby saving significant costs by increasing yield. Even entire engine components can be placed in the furnace and restored. The desired results can be achieved in minutes rather than the usual hours or even days.
Glenn's low-temperature microwave process provides greater control with less power, while eliminating plasma generation and minimizing arcing events. Because this method also facilitates the shaping of the SiC fiber after initial processing, fabricating preforms with 2D or 3D architectures becomes simpler.