“Stronger” than a speeding bullet
Ceramic materials are well known for their ability to withstand very high temperatures, which makes them highly desirable for use as structural materials in systems that utilize very high temperatures, such as gas turbine engines. Use of ceramic turbine components would significantly increase the efficiency of those engines. For instance, in large industrial gas turbine engines, such as those used for electric power generation, the energy efficiency could be increased by about one percentage point, which would correspond to a savings of over two million dollars per year in fuel cost savings and reduced emissions of over 6,000 metric tons of CO2 in a typical combined cycle plant. The engine performance improvements can be even greater for aviation engines where both the higher temperature capability and lower density of ceramics can be used to advantage.Unfortunately ceramics are also well known for their tendency to fail in a brittle, catastrophic fashion (think window glass or china dinnerware). However, GE scientists at GE Global Research, GE Aviation and GE Energy have been working to develop ceramic matrix composite (CMC) materials that combine the high temperature resistance of ceramics with the mechanical toughness normally associated with metals.
One technique for measuring a material’s relative toughness is ballistic impact testing, or “shooting it with a bullet”. Recently such testing was performed through our partnership with the U.S. Department of Energy. Even relatively high strength ceramics, such as silicon carbide or silicon nitride, fail catastrophically in such ballistic tests. The following video shows the result of firing a steel ball projectile into a silicon carbide plate at >150mph.
GE researchers have used this same basic ceramic, silicon carbide, to develop a strong and tough ceramic composite material. Silicon carbide fibers, roughly 1/6th the diameter of a human hair, are used to reinforce a silicon carbide matrix. Careful engineering of the bonding between the fibers and matrix yields a CMC material that is many times tougher than traditional ceramics. In fact, the composite is tough enough to withstand the same ballistic impact conditions without failure.
GE’s ceramic matrix composites are able to operate at temperatures exceeding 2,000°F, well above the capability of current nickel alloys typically used as high temperature structural materials in gas turbines. The ceramic composite is also 1/3 the density of nickel, giving a significant weight advantage for aviation applications. As the world’s leading manufacturer of gas turbine engines for both aviation and power generation applications, we at GE are excited about the potential this new ceramic matrix composite holds for increasing the efficiency and power output of such engines while simultaneously reducing emissions. In fact, we believe GE’s ceramic matrix composites are going to redefine what is possible in the world of aviation and energy.
Over the past several years, the process for making this CMC has been transitioned from GE Global Research to GE Ceramic Composite Products, LLC, GE’s production facility in Newark Delaware, where it is manufactured under the HiPerComp® name. GE is also actively developing and testing several types of turbine components made of CMC. GE Energy has field -tested CMC shrouds in a 7FA engine (170 MW simple cycle) for over 5000 hours. A GE CMC combustor liner has also run for >12,000 hours in a 5 MW Solar Turbines engine. GE Aviation has run a CMC combustor liner and CMC blades in a government demonstrator engine. CMC low-pressure turbine vanes are being used in the GE – Rolls Royce F136 development engine for the Joint Strike Fighter. Flight-testing of this engine will begin in 2010, and this CMC vane could be the first production application of HiPerComp®.