Ceramic composites eye applications

The development of silicon carbide matrix composites is giving rise to host of initial applications in the aerospace industry and beyond. For example, General Electric (GE) is to ‘mass-produce’ ceramic matrix composites (CMC), following an announcement that the company will build two CMC factories in Alabama at a cost of $200million.

GE makes CMCs from silicon carbine fibres embedded in a silicon carbide matrix. The fibres are five times thinner than human hair and coated with a highly proprietary coating, said to result in a material that is tough like a metal but not brittle like a ceramic. The other two components of GE’s CMC ecosystemare already looking for new applications for the materials and new fabrication methods, respectively.

GE has long been developing the materials and says they have reached a point where they are suitable for wider roll out in the company’s range of turbine engines used by aircraft and power generation.

The ‘super ceramics’ are as tough as metals, but they are also two-thirds lighter and can operate at temperatures as high as 1316°C – allowing the potential for greater thermal efficiencies, generating more power and burning less fuel. They will also allow engineers to design lighter components for engines that don’t need as much cooling air.

GE believes that CMCs could allow designers to increase jet engine thrust by 25% and decrease fuel consumption by 10% by 2020.

The company already operates two CMC ‘lean labs’ in Delaware and Ohio that are looking for applications for the materials and new ways to make them.

Dr Sanjay Correa is vice president for CMC Programs at GE Aviation, says: “We’re running out of headroom in metals.

“Opening the new plants in Alabama is a key step in building up the supply chain we need to make CMC parts in large volumes,”

CMCs have, to date, been extremely difficult to mass-produce. Until recently, their use was limited to the space industry and fighter jet exhaust systems. GE’s aviation business picked up the technology in 2007 and started looking for more mainstream jet engine applications.

Static CMC parts are already flying inside the next-generation Snecma (Safran) engines, and in 2015 GE started testing CMC components in a GEnx engine – the type used by many Boeing Dreamliners. It wants to use the material on large fan and compressor blades on it GE9X currently in development. When released to the open market, it will be the largest commercial jet engine ever produced with an 3.4m fan diameter capable of producing 60:1 air compression.

Earlier this year GE tested the first spinning parts inside the latest-generation ADVENT adaptive cycle engine, a demonstrator engine for the US Department of Defence. GE researchers have now started replacing rotating metal components with CMCs.

Shedding the weight of these parts by two thirds produces a knock-on effect by lowering the centrifugal force inside the engine. This will allow designers to reduce the size of the engine’s main shaft and cut engine weight further.

Author
Tom Austin-Morgan

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