GE to mass-produce CMCs for the first time

Engineers like GE Aviation’s Sanjay Correa believe that “we’re running out of headroom in metals.” He and his team at GE say that a new class of materials called ceramic matrix composites (CMCs) is set to revolutionise everything from power generation to aviation, and allow engineers to build more powerful and efficient jet engines before the end of the decade.

Correa leads GE Aviation’s CMC programme and the company has announced that it will spend $200million to build two new CMC factories in Huntsville, Alabama.

The Rocket City factories - a nickname tied to Huntsville’s role in launching astronauts into space – will be supplying raw material to the first American CMC plant, which GE opened last year in Asheville, North Carolina. The company already operates two CMC ‘lean labs’ in Newark, Delaware, and Cincinnati, Ohio, that are looking for new applications for the materials and new ways to make them.

“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,” Correa said.

GE scientists have been working on CMCs for two decades. These ‘super ceramics’ are as tough as metals, but they are also two-thirds lighter and can operate at 1316°C - 260 degrees higher than the most advanced alloys. This combination allows engineers to design lighter components for engines that don’t need as much cooling air, generate more power and burn less fuel.

Correa and his team believe that CMCs could allow designers to increase jet engine thrust by 25% and decrease fuel consumption by 10% by 2020. While these numbers promise great things, CMCs have been extremely difficult to mass-produce. Until recently, their use was limited to the space industry and fighter jet exhaust systems.

In 2000, GE’s Oil & Gas business tested CMCs inside a 2MW gas turbine in Florence, Italy. By the middle of the decade, turbines with CMC shrouds were running for thousands of hours without a hitch.

GE’s aviation business picked up the technology in 2007 and started looking for jet engine applications at its lean laboratory in Delaware. GE Aviation first used the material for CMC shrouds in its F136 fighter jet engine, but their application quickly spread. Static CMC parts are already flying inside the next-generation Snecma (Safran) engines.

In 2015, GE started testing CMC components in a GEnx engine – the type used by many Boeing Dreamliners – to mature the technology for its latest large engine: the GE9X. When finished, the GE9X will be the largest jet engine ever built with an 11 foot fan diameter capable of producing 60:1 air compression.

Earlier this year Correa’s team 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 will produce 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.

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 ecosystem – the lean labs in Ohio and Delaware – are already looking for new applications for the materials and new fabrication methods, respectively.

Author
Tom Austin-Morgan

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