Ceramic matrix composites (CMCs) can offer multiple advantages for a range of high-tech industries, such as aerospace, defense and automotive. Attendees of Ceramics Expo 2016, which will be held April 26-28 in Cleveland, Ohio, will have the opportunity to learn about those benefits, as well as the current state of the manufacturing environment for this exciting technology. I recently had the opportunity to discuss CMCs with several of the industry leaders who will be giving presentations during the “Developing the Supply Chain for Ceramic Matrix Composites” track on Tuesday, April 26, from 11:45 a.m.-1:15 p.m.

How has CMC technology evolved?

Doug Freitag: Ceramic matrix composites have been under development for the last 30 years. In the last five years, we’ve seen a significant turn of events in that they’re really becoming commercial. Ceramic matrix composites are now rapidly being adopted by the market, which is creating new supply chains (such as in processing equipment, raw materials, machining systems) that are continuing to evolve. People who might not have considered ceramic matrix composites in the past can really get a better understanding of what supply chains might be evolving and where the opportunities might be for their companies to participate.

What can attendees of the CMC track expect to hear?

Freitag: Speakers will discuss ceramic matrix composites manufacturing issues, as well as what some of the remaining gaps are. We’ve got three representatives who are developing ceramic composite or advanced ceramics for gas turbine applications, and one who will be talking about commercial applications in development for ceramic composites in pumps used in harsh environments.

How are CMCs produced?

Robert Cook: CMCs can be produced via four primary methods: polymer infusion and pyrolysis, melt infiltration, chemical vapor infiltration, or 3-D printing. Lancer focuses on polymer infusion and pyrolysis (PIP)-processed components due to the comparatively lower production costs and higher levels of customization of the final product.

Via the PIP process, the component is initially processed near-net shape as a polymer composite using conventional thermoset polymer processing methods. This pre-ceramic polymer matrix is comprised of chemistry such that, when pyrolyzed at high temperature (and in an inert atmosphere), it transitions from a polymer to a porous ceramic. This porous ceramic is then repeatedly infiltrated under vacuum with additional pre-ceramic polymer and repyrolyzed until a desired density level is achieved. Once the component has achieved its required density, the composite is machined to its required dimensions.

What benefits can CMCs offer over traditional materials (e.g., metals, polymers)?

Cook: CMCs provide all of the benefits of conventional monolithic ceramics, but with the added benefit of thermal and mechanical shatter resistance. Compared to polymers, select improvements include the ability to handle much higher working temperatures (1,400°C and higher), chemical inertness and high abrasion/wear resistance. Compared to metals, CMCs again offer higher working temperatures and great wear resistance, but more importantly, they offer increased dimensional stability and a three- to five-time decrease in weight. In both cases, it can be boiled down to hotter, faster and lighter—with a longer life.

How can design engineers determine if a CMC might be a good fit for their application?

Cook: The best way is to have a discussion with experts in the field of CMCs. Education into current CMC properties, uses and production methods will allow engineers to vet if the material makes sense for their application. Production costs associated with CMCs have dropped by an order of magnitude in the past 30 years, increasing the availability and usefulness of this novel family of materials dramatically in the aerospace, defense, automotive, semiconductor, and industrial rotating equipment sectors. 

How can CMCs be tailored to specific applications?

Cook: CMCs generally consist of three components: a ceramic matrix, a reinforcing fiber and property-modifying refractory filler particles. Different types and combinations of matrices, fibers, and fillers result in different composite surface and bulk properties. In addition, processing conditions can be modified to control the overall molecular structure of the ceramic matrix, resulting in controllable mechanical, electrical, thermal, tribological and chemical performance. Finally, density and porosity can be modified to control permeability through the composite.

How does Rolls-Royce use ceramic matrix composites?

Jay E. Lane: Rolls-Royce makes aero engines, and we’re interested in CMCs to replace nickel-based superalloys in the turbine engine. [CMCs are preferred in this application because] they have higher temperature capability than nickel-based superalloys. Because we can use them at higher temperatures, that means we need less cooling air than you would for a metal. If you use less cooling air, you can basically improve your specific fuel consumption (or get better gas mileage if you want to think of it that way).

CMCs are also lower density (by about one-third), so that means we can save weight. With aircraft, whenever you can save weight, you can save fuel. The savings can also be translated to increasing the range of the aircraft. In other words, I can go farther on the same amount of fuel because my plane weighs less.

What types of CMCs are you working with?

Lane: We’re trying to develop a CMC material that meets certain engine requirements. For the applications we’re looking at, it’s silicon carbide fiber, reinforced silicon carbide matrix CMC. These materials have the best set of properties and the best potential capability for these types of applications.

We’re also interested in oxide-oxide CMCs. Boeing did some testing on oxide CMCs where they made a tail cone and a nozzle out of oxide CMC and tested them on a Rolls-Royce engine. Going forward, we have our own interest in considering oxide CMCs for replacing either standard nickel-based alloys and/or titanium in low- to moderate-temperature applications. Whether it’s a mixer nozzle or a tail cone on the back of a smaller engine, for example, where we might traditionally use titanium or nickel-based alloys, the oxide CMC can provide both weight benefits and performance benefits.

USACA in Action

The U.S. Advanced Ceramics Association(USACA) supports the advanced ceramics industry through a variety of activities, including the development and updating of technical roadmaps that help show the federal government, academia and industry where the gaps are in specific technologies. Roadmap topics to date have included advanced monolithic ceramics, CMCs and transparent armor.

USACA is currently working on a roadmap focused on electromagnetic (EM) sensor windows, which are radio frequency (RF),electro-optical (EO) and infrared (IR)-transparent windows that are used on missile domes and aircraft. “Our interest in this area is that these sensor windows are used in very harsh environments, so traditional ceramic materials no longer will work in these applications,” says Doug Freitag, USACA’s technical director. “For example, in hypersonic applications with very high speeds, you see particle erosion and impact. Another application is very large windows that might be used on aircraft.”

Freitag will provide some details regarding the EM sensor window roadmap at Ceramics Expo. “We’ll be talking about the gaps for machining these windows, being able to make curved windows that are large, being able to make the materials that are of high enough purity to not have any interference when looking through them with various sensor systems,” he says. “We’ll also be talking about the U.S. capability in this area and our dependence on foreign sources of supply for the materials.”

USACA also helps support the advanced ceramics industry by hosting and participating in many industry events. Every year, approximately 300 attendees meet at the association’s Annual Conference on Composites, Materials, and Structures in Cocoa Beach, Fla., to attend ITAR-restricted technical sessions, walk the show floor, and network with their peers. When invited, USACA also attends meetings and provides updates to the federal government’s Interagency Coordinating Committee on Ceramic Research and Development (ICCCRD), where representatives from agencies such as the Department of Defense, NASA, Department of Commerce, and the Department of Energy meet to discuss what they’re working on in terms of ceramic materials development projects.

“We also take our information to Congress,” says Freitag. “We try to educate Congress on advanced ceramics and what the issues are related to advanced ceramics, including the industrial base and technical issues, anything that they might consider related to policy, as well as federal government investment in this area.”

To learn more about USACA, visit www.advancedceramics.org.