January 03, 2016

Breakthrough for customizing heat resistant ceramics into complex shapes for jet engines, ion drives and many other applications

Researchers at HRL Laboratories, LLC, have achieved a new milestone in 3D printing technology by demonstrating an approach to additively manufacture ceramics that overcomes the limits of traditional ceramic processing and enables high temperature, high strength ceramic components.

The researchers began with a vat of resin containing silicon, carbon and oxygen. They shone a pattern of ultraviolet light beams onto this resin, causing it to harden where the light shone through it. In 30 to 60 seconds, an item 0.5 to 1 inches (1.27 to 2.54 centimeters) thick can form, with a lattice or honeycomb shape, Schaedler said. The researchers then heat these objects to convert the material into silicon oxycarbide ceramic. This new method is 100 to 1,000 times faster than previous 3D-ceramic-printing techniques, the researchers said. Furthermore, electron microscopy of the end products detected none of the porosity or surface cracks that normally weaken ceramics; indeed, these silicon carbide materials were 10 times stronger than commercially available ceramic foams of similar density, the scientists noted. Since ceramics are notoriously brittle, Schaedler said, "We are working to reinforce our ceramics with fibers." However, it will take some time before these ceramics reach the market, he said. "We are at the discovery phase. It will take at least five years for an application to be commercialized," Schaedler said.

HRL Laboratories, LLC, Malibu, California is a corporate research-and-development laboratory owned by The Boeing Company and General Motors specializing in research into sensors and materials, information and systems sciences, applied electromagnetics, and microelectronics.

HRL’s Senior Chemical Engineer Zak Eckel and Senior Chemist Dr. Chaoyin Zhou invented a resin formulation that can be 3D printed into parts of virtually any shape and size. The printed resin can then be fired, converting it into a high strength, fully dense ceramic. The resulting material can withstand ultrahigh temperatures in excess of 1700°C and exhibits strength ten times higher than similar materials.

Ceramics are much more difficult to process than polymers or metals because they cannot be cast or machined easily. Traditionally ceramic parts are consolidated from powders by sintering, which introduces porosity and limits both achievable shapes and final strength. "With our new 3D printing process we can take full advantage of the many desirable properties of this silicon oxycarbide ceramic, including high hardness, strength and temperature capability as well as resistance to abrasion and corrosion." says program manager Dr. Tobias Schaedler.

The novel process and material could be used in a wide range of applications from large components in jet engines and hypersonic vehicles to intricate parts in microelectromechanical systems and electronic device packaging.

A form of ceramic called alumina is being used in new ion propulsion drive, which uses electricity to heat gas and generate ions, according to Charlie Spahr, executive director of the American Ceramics Council.

“Ceramics are really good where you want to reduce wear and tear,” Spahr said.

The Pentagon’s research branch has been funding various projects to discover new ways to build lighter, stronger and more heat-resistant materials for aerospace and military applications.

"The method described in the new Science paper brings us closer to the goal of being able to 'engineer in' desired material properties that generally are not found together, such as strength and low density or low weight, and to craft these materials into complex shapes,” said Stefanie Tompkins, director of the Defense Science Office at the Defense Advanced Research Projects Agency (DARPA).

Figuring out how to make customized 3-D printed ceramic parts could also make a difference in gas-fired power plants, for example, or other types of gas engines, according to DARPA officials.

Science - Additive manufacturing of polymer-derived ceramics

The extremely high melting point of many ceramics adds challenges to additive manufacturing as compared with metals and polymers. Because ceramics cannot be cast or machined easily, three-dimensional (3D) printing enables a big leap in geometrical flexibility. We report preceramic monomers that are cured with ultraviolet light in a stereolithography 3D printer or through a patterned mask, forming 3D polymer structures that can have complex shape and cellular architecture. These polymer structures can be pyrolyzed to a ceramic with uniform shrinkage and virtually no porosity. Silicon oxycarbide microlattice and honeycomb cellular materials fabricated with this approach exhibit higher strength than ceramic foams of similar density. Additive manufacturing of such materials is of interest for propulsion components, thermal protection systems, porous burners, microelectromechanical systems, and electronic device packaging.

Printing ceramics into complex shapes

Some materials, such as thermoplastics and metals, are naturally suited to being 3D printed because the individual particles can be fused together by applying heat. In contrast, ceramics do not fuse together the same way. Eckel et al. developed a way to pattern specific preceramic monomers using either 3D printing or stereolithography into complex, curved, and porous shapes. Upon heating, they observed almost no shrinkage, and the formed parts showed exceptional thermal stability

10 pages of supplemental material

SOURCES - HRL Laboratories, Youtube, Science Journal, Discover Magazine, Live Science

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