Researchers at HRL Laboratories ((Malibu, CA) report that achieved a new milestone in 3D printing technology by demonstrating an approach to additively manufacture ceramics that reportedly overcomes the limits of traditional ceramic processing and enables high temperature, high strength ceramic components.
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.
“We use a UV-curable siloxane resin system that was formulated by mixing mercaptopropyl-methylsiloxane with vinylmethoxysiloxane and adding UV free-radical photo initiator, free-radical inhibitor, and UV absorber,” explains Tobias A. Schaedler, Senior Scientist, Architected Materials, at HRL’s Sensors and Materials Laboratory.
HRL has demonstrated use of the material with two different additive manufacturing methods: With conventional stereolithography using commercially available printers from vendors such as the Formlabs or Viper, the process is time-consuming and it takes about 4-8 hours to print a 1-2-inch tall structure according to Schaedler. “The width and length are limited by the build platform of the printer, typically ~10″ x 10.”
With the self-propagating polymer waveguide (SPPW) process developed at HRL, however, the process is much faster. This process irradiates UV light onto a vat filled with the resin that is covered with a patterned mask. Holes in the mask expose the resin with UV light, which cures the resin. On curing/polymerization there is a slight change in the index of refraction that traps the light in the polymer. “Using this ‘trick,’ a waveguide can be ‘grown’ by continued exposure,” says Schaedler, “thereby forming straight struts of polymer in the liquid resin. While the process is more rapid, a 0.5-1-inch-thick structure can be formed with an area of 10″ x 10” in just 30-60 seconds, the possible shapes are limited to linear extensions of the pattern in the mask, i.e., lattices or honeycombs, for example.
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 Schaedler. “Comparing 3D printed microlattices to ceramic foams of similar density we have measured a 10 times higher compressive strength.”
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.
HRL Laboratories 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 provides custom research and development and performs additional R&D contract services for its member companies, the U.S. government, and other companies.