New 3-D Printing Technique Makes Tougher Ceramics
Ceramics are some of the hardest materials on Earth. They can withstand extreme temperatures, and some are impervious to friction, scratching, and other mechanical stresses that wear out metal and plastic. But it can be difficult to make complex shapes out of the materials.
Chemical engineer Zak Eckel and group leader Tobias Schaedler.
Chemists at HRL Laboratories in Malibu, California, may have gotten around that problem by developing ceramics that can be made in a 3-D printer. The result: ultrastrong objects that are impossible to make using conventional methods.
Ceramics are used today in brake pads, the housing of microelectronics, and thermal shielding tiles (like the ones on spacecraft). Now the scientists at HRL are trying to substantially expand the applications. If parts for aircraft engines were made of ceramic, for example, the engines could run at a higher temperature, increasing their efficiency.
Ceramics could also offer an upgrade on parts used in steam turbines and other machines that must withstand searing, mechanically harsh conditions. The lab is co-owned by Boeing and General Motors, and the project has some funding from DARPA, the R&D arm of the U.S. Department of Defense.
Left: This beaker of resin contains polymer precursors that can be run through a 3-D printer to make objects. Right: In the printer, ultraviolet light strikes the resin, hardening it to build things one layer at a time. After about 90 minutes of printing, this small part, an impeller, emerges from the resin bath. Impellers are used in steam turbines and other machinery that must weather wear and high temperatures. Left: The printed part is treated in a furnace to bake the polymer and turn it into a ceramic. In the process, the part shrinks by about 30 percent. Right: Schaedler gets ready to pull the ceramic part out of the 1,000 °C furnace. To test the material’s heat tolerance, HRL scientists put it under a torch of about 1,200 °C.
HRL’s trick is to formulate special resins that can be used as the ink in a printer. They are made out of polymers but carry in their molecular structure silicon and other elements found in ceramics. These resins are loaded into 3-D printers to make parts with baroque shapes, such as corkscrews and sheets of intricate lattices. Then those parts go into a furnace to bake out the organic polymer components, leaving behind ceramic material.
Larger pieces of printed ceramic mesh and lattice sheets like these could be used to shield spacecraft from extreme temperatures.
The 3-D-printed ceramics could be better in some respects than their conventional counterparts. One lattice made at HRL has 10 times the compressive strength of commercially available ceramics. These printed parts can also tolerate heats as high as 1,700 °C, a temperature at which other ceramics start to degrade.
But the group still hopes to make its printed ceramics stronger. One approach is to design new kinds of pre-ceramic polymers that have fibers embedded in them to stop cracks from spreading. Ceramics are brittle and can fail catastrophically with one crack. It wouldn’t do if a minuscule defect caused a clever new part to shatter.