sound familiar to those who work with carbon composites. “We put the fi ber through a slurry compound that has all of the matrix constituents in it, including carbon, silicon carbide. It goes onto the fi ber, and the fi ber is wound onto a drum, with very close spacing between the fi bers that is surrounded by this matrix mate- rial. We dry it, and what we end up with is a piece of tape, about 15" wide by 50" long by 0.007–0.008" thick [381 × 1270 × 0.17–0.20 mm].” This tape is provided to a layup team, who again follow a process identi- cal to that of more traditional composite layup: “They cut it into different shapes and lay those pieces over and on top of each other in a tool that imparts the fi nal shape of the part that we’re looking to make,” Wessels said. “The next step is to use an autoclave to bake at tem- perature and pressure—all very similar to PMC—the polymer matrix composite- type process. But then we go on to a couple of extra steps to fully densify the component, and really turn it into a ceramic matrix.”
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“It’s all silicon carbide but now it’s a fi ber within a matrix. And that’s what imparts the toughness.”
The next step is pyrolysis, which burns off all of the organic constituents that are still left inside after the auto- clave process. What’s left behind is a porous lattice made from the ceramic- coated silicon-carbide fi bers in the shape of the desired part. This is then followed by what Wessels terms the melt-infi ltration process:
“This is where we use another fur- nace to basically melt silicon in contact with the part,” Wessels explained. The
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silicon wicks its way into the lattice, turning all of the con- stituents that were left over in that matrix into silicon carbide. “Where previously you had a porous carbon matrix, you end up with a silicon-carbide matrix—it’s all silicon carbide but
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ManufacturingEngineeringMedia.com 81
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