Turbine engine shroud blade tip wear and repair

Physical demonstration with an in-service shroud piece. Used to explain why blade tips wear, why honeycomb shroud structures are designed compliant, and how directed-energy deposition rebuilds the tip to extend blade life by 30,000 hours and save $2,000–$3,000 per blade.

In fact that's why I brought this, and that's why I drew this picture. [Tom indicates a turbine engine diagram and a shroud piece.] It's a turbine engine. You've got a center shaft, you've got some compressor blades, and you've got some combustors where you add the fuel and the compressed air. Then those go past the turbine blades. Those turbine blades spin this whole thing. As they spin this whole thing, the compressor blades compress the air by about a factor of thirty in volume, but it's going up in temperature, so you get to like thousand psi pressures. But you've got a problem. You don't want any blowback. When you've got high pressure here and atmospheric pressure out here, if you don't have a good seal between the shroud and the blade, you're going to be losing efficiency as the air goes the other way.

Physical artifact (used shroud) shown to class. Honeycomb seal mechanics: three-to-four-thousandths nickel superalloy sheet, designed to be cut into by creeping turbine blades to establish a self-fitting seal. Transition from gold-nickel braze (non-eroding) to nickel-phosphorus/-carbon/-boron brazes (require chromium/palladium inhibitors against base-metal erosion). Cost driver for transition: 1980 gold price spike from $200 to $800/oz.