Pratt & Whitney single-crystal turbine blade

Sample passed around. Used to teach hot-section cooling design (boundary-layer cooling, ceramic core casting, seven-thousandths wall thickness limit).

[Tom hands a single-crystal blade sample around.] I also pass around single-crystal blades — I usually find some excuse to pass this around several times. This is from an old Pratt & Whitney engine from the 1980s. It's from the hot section — single-crystal blade. It has cooling ports, that's why I pass it around. It's been filleted; they took a wire EDM and sliced it. It was a single crystal, but it has an internal structure. They cast it for turbulent flow, so you're getting cooling of the hot gases coming through. Hot gases at three thousand degrees Fahrenheit, with a melting temperature of the blade material at twenty-four hundred degrees Fahrenheit.

Mert Shank (formerly MIT 3 faculty) drives directional solidification at Pratt & Whitney. Grain-boundary creep failure mitigated first by columnar growth, then by single crystals. Air-cooled internal channels then enable firing temperature above the alloy melting point (3000°F firing vs 2400°F alloy melt).

Then there started to be a big divergence. What happened in here? This turns out to have been metallurgy too. They went to directional solidification. It was a guy who had been a faculty member here, Mert Shank, who went down to Pratt & Whitney. There's a guy here, Tony Giamei, retired from Pratt & Whitney, who wrote a little article. Here's the turbofan engine. Over here on this page — Professor Flemings used to have these same three on a little plaque back in the mid-1970s when this stuff was all kind of new.

[Tom holds up a sectioned turbine blade.] We passed these around when Dr. Belmar was talking about growing single-crystal turbine blades. This turbine blade would go on either a 747 or 757 type engine. It's a single crystal, and they took it and they cut a fillet in it. Pratt Whitney gave me this. They take a wire EDM and they section it so you can see the inside, and the inside has got all kinds of turbulators because they're going to put cooling gas through here. They pump 1000-degree-Fahrenheit gas as the cooling gas. The outside of this blade is going to see an environment of about 3000-degree-Fahrenheit combustion gas, and it has to be cooled, because if it's not, the metal melts at 2400 degrees Fahrenheit. So if you didn't have cooling gas your engine would melt — not a good thing.

Development arc from uncooled solid blades → nickel superalloys → directionally solidified → single crystal by early 1990s, led at Pratt & Whitney by an MIT-affiliated metallurgist (name garbled in captioning).

People started working on better and better materials. These were uncooled solid materials, and they started going to nickel-based superalloys in the 50s and 60s and 70s. As they went to the nickel-based superalloys, they learned you didn't like finer grain sizes — at high temperature that meant creep; the metal would deform. So they went to directionally solidified turbine blades, and they went to single crystal blades by the early 1990s. The guy who really led that at Pratt & Whitney was Gell [unclear — captioner garble; likely a Pratt & Whitney metallurgist with MIT faculty ties], who had been a faculty member here at MIT in both mechanical and materials. He went to Pratt & Whitney and led all that effort in the 60s.