How turbine blades are made

Cooled turbine blades run in gas near 1,370 °C, so each is cast around a ceramic maze of cooling channels.

stations: 8
things upstream: 38
raw sources: 20
steps from the ground: 6

The short version

A turbine blade is cast from nickel superalloy by the lost-wax method. A wax copy of the blade, wrapped around a ceramic core that will leave cooling passages, is dipped in ceramic to build a shell. The wax is melted out, metal is poured in, and the blade is finished, drilled with tiny holes and coated.

Inject a wax blade

Molten wax is injected into a metal die in the exact shape of the blade. If the blade is hollow, a ceramic core in the shape of its cooling passages is placed in the die first.

Goes in
Paraffin wax
Dip into a ceramic shell

Wax blades are fixed onto a central wax stalk and dipped over and over into ceramic slurry and sand. The layers dry into a hard, heat-resistant shell.

Goes in
Ceramic
Melt out the wax

Steam or heat drains the wax from the shell, leaving a hollow mold of the blade. The wax can often be reused.
Pour in the superalloy

Superalloy based on nickel is melted in a vacuum and poured into the hot shell. Nickel keeps its strength at temperatures where steel would soften.

Goes in
Nickel Cobalt Chromium
Grow a single crystal

In the best blades the metal is cooled slowly so that it solidifies as one single crystal. With no grain boundaries across the blade, it creeps far less at high temperatures.
Break the shell and drill cooling holes

The shell is knocked off and the ceramic core is dissolved away. Lasers or electrical discharge then drill tiny holes through which cool air will pour over the blade skin.
Add a thermal barrier coating

A thin layer of ceramic coating is applied to insulate the metal from the hot gas.

Goes in
Ceramic
Scan every blade

Blades are checked for hidden flaws, wall thickness and airflow through the cooling holes. One blade that fails can wreck an engine.

End of the lineTurbine blade Next it goes into jet engine.

Worth repeating

Military engines like the Snecma M88 can see turbine temperatures of 1,590 °C.
Ceramic matrix composites can withstand temperatures 200 to 300 °F higher than superalloys.