Jet engines work at a higher temperature that the melting point of Titanium Superalloy so how do they not melt?
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They pump cool air through them, which exits out of holes on the leading edge, and sometimes the surface, of the blade. This creates a thin layer of cool air on the outside surface.
Temperature is really irrelevant here as long as you can cool off the engine with auxiliary processes. For one, these engines are coated with thermal barrier coatings. There’s also a technique, which I believe answers your question directly, “film cooling” that simply channels the cooler air to the engine surface and reduce the incoming hot air’s effect. This means that the temperate lowers down before it even touches to the surface.
Cooling channels in the blades. They bleed cooler air through and out of little holes in the things which in addition to cooling the blade, also adds a thin buffer layer of cool(er) air over the blade. Additionally the blades generally get coated with a thin high temp layer that isn’t as mechanically strong, but has better high temp properties. Could be Nickel Aluminum which seems to be the go-to for jets, or a ceramic coating which seems more used in like power station gas turbines.
Heat doesn’t transfer instantly. If you can cool off a material faster than the exhaust gases can transfer heat into it you end up in a balance where the material ends up at some temperature in between.
They do experience some degradation over time, from elevated temps, but they won’t get hot enough to melt or fail for their rated lifetime.
they blow cold air through them, watch AgentJayZ on youtube to to learn more than you ever wanted to know about turbine engines
Turbine blades are usually some Nickel based superalloy (particularly the high pressure turbines). Believe it or not they aren’t the most thermally stressed portion, that honor goes to the hot spots on the stator. That is the non rotating ‘blade’ that turns and accelerates the hot gases coming from the combustor so that they hit the turning blade just right.
They are usually made from an alloy that not only has a high melting temperature but also retain strength to very close that temperature. They are then coated with a thermal barrier in the form of a ceramic. After that you take air from the compressor which is hot but still cooler and inject it through the vane (cools it) but then make it go out through carefully designed holes on the surface so that the cooler air comes out n a thin layer like a shield over the surface creating an air curtain that further shields it.
It is probably one of the most engineered portions of the engine and designed so that it can take the hottest combustion air coming from the combustor. That air is not uniformly hot but has some spots that tend to not move much and are really hot.
The rotating turbine blade on the other hand is moving through that hot spot but also through the coolest spot so it sees more of an average. It does however have to stay together while being pulled hard so it also needs cooling but the thermal input is lower than for the static vanes. Also as you move down the cascade of turbines extracting power from the gases they cool down and life gets easier.
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Turbine blades in jet engines are not made of titanium alloys. Titanium alloys do not have the strength or high temperatures properties of steel alloys, let alone nickel alloys. Most turbine blades in jet engines are made of a nickel alloy. Stronger and better properties at high temperatures.
On top of that, turbines in most jet engines are no where near the melting point. Most turbines run in a range of 600-900 deg C(of the aircraft I have flown at least). There will be higher temps on the leading edge and high pressure side of the blades however, with adiabatic heating contributing a lot to those hot spots.
Titanium is used in steam turbines however. Steam turbines are massive, with long blades, and run at relatively low temperatures. The light weight and high specific strength of titanium make it a good choice in this application, giving it good efficiency and corrosion resistance.
You should research GE who is the only successful engine manufacturer so far that has used a ceramic type compound in their blades for extreme heat endurance.
Who knew turbine blades were so cool? Literally.
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