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Question about Tungsten

Question about Tungsten

Question about Tungsten

(OP)
Hi guys,
As may you know, we (aerospace and turbine engineers) always looking for a material with higher melting point to use in turbine blades and combustion chamber surfaces,
the materials is now using is super alloys like Inconel group, based on nickel molybdenum and chrome, that has the melting point around 1000-1500 degree centigrade.
As i know, the highest melting point between metals are 3500 degree for Tungsten, but i didn't found anything to answer my question, why companies doesn't like to work on it, and its alloys (like Tungsten-cooper, Tungsten-nickel) to reach higher melting points, in combustion chamber and turbine, and increasing turbine inlet temperature, that lead us to producing more power from a same turbine.
i know that, Tungsten is very heavy, but it wouldn't be a problem in a rotating machine (like industrial gas turbines), and its a little brittle that can be solved with add some cooper in alloy.
thank you
Morteza

RE: Question about Tungsten

So far the only W alloys developed (except for TZM) have strength that drops off much faster with rising temp that pure W. To the point that at hot end working temp they are no stronger than existing alloys.
W also is very sensitive to oxidation and it has low toughness at temps below 1000C
The biggest areas of work now are CeramicMatrixComposites and specialty coatings.

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P.E. Metallurgy, Plymouth Tube

RE: Question about Tungsten

(OP)
As i know, one of the basic rules on turbines, is that, as much as you can increase the turbine inlet temperature, the output power of the turbine increases, but the thing here that limit us is the tolerable temp. of the materials, so, why high melting point isn't necessarily a good thing?
now a day blades of first stages of turbines need to bee cooled from inside not to let it melt in high temp.
do you mean that W became pasty in high temperatures?
what about Tungsten Carbide? high melting point and very high hardness.

RE: Question about Tungsten

Mass is very important for turbine blades. Most of the mechanical loading is centrifugal.

je suis charlie

RE: Question about Tungsten

a high melting point makes it more expensive to manufacture.

As an engineer, you should already know that an engineered solution is always a compromise between multiple contradictory requirements. Therefore, no single item, such as melting point can be the sole determinator for picking a material.

TTFN
I can do absolutely anything. I'm an expert!
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers

RE: Question about Tungsten

Melting point does not matter most, strength at the temperature of use is more important.
Well that and thermal properties, fatigue, corrosion resistance, thermal shock resistance, and can you make the part.
Remember that today first stage blades (and vanes) are investment case as single crystal parts with very detailed internal cooling passages.
Most people don't stop and think about the longevity of GTs today. When the 707 (4 engine) was introduced the time for engines on the wing was about 5,000hr. The amount of overhaul that they needed depending on the type of flying that they had seen.
Today a long range twin jet (777,787, A350) will fly 40,000hrs before the engines are pulled.
Engines are complicated systems with blades, bearings, seals, coatings, igniters, injectors, burners, and a very complex control system.

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P.E. Metallurgy, Plymouth Tube

RE: Question about Tungsten

Higher melting point materials do not translate to usable blade material in elevated temperature service. Cost, ease of manufacture, are issues that one must deal with when manufacturing components, like GT turbine blades. Cooling efficiency and blade airfoil coatings will be the design parameters to allow for increased service temperature.

RE: Question about Tungsten

The after market for some of these parts is littered with very poor castings, in India. Some of them, unfit for any use. It is a money looting racket.

I agree with all the comments above, a singular property(high melting point) cannot decide selection of candidate material.


"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

RE: Question about Tungsten

Tungsten works well for vacuum turbines, but there's not much call for those.

Tungsten filaments last for 1000's of hours in vacuum, or partial pressure inert gas environments (light bulbs), but let even a wisp of oxygen, or water, into the mix and poof, it oxidizes to lovely white or yellow smoke. Same thing with carbide. And, there is no good coating to get the carbide or raw tungsten past about 1500 F, or toolmakers would be using it for cutting inserts. Inconels and similar have good oxidation resistance well above 1500F, thus they are the current solution. There was some work being done at NASA with ceramic turbine blades, but the problem there is to make the ceramic part have a repeatable strength; current production methods for ceramics give a lot of variability from part to part, and a turbine is not a part you want to come apart very much...

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