Why is not Tungsten Used in Aero Engines?

Tungsten is the single metal with the highest melting point in the world, and its melting point is as high as 3380 ℃. In comparison, the melting point of iron is only 1538 ° C, and that of nickel is 1455 ° C. So we usually use tungsten as filament in incandescent bulb, because only this kind of metal can withstand the huge heat generated by current passing through.

In terms of high temperature resistance, there are more places where aeroengines need high temperature resistant materials. The aeroengine needs to generate a lot of energy through extremely fierce combustion to drive the aircraft to fly, resulting in a temperature of up to 2000 ℃ or even higher behind the combustion chamber.

But we seldom see tungsten in the main structure of aeroengine, even no compound containing tungsten. Why?

1. A material not only looks at a certain parameter
High melting point is the advantage of tungsten metal, but a material is far from the "melting point" parameter, but includes rigidity, strength, density, price, machinability Wait, when we choose, we need to consider all kinds of factors.

For example, the material in the aeroengine should focus on the rigidity, strength and density of the material. The material with large rigidity will not produce large deformation when the structure is stressed. The high strength means that the material can bear more force without fracture. The density of the material is also very important in the aeroengine. In addition to the weight reduction of the aeroengine itself, the more important thing is that the aeroengine needs to fly to the sky. Therefore, reducing the density of the material can more easily obtain better performance.

Therefore, even though tungsten metal has a high melting point, the density of tungsten metal is 19g / cm3, twice that of steel and four times that of titanium alloy. So it's hard to apply such a large density in aeroengine.

2. Tungsten is not suitable for casting
Tungsten has a high melting point, which is an advantage, but it also shows that many materials processing methods we have been used to are not suitable for tungsten, for example, the technology related to "casting" is difficult to apply to tungsten.

At the same time, tungsten has high hardness and brittleness, so it is often used to make machining tool head, which also represents that tungsten steel is a very difficult material to process. Therefore, the problem of machining also limits the use of tungsten in aeroengine.

3. High melting point does not mean it can be used at high temperature
The melting point of a metal means that it will melt into a liquid at a certain temperature. A metal with a high melting point means that it can remain solid at high temperatures. But keeping solid does not mean that the metal can have necessary mechanical properties.

Although the melting point of tungsten is as high as 3380 ℃, but the temperature is over 1000 ℃, the performance of the material has declined greatly, let alone the amazing density. Therefore, the high melting point of tungsten is exactly "no use in the middle".

4. Rhenium may be more suitable for Aeroengine
Rhenium has a very high melting point (3180 ℃), slightly lower than tungsten, but compared with tungsten, this metal is not so "brittle", but also has better creep resistance at high temperature, and the mechanical properties at high temperature are not as severe as tungsten falling.

So even though rhenium has a lower melting point than tungsten, a higher density than tungsten (the density of rhenium is as high as 21.04g / cm3), and not much better processing performance than tungsten, it is still a super heavy metal that has been initially applied in the field of aerospace because it still has acceptable material properties under high temperature.