Tungsten has a higher melting point than rhenium. Why is rhenium alloy more suitable for aero-engine blades?
Although tungsten has a higher melting point than rhenium, tungsten alloys are also more difficult to process, more brittle at high temperatures, and more easily oxidized. Rhenium alloys are easier to process and have excellent creep resistance and oxidation resistance at high temperatures, making it an important metal for aerospace applications, especially in high-temperature parts of jet engines. But the biggest problem with rhenium is that it is rare and has low annual production.
Tungsten and rhenium: Tungsten and rhenium are the two metals with the highest melting points. Their physical properties are as follows:
Rhenium (Re) : Atomic number 75 Melting point 3180℃ Density 21.4g/cm3
Tungsten (W) : Atomic number 74 Melting point 3410℃ Density 19.35g/cm3
Can see, the density of metal rhenium is higher than tungsten, melting point is lower than tungsten about 200 degrees, massive rhenium metal is silvery white, its atomic arrangement shows hexagonal close row crystal structure, chemical property is very stable, have very strong acid resistance, below normal temperature even aqua regal also can not be dissolved.
Rhenium is an element discovered in 1925, is also the last stable element to be discovered, 2014 data, the global proven resources of rhenium is about 2,500 tons, only one percent of gold, can be said to be quite rare, and half of the rhenium resources are located in Chile in South America.
According to the data in 2020, China's proven reserves of rhenium resources is about 250 tons, mainly exists in molybdenite, the content of rhenium in the molybdenite between 1/10000 ~ 3/10000, China's Shaanxi Province of molybdenum mine mountain rhenium reserves are 176 tons.
Annual global production of rhenium is about 50 tons. In 2016, the price of rhenium was 47 million yuan/ton, about a fifth of the price of gold and 13 times the price of silver. The price of rhenium has risen sharply in recent years as resources of rhenium become scarcer, and the international rhenium resource is mainly controlled by Western countries.
Alloys with rhenium (the content is generally 3%~6%) have good creep resistance and oxidation resistance, and can withstand high temperatures above 1500℃. They are excellent high temperature materials in the field of aerospace, such as single-crystal turbine blades of aero-engines, rocket nozzles, etc. At present, no superior high temperature materials than rhenium alloy have been found.
Early space high temperature material also use tungsten alloy, but the disadvantage of tungsten is very obvious, first of all, tungsten brittle, processing difficulties, oxidation resistance is not good, tungsten is slow oxidation during temperature higher than 1000 ℃, this will reduce the life of the aerospace engines, and join the rhenium alloy is maintained a very good high temperature performance, so for aeroengine blade, The metal rhenium is superior to tungsten.