The melting point of tungsten is higher than that of rhenium. Why is rhenium alloy more suitable for aeroengine blades?
Although the melting point of tungsten is higher than that of rhenium, it is more difficult to process tungsten alloy, more brittle at high temperature, and more easily oxidized. Rhenium alloy is easy to process and has good creep resistance and oxidation resistance at high temperature, which makes rhenium a very important metal in the space field, especially in the high-temperature parts of jet engines. However, the biggest problem with rhenium is that it is very rare and its annual output is very low.
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 is 3180 ℃
The density of 21.4 g/cm3
Tungsten (W)
Atomic number 74
Melting point is 3410 ℃
The density of 19.35 g/cm3
It can be seen that the density of the metal rhenium is higher than that of tungsten, and the melting point is about 200 degrees lower than that of tungsten. The block rhenium metal is silver white, and its atoms are arranged in a hexagonal densely arranged crystal structure. It has very stable chemical properties and strong acid resistance, and even the water regia can not be dissolved at room temperature.
Rhenium was discovered in 1925, and is the last stable element to be discovered. According to 2014 data, the world's proven rhenium resources are about 2500 tons, which is only one percent of gold, so it 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 rhenium resource reserves is about 250 tons, mainly exists in molybdenite, the content of rhenium in molybdenite is between one in ten thousand ~ three in ten thousand, Shaanxi Province, China's molybdenum ore mountain rhenium reserves are 176 tons.
At present, the global annual production of rhenium is about 50 tons, the price of rhenium in 2016 is 47 million yuan/ton, about one-fifth of the price of gold, 13 times the price of silver, with dwindling rhenium resources, the price of rhenium has risen sharply in recent years, and the international rhenium resources are mainly controlled by western countries.
Adding rhenium alloy (content generally in 3%~6%), has good creep resistance and oxidation resistance, can withstand the high temperature of more than 1500℃, is an excellent aerospace high-temperature materials, such as aeroengine single crystal turbine blade, rocket nozzle and so on, there is no more excellent high-temperature materials than rhenium alloy.
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.
