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, the processing difficulty of tungsten alloy is also higher, which is more brittle at high temperature and easier to be oxidized; While rhenium alloy is easier to process, which has good creep resistance and oxidation resistance at high temperature, which makes rhenium become a very important metal in the aerospace field, especially the high-temperature parts of jet engine. However, the biggest problem of rhenium is that it is very rare and has high yield. The quantity is very low.
Tungsten and rhenium
Tungsten and rhenium are the two metals with the highest melting point. Rhenium (Re) with atomic number 75, melting point 3180 ℃, density 21.4g/cm3. Tungsten (W) with atomic number 74, melting point 3410 ℃, density 19.35g/cm3.
It can be seen that the density of rhenium is higher than that of tungsten, and its melting point is about 200 degrees lower than that of tungsten. The massive rhenium metal is silver white, and its atoms are arranged in hexagonal close packed crystal structure. Its chemical properties are very stable, and it has strong acid resistance, and even aqua regia cannot be dissolved at room temperature.
Rhenium was discovered in 1925, and it is also the last stable element. According to the data in 2014, the world's proven rhenium resources are about 2500 tons, only one percent of gold, which can be said to be quite rare, and half of them are located in Chile, South America.
According to the data in 2020, the proven rhenium resource reserves in China are about 250 tons, mainly in molybdenite. The content of rhenium in molybdenite is between 1 / 10000 and 3 / 10000. The reserves of rhenium in Huanglongpu molybdenum mine in Shaanxi Province are 176 tons.
At present, the annual production of rhenium in the world is about 50 tons. In 2016, the price of rhenium was 47 million yuan / ton, about one fifth of the price of gold and 13 times of the price of silver. With less and less rhenium resources, the price of rhenium has increased significantly in recent years, and the international rhenium resources are mainly controlled by western countries.
The alloy with rhenium (generally 3% ~ 6%) has good creep resistance and oxidation resistance, and can withstand the high temperature above 1500 ℃. It is an excellent high temperature material in aerospace field, such as single crystal turbine blade of aeroengine, rocket nozzle and so on. At present, there is no more excellent high temperature material than rhenium alloy.
Tungsten alloy was also used in the early Aerospace high-temperature materials, but the disadvantages of tungsten are very obvious. First of all, tungsten has poor brittleness, difficult processing, and poor oxidation resistance. When the temperature is higher than 1000 ℃, tungsten will slowly oxidize, which will greatly reduce the life of aerospace engine. However, the alloy added with rhenium maintains good high-temperature performance. Therefore, for aero-engine blades, metal rhenium is better than metal Tungsten is excellent.
