One of the important reasons why cobalt alloys are used as aviation material is its excellent thermal stability. Cobalt alloys have a high melting point and thermal conductivity and less thermal expansion after heating. It can be seen from this that cobalt alloys have advantages in thermal stability.
Compared with cobalt alloys, nickel alloys have a higher strength but more brittle. It is easier to be broken on occasions of impact. When the temperature rises to 800℃ (the operating temperature of some engines), nickel alloys can’t be used, while cobalt alloys retain strong.
The stiffness means the ability to resist deformation. Nickel alloys have a lower stiffness than cobalt alloys in various temperature. With the temperatures above 700℃, the properties of nickel alloys are completely destroyed.
Cobalt Chromium Alloy has superior resistance to high-temperature oxidation. Cobalt alloys have excellent resistance to high-temperature oxidation and can be used in the case of 800℃.
Corrosion resistance of both alloys was tested as follows. With 4 m/s rate, combustion air containing 5-5 or 5-6 sea salt, NO. 2 fuel oil (0.3% ~ 0.45% sulfur ), and air – oil ratio for 30:1, the sample was rotated cooled from 800℃ to 260 ℃with cold air every an hour. This dynamic hot corrosion test after the cycle test for 200 hours in the combustion apparatus shows that metal loss portion of the cobalt alloys is significantly lower than that of nickel alloys.
In conclusion, the performance of Cobalt Chrome Alloy is much better than nickel alloys, ensuring the use and life of the products. Cobalt alloys have the following advantages: Above all, the hardness of the cobalt alloys are much lower than that of turbine rotors, which makes it safer. In addition, cobalt alloys have a higher melting point and thermal conductivity, and the amount of thermal expansion after heating is small. It has an advantage in thermal stability. What’s more, the strength of the cobalt alloys are slightly lower at normal temperature, but the elongation is higher. Last, cobalt alloys have excellent resistance to high-temperature oxidation and can be continuously used in an environment of about 800℃. The corrosion resistance of cobalt alloys is much better than that of nickel alloys as well.