कोबाल्ट-आधारित सुपरअलॉय

Cobalt-based superalloys are austenitic superalloys containing 40-65% cobalt. They exhibit high-temperature strength at temperatures between 730°C and 1100°C, as well as good resistance to hot corrosion and oxidation. They are suitable for manufacturing guide vanes and nozzle guide vanes for aircraft jet engines, industrial gas turbines, and shipboard gas turbines, as well as diesel engine nozzles.

Carbides in cobalt-based superalloys exhibit superior thermal stability. As the temperature rises, the carbides aggregate and grow more slowly than the gamma phase in nickel-based alloys, and their re-dissolution temperature into the matrix is ​​also higher (up to 1100°C). Therefore, the strength of cobalt-based alloys generally decreases more slowly as the temperature rises.

Cobalt-based alloys exhibit excellent hot corrosion resistance. It is generally believed that this advantage over nickel-based alloys stems from the higher melting point of cobalt sulfides (e.g., the Co-Co4S3 eutectic, 877°C) than that of nickel sulfides (e.g., the Ni-Ni3S2 eutectic, 645°C), and the much lower diffusion rate of sulfur in cobalt than in nickel. Furthermore, since most cobalt-based alloys contain more chromium than nickel-based alloys, they can form a protective layer on the alloy surface that resists corrosion by alkali metal sulfates (e.g., Cr2O3, which protects against Na2SO4 corrosion). However, cobalt-based superalloys generally have much lower oxidation resistance than nickel-based alloys.