Molybdenum is a very important alloy element in high-performance nickel-based alloys. It is divided into two basic types: 1. Solid solution strengthened 2. Age hardening.
In corrosion-resistant nickel-based alloys, an important role of molybdenum is to give the alloy resistance to non-oxidizing media such as hydrohalic acids (HCl, HBr and HF) and sulfuric acid. Therefore, the alloy with the strongest corrosion resistance to this type of environment is the B3 alloy with a molybdenum content of 28.5%. At the same time, molybdenum and chromium together provide the alloy with resistance to local corrosion such as pitting and crevice corrosion. Alloys C22 and C2000 are particularly resistant to this type of corrosion.
Corrosion-resistant nickel-based alloys are widely used in chemical, oil and gas, petrochemical, pharmaceutical, and pollution control industries, where highly corrosive environments are very common.
In high temperature alloys, molybdenum is often added to resist high temperature creep damage. For solid solution strengthened alloys, molybdenum diffuses very slowly in nickel. Since high temperature creep is usually diffusion controlled, the addition of molybdenum is very effective in reducing the creep rate. For age-hardened alloys precipitated by γ ', Ni 3 (Al, TI), the addition of molybdenum can strengthen the matrix and reduce the lattice mismatch between the matrix and the γ' phase, thereby improving the stability of the precipitates. The role of molybdenum in 242 alloy is very unique. The specific combination of molybdenum and chromium promotes the formation of long-range ordered Ni 2 (Mo, Cr) phase particles, which makes the alloy have high strength without significant reduction in ductility. In addition, the addition of molybdenum is also very effective in reducing the coefficient of thermal expansion.
In order to take full advantage of this effect, the gas turbine seal ring is made of high-molybdenum alloy 242. High temperature alloys are widely used in gas turbine components such as turbine disks, combustion chambers, transition ducts, turbine casings, seal rings, afterburner components and thrust reversers. They are also used in industrial heating equipment, heat treatment, heat exchangers, mineral processing and waste incineration.
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