Chrome Aluminizing

a case-hardening method involving the diffusion of chromium and aluminum into the surface layers of metals and alloys. Depending on the properties desired, the chromium and aluminum are introduced at the same time, which is done most often, or separately (mainly from the gas phase). The process is carried out at temperatures ranging from 950° to 1200°C over a period of six to ten hours. The thickness (usually 20 to 500 microns), the composition, and the properties of the chromium and aluminum layer depend on the nature of the alloy being treated, the method used, and the conditions under which the process is carried out. When the aluminum and chromium are diffused in separately, the properties of the surface layer depend on the order in which the elements are introduced.

Chrome aluminizing is carried out on objects made of steel or alloys based on nickel, molybdenum, niobium, tantalum, cobalt, and copper. It imparts improved resistance to heat, creep, erosion, and corrosion in a nitric-acid medium. It is used to improve the quality and reliability of turbine rotor blades in aircraft engines, as well as the quality of parts in exhaust systems, fire tubes, combustion chambers, and plasma-forming nozzles.