Aluminizing is a thermo-chemical diffusion process applied to increase the oxidation and corrosion resistance of stainless and other alloy steels. It is also used in nickel and cobalt based alloys to achieve greater creep resistance, hardness and corrosion resistance.
Aluminizing is usually done at a relatively high temperature of 800-1000°C with long residence times depending on the rate of diffusion. While these temperatures are sufficient for steel groups, the aluminization temperature for Ni-based alloys and Ti-based alloys should be 1000-1100°C.
The atmosphere in aluminization furnaces can be argon or hydrogen atmosphere. The properties of the alumina powders used may vary depending on the coating method. In some cases, the purity of powders must exceed 99.9%. Again, the size of the powders is limited to 10 microns in some cases.
What is the thickness of the aluminization coating?
It would be more accurate to give the exact answer to this question depending on the application, but a thickness between 30-80 microns can be achieved.
Aluminized parts can also be coated with another thermal barrier coating later, depending on where they will be used. This is used especially in aerospace applications.
Coating methods
Coating in the box: (pack coating or pack cementation)
Similar to box cementation, one of the oldest diffusion methods, workpieces are placed in a box, embedded in aluminizing powder, and heated in a furnace.
Vapor Phase Coating: (Vapor Phase Coating)
It is a newer technology than box coating. Parts are coated in a vapor phase coating system where the workpiece is placed on top of donor materials so that the surface of the parts will not become contaminated through contact with dust. The coating process is performed by condensing the coating elements that evaporate from the donor material onto the workpiece. Vapor Phase Aluminizing (VPA) and Vapor Phase Chromizing (VPC) are typical coating processes for this method.
Chemical Vapor Deposition: (Chemical Vapor Deposition)
The most advanced method of coating is based on the principle of producing the coating on the workpiece by reacting the donor material with halide-forming gases. The deposition rate can be controlled by adjusting the temperature and gas flow rates.
Scope of application
Aviation engine applications
Parts exposed to temperature and corrosion in chemical plants
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