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Diffusion Coating

Pack Cementation Aluminizing
      The most common type of coating for environmental protection
of superalloys is the aluminide diffusion coating via pack-powder2-2.jpg
(pack cementation) method, which develops an aluminide (CoAl or NiAl) outer layer with enhanced oxidation resistance. This outer layer is developed by the reaction of aluminum with the nickel or cobalt in the base metal. The oxidation resistance of aluminide coatings is derived from formation of protective Al2O3 scales.
Aluminide diffusion coatings generally are thin, about 2 to 3 mils (50 to 75 µm). They consume some base metal in their formation and, although deposited at intermediate temperatures, are invariably diffused at temperatures of about 1900 to 2050 °F (1040 to 1120 °C)
prior to being placed in service.

SermaLoy J (Praxair®)
   5-5.jpgSermaLoy™ J diffused slurry aluminide coating has a unique silicon-enriched outer layer. It is effective in protecting gas turbine hot section components at temperatures up to 1835°F (1000°C). The presence of silicon on the surface of the coating promotes the formation of a tightly adherent scale of very pure aluminium oxide
(Al2O3) that is very resistant to dissolution by the liquid sulphate salts that cause hot corrosion. The excellent high-temperature oxidation resistance of SermaLoy J coating is due in part to reduced oxygen mobility through the pure alumina as well as to the stabilizing effect that the silicon has upon the aluminide. With the SermaLoy J slurry aluminizing process, each component is coated individually; thus, each can be inspected before diffusion. At this intermediate stage, repair or rework of the slurry coating can be accomplished without any loss of base metal. Using a slurry greatly simplifies masking and allows selective coating of very localized regions which is ideal for restoration  or alternatively, large areas like ducts and burner cans.
Equivalent Products: Ceral® 10, IP®1041, Alseal® 625, LSR® AlSi