Nickel aluminide coatings are used in the aerospace industry to provide high temperature oxidation protection for nickel alloy jet engine parts. To form a nickel aluminide coating, the part to be coated is placed in a coating box or retort and covered in a powder composed of aluminum or an alloy of aluminum, calcined aluminum oxide powder (as an inert filler) and a halogen generating carrier compound which upon heating to a suitable temperature, places aluminum atoms in contact with the basic nickel containing surface. In this procedure, a chemical reaction takes place with the result being alloying of nickel (cobalt, iron or other suitable element) from the basis metal with aluminum from the coating powder. During engine operation, the resultant coating forms an extremely dense oxide layer on the metal surface preventing any further oxidation and subsequent attack of the basis metal. This improves the lifetime of the part.
During operation, however, the coating may become damaged due to the operational environment. If the coating of the entire part was abraded away, the entire part could be retreated.
Generally, however, the coating becomes damaged only in a small area. General Electric Company currently markets a Codal repair tape which is an iron aluminum alloy used in tape form. This uses some type of acrylic or other binding system which is proprietary to the General Electric Company. However, this tape is generally unsuitable because it is stiff and has a shelf life. It is preferred, however, to use a localized aluminide coating application.