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Cadmium plating has been used as a corrosion resistant coating for aerospace components for many years. Cadmium plating provides good corrosion resistance with excellent self lubricating properties. In spite of these properties, continuing efforts are underway worldwide to eliminate cadmium because of environmental concerns. Alternative processes are being investigated. Metallic - ceramic coatings which contain active aluminum metal powder as pigment have been proposed as cadmium replacements. These coatings have been in use for many years in air frame applications where cadmium plating could not be used because of part size, temperature exposure extremes, or part configuration. Examples of such components are described. Recently devised dense pack metallic-ceramic coatings show improved performance in which lower cure temperatures are possible and corrosion resistance is significantly upgraded when compared to original formulations.

This paper addresses the use of novel aluminum-filled inorganic coatings on plain carbon steel or stainless steel fasteners in order to eliminate galvanic corrosion in structural assemblies incorporating dissimilar metals. These coatings are described and compared with zinc plated fasteners and other metals in a galvanic series. In environmental testing, stainless steel fasteners and carbon steel fasteners coated with zinc and aluminum-filled coatings, are coupled with aluminum, tin, copper, and 300 series stainless steel. The results of these tests indicate that this sacrificial aluminum/ceramic coating system limits corrosion of steel fasteners more effectively than zinc platings.

Corrosion of the steel compressor disks of gas turbines is a serious problem. In this study, the causes of disk corrosion failure are reviewed; recommended protective coatings and lubricant films are described, and their interactions noted. To evaluate these corrosion resistant coatings, five candidate coatings are described as well as three lubricant/antigallant films commonly used on disks or on blade roots in contact with disks. Results of comparative testing in environmental tests are described for the protective coatings with and without the presence of lubricant films. Data is presented graphically; optical and SEM photomicrographs are included. It is shown that lubricants/antigallants can seriously degrade the performance of all protective coating systems unless great care is taken in selection. Further it is shown that sealed metallic/ceramic coatings provide superior corrosion protection when compared to other coating systems.