Search Results

The corrosion of active metals such as magnesium and aluminum continues in spite of the recent development of more corrosion resistant alloys. Much of the corrosion occurs due to chloride ion attack aggravated by design problems that produce crevices and other corrosion prone surfaces. Many components made of obsolete alloys remain in service. In this paper basic protection schemes are reviewed for both magnesium and aluminum. Pretreatments and coating systems typically used are outlined with emphasis on problems at overhaul and reassembly. A novel coating primer/sealer process is described which provides a significantly more corrosion resistant surface for both magnesium and aluminum alloys. A mechanism for the operation of the coating film is offered; how it is combined with pretreatments to seal and prime the active metal surface is described. Data is supplied indicating corrosion resistance in salt spray tests, humidity tests and exposure to aerospace fluids.

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.

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.

Coatings continue to be used on steel compressor components to maximize component life and compressor efficiency. Aluminum-ceramic coatings have been used on steel compressor components for a quarter of a century. During this time, coating application processes have been continually refined for improved performance. These processes are reviewed and a new process included - SermeTel Process 5380 DP. In this process, both coating material and process changes are made to produce finished coatings having improved surface finish, corrosion resistance and erosion properties. Test data is presented for comparison with earlier coating systems. For over twenty-five years, metallic-ceramic coatings have been successfully used on steel components of turbine engines to combat corrosion and erosion. The basic coating of this type, SermeTel W®, continues to be used in a variety of applications and is a base line from which new and improved coating systems can be compared.

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.