Metal Finishing Guide Book


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for cadmium replacement were identified. Due to the particular focus of this project, candidates were limited to commercially available or near-commercial technologies. These include: • • • • • • • • • • • • Advanced materials Alloys deposited by chemical vapor deposition (CVD) Alloys deposited by molten salt bath processes Alloys deposited by ionic liquid processes Electrodeposited aluminum and alloys Electroless nickel technologies Electroplated tin alloys Electroplated zinc-cobalt Electroplated zinc-nickel Ion vapor deposited (IVD) aluminum and alloys Metal-filled paints and ceramics Sputtered aluminum and alloys The viability of each of these processes in the context of the specific application—electrical connector shells—is discussed herein. Where data is available, issues such as compatibility of the alternatives with existing cadmium-plated connectors will be addressed. ADVANCED MATERIALS The use of advanced materials as a replacement for cadmium-plated parts has been considered mostly for larger aerospace components. Stainless steel is the most likely candidate to replace cadmium on larger, non-electric components. A corrosion-resistant stainless steel, S53, was developed under a project funded by the Strategic Environment Research and Development Program (SERDP). This effort1, 5, 8 focused on providing corrosion protection and resistance to stress corrosion cracking on aircraft landing gear. Stainless steel alloys would provide many of the necessary properties needed for electrical connector shells and may be acceptable for some applications. However, these materials generally exhibit a high mating resistance and also may not be cost-effective. Likewise, titanium alloys and Inconel¨ have been found to be adequate as substrate substitutes for cadmium plated fasteners5, but these may also be cost prohibitive for use in electrical connectors. Polymer composite materials (such as polyetheretherketone) are already in use in some commercial applications. However, military usage appears to be minimal (at least for ground vehicle applications), and consideration of this material introduces issues related to cost, conductivity, and mechanical wear for some applications. Overall, it is evident that additional research and development is required to use advanced materials to replace the standard shells in newer models of electrical connectors. ALLOYS DEPOSITED BY CHEMICAL VAPOR DEPOSITION The Air Force Research Laboratory (AFRL) evaluated aluminum coatings applied through Atmospheric Pressure Chemical Vapor Deposition (APCVD).9 Environmentally benign CVD processes using triethylaluminum as a precursor for producing high-quality aluminum coatings was explored. While promising, this process involves special high-cost, equipment. Considerable further devel352

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