Electroactive Polymers as Environmentally Benign Coating Replacements for Cadmium Plating on High Strength Steels

Despite environmental hazards, cadmium (Cd) is still widely used in the plating industry (especially for fasteners) because of its unique combination of properties. There is no drop-in replacement for Cd-plated high-strength steels, but commercial zinc (Zn) and aluminum (Al)-filled polymers deposited by the dip-spin coating technique have shown initial promise. Although they are quite effective, the coating tends to clog fastener threads, and their torque characteristics tend to change over the course of multiple assemblies. This is a serious drawback for aerospace and other DoD applications where weapon systems require periodic strip-down and maintenance. In order to meet the environmental challenge of replacing Cd on high strength steel substrates without the loss of performance, a novel approach using electro-active polymers (EAP s) as the corrosion inhibition layer has been investigated. All of the objectives of this SERDP SEED have been accomplished successfully. The synthesis and characterization of new monomers and the synthesis, using electroless deposition techniques and electropolymerization of EAPs that adhere to steel substrates has been completed. Both electropolymerization and electroless deposition are non-lineof- sight (NLS) techniques for coating EAPs onto steel plates and other geometries. The characterization of critical coating properties, using a combination of standard methods for fastener performance such as galling testing and hydrogen embrittlement testing, along with an evaluation of corrosion performance using impedance spectroscopy and neutral salt fog testing, EDS/SEM, has also been completed.