Replacement of Chromium Electroplating on Gas Turbine Engine Components Using Thermal Spray Coatings

Hard chromium electroplating is extensively used by aircraft manufacturers and military maintenance depots to provide wear and/or corrosion resistance or to restore dimensional tolerance to components. However, chrome plating utilizes hexavalent chromium, which is a highly toxic carcinogen, and increasingly, stringent environmental and worker-safety regulations are making chrome plating more expensive for the DoD. This document constitutes the final report on a project to qualify high-velocity oxygen-fuel (HVOF) and plasma thermal spray coatings as a replacement for hard chrome plating on gas turbine engine components. Extensive fatigue, fretting wear, salt-fog corrosion, and carbon-seal wear tests were performed on HVOF, WC/17Co, Tribaloy 400, Tribaloy 800, and Cr3C2/20(NiCr), and plasma-sprayed Tribaloy 400 coatings compared to hard chromium. In general, the HVOF WC/17Co coatings demonstrated superior performance. An accelerated test on a TF33 engine containing seven components coated with HVOF WC/17Co showed superior performance to what would have been expected using the standard hard chromium. A cost/benefit analysis indicates that military repair depots that overhaul gas turbine engines can realize substantial savings by converting from hard chrome to HVOF. The original document contains color images. Project no. EPP-0023. Performed in cooperation with Rowan Technology Group, Libertyville, IL, GE Aircraft Engines, Cincinnati, OH, Pratt & Whitney, East Hartford, CT, Metcut Research Inc., Cincinnati, OH, and Concurrent Technologies Corp., Johnstown, PA.