Alternative Coating Technologies to Hexavalent Hard Chrome in a Nuclear Reactor

Westinghouse currently uses “hexavalent” hard chrome on austenitic and ferritic stainless steel components for wear, anti-galling and corrosion protection in the primary side of pressurized water reactors (PWR). With the EU REACH regulations on hexavalent hard chrome, Westinghouse has begun a comprehensive evaluation of various coating technologies to find  suitable alternatives for wear and corrosion protection of affected components. This study assesses the wear and corrosion performance of the various coatings relative to hard chrome. The coatings evaluated in this study include Cold Spray, thermal spray, and High-Phos Electroless Nickel.  The adhesive strength and nanohardness of these coatings were studied followed by microstructural characterization using LOM and SEM.  A comprehensive tribological study, combining sliding and fretting wear, and a study of the corrosion behavior of the coatings in a simulated PWR environment is currently ongoing and is expected to be completed by Q3 2026.  The results of the microstructural and micromechanical characterization strongly suggest that electroless nickel and cold spray coating using Alloy 625/CrC matrix may be good substitutes for hard chrome in PWR applications, but corrosion and wear results would be needed to reach a definitive conclusion.