Replacement of Chromium Electroplating on Landing Gear Components Using HVOF Thermal Spray Coatings

Abstract

Abstract : Electrolytic hard chrome (EHC) plating is a technique that has been in commercial production for more than 50 years. It is a critical process that is used for applying hard coatings to a variety of aircraft components in manufacturing operations and for general rebuild of worn or corroded components removed from aircraft during overhaul. In particular, chrome plating is used extensively on landing gear components such as axles, hydraulic cylinders, pins, and journals. Chromium (Cr) plating baths contain chromic acid, in which the chromium is in the hexavalent state, with hexavalent chromium (hex-Cr) being a known carcinogen. During operation, chrome plating tanks emit a hex-Cr mist into the air, which must be ducted away and removed by scrubbers. Wastes generated from plating operations must be disposed of as hazardous waste, and plating operations must abide by U.S. Environmental Protection Agency (EPA) emissions standards and Occupational Safety and Health Administration (OSHA) permissible exposure limits (PEL). Recent studies have clearly shown a significant number of deaths at the current PEL of 100 Fg/m3, prompting OSHA to explore significantly reducing the hex-Cr PEL. A Navy/Industry task group concluded that the cost of compliance for all Navy operations that use hex-Cr (i.e., not just plating) would be more than $10 million to reduce the PEL to less than 5 Fg/m3. Previous research and development efforts [1,2] had established that high-velocity oxygen-fuel (HVOF) thermal spray coatings are the leading candidates for replacement of hard chrome. HVOF thermal spraying can be used to deposit both metal alloy and ceramic/metal (cermet) such as tungsten carbide/cobalt (WC/Co) coatings that are dense and highly adherent to the base material. They can also be applied to thicknesses in the same range as that currently being used for EHC. Currently, there are HVOF thermal spray systems commercially available.