Electroplated Hard Chromium Replacements for Dod and OEM Landing Gear Applications

Cost effective alternatives to electroplated hard chromium (EHC) that can provide comparable performance, reduce compliance burdens, and address worker safety concerns have been sought by the United States Air Force (USAF) for nearly 20 years.  During these investigations, environmental, safety, and health regulations have become more stringent. The Occupational Safety and Health Administration permissible exposure limits for hexavalent chromium [Cr(VI)] have been reduced to 5.0 micrograms per cubic meter (μg/m³) of air as an 8-hour time weighted average (TWA), and the American Conference of Government Industrial Hygienists threshold limit values for Cr(VI) have been reduced to 50 μg/m³ for water soluble compounds and 10 μg/m³ for insoluble compounds as an 8-hour TWA.  As a result, implementing EHC alternatives for complex geometries continues to be a need for the USAF Air Logistics Centers and original equipment manufacturers. To address this need, work has been performed to fully optimize and test electrolessly deposited nickel-phosphorus coatings with occluded silicon carbide (SiC) particles and electrodeposited cobalt-phosphorus (Co-P) coatings with occluded SiC particles.  More recently, a newly formulated nano-cobalt phosphorus coating with proprietary occluded particles has been included in the investigation. This presentation will discuss the results that were obtained to date to address EHC replacements for landing gear applications. The composite coating properties are being compared to those of EHC as well as a benchmark coating, nanostructured Co-P.