Validation of HVOF WC/Co Thermal Spray Coatings as a Replacement for Hard Chrome Plating on Aircraft Landing Gear

Abstract

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 quality high-velocity oxygen-fuel (HVOF) thermal spray WC/Co coatings as a replacement for hard chrome plating on landing gear components. Extensive fatigue, wear, corrosion, impact, and hydrogen embrittlement test results comparing the WC/Co coatings against hard chrome are presented. The results of rig and flight-testing of HVOF WC/Co coatings on landing gear components are also presented. in general, the performance of the WC/Co coatings was superior to hard chrome. Producibility issues such as stripping, grinding, and non-destructive inspection of the coatings were addressed. Cost/Benefit analyses indicate that military repair depots that overhaul landing gear can realize substantial savings by converting from hard chrome to HVOF. Specifications were developed for the WC/Co powder, the coatings deposition parameters, and the grinding of the WC/Co coatings.