Examination of Tungsten Carbide Coated Helicopter Main Rotor Hub Components with Coating Chips from Sulfurous Salt Fog Exposure

A helicopter swashplate collective sleeve and tilt-ball were found to have chipping of the tungsten carbide coating. It was determined that corrosion of the substrate alloy created an oxide that expanded and pushed on the coating underneath and created a pockmark in the coating. Attempts to replicate the failure mode was largely unsuccessful in a salt fog chamber but did reveal itself in a sulfurous salt fog chamber. Test specimens were made with improved variations of tungsten carbide compositions in the lab and on an aircraft.