Efficacy of coatings and thermochemical treatments to improve wear resistance of axial piston pumps

A former study on wear in helicopter axial piston pumps showed the main wear mechanism in the contacts slipper/swashplate is abrasion due to carbides removal. Resulting debris and particles pollute the lubricating fluid leading to abrasive wear in most contacts. Accordingly, surface treatments on the swashplate steel are proposed to reduce slipper/swashplate wear. This study consists in a multitechnical experimental analysis of these solutions in dry and lubricated conditions. With lubricant, steel without treatment suffers carbide removal. PTFE coating prevents it by diminishing the coefficient of friction but are less resistant in highly loaded contact. Nitriding results in higher wear resistance, especially when lubricated. (DLC + WC) coating is the most efficient in dry conditions by minimizing friction coefficient and wear rate.