Coating and treatment solutions for rolling/sliding component contacts

Electro-mechanical mechanisms are being increasingly employed to replace existing hydraulic systems to give weight savings, greater accuracy and speed and lower maintenance. The new systems commonly employ rolling/sliding contacts (as found in rolling element bearings, for example) and may have to operate at high contact pressures. They can also be relatively safety critical so failures such as jamming could have serious implications. The aim of this work was to investigate the performance of potential surface treatments and coatings for the surfaces of components in a rolling/sliding contact. The focus was on wear and friction levels. A rolling/sliding test method using two discs made from a high quality steel (nitrogen martensitic stainless bearing steel) used in manufacturing precision components. One disc was curved (this disc was coated/treated) and one was flat (this disc was untreated). A contact pressure of 3.65 GPa (typical of the maximum contact pressure that could be seen in such contacts) and a slip level of 0.5% were used. Tests were run lubricated (with a multi-purpose synthetic grease with lithium soap) and dry, to represent the worst case scenario. The worn surfaces were analysed and friction was assessed and compared to that seen with the untreated base material. Performance of the treatments and coatings were ranked to select those to take forward to full-scale component testing.