Friction controlled material wear testing and selection under starved lubrication

Abstract

Due to the ever increasing number of engineering materials, in particular thermal spray coatings, a means of ranking the tribological behaviour under starved lubrication becomes a necessity. The aim of this paper is to introduce a new wear test technique using a pin-on-disc tribometer (wear machine). The test method introduced allows ranking of materials in sliding contact under partial elastohydrodynamic (EHL) and/or boundary conditions. The ranking is based on the determination of transition pressures from mild to severe wear. These can be determined in short testing times under starved lubrication in the temperature range 20–250 °C. The test procedure, simulated wear mechanisms, contact pressure description and frictional effects with the inclusion of relevant test results and corresponding applications for which the technique has been used are discussed. It is demonstrated that a value known as the critical coefficient of friction μ c is obtained at transition pressures, which is indicative of the material's behaviour in a lubricated system. It is also shown that for a given pair of materials, the same test technique can be utilised to determine the influence of different lubricant formulations on transition pressure. Furthermore, it is indicated that the critical coefficient of friction determined for any given material is a crucial parameter in finding its wear rate using a lubricated constant load pin-on-disc test method.