Wear transition of a lubricated sliding steel contact as a function of surface texture anisotropy and formation of boundary layers

This article presents an experimental study of how the transition from mild to severe running conditions of a lubricated sliding steel contact depends on surface texture anisotropy and boundary layers formation. An experimental series was performed on a lubricated sliding ball-on-disc test machine with the capability to make quick but controlled transient single-pass tests. The test discs were finely ground with a strongly anisotropic surface texture. The transition tests were performed at 18 different sliding velocities between 0.038 and 1.19 m/s. For each sliding velocity, the applied load was increased with a constant load rate from zero to a pre-defined load level before the disc had rotated one turn. The first contact between the disc and the ball was arbitrary in relation to the topography orientation for the different tests. Four different states of the test discs were studied: as machined; oxidised by increased temperature in air; pre-treated by immersion in the lubricant and then heating; and pre-treated by applying the lubricant on heated discs. The lubricant was an ISO VG 150 paraffinic mineral oil with triphenylphosphorothionate (TPPT) and phosphorous–nitrogen (PN) additives. The test results show that the load level at which the graduate development from local to complete failure strongly depends on the surface texture orientation relative the sliding direction. The results also show that pre-formed boundary layers decrease the risk of wear transition.