The Role of Surface Texture on Friction and Transfer Layer Formation - A Study of Aluminium and Steel Pair using Pin-on-Plate Sliding Tester

Surface texture of a tool plays an important role as it primarily controls the frictional behavior at the tribo interface. In the present investigation, pin-on-plate sliding tester was used to identify the effect of directionality of surface grinding marks on coefficient of friction and transfer layer formation. 080 M40 steel plates were ground to achieve different surface roughness with unidirectional grinding marks. Super purity aluminium pins were slid at a sliding velocity of 2 mm/s against the prepared steel plates. Grinding angle (i.e., the angle between direction of sliding and grinding marks) was varied between 0 o and 90 o in the tests. Normal load was varied from 0 to 120 N during the tests. Experiments were conducted under both dry and lubricated conditions in ambient environment. Scanning electron micrographs of the contact surfaces of pins and plates were used to study the surface features that included the morphology of the transfer layer. Surface roughness parameters of the steel plates were measured in the direction of the sliding using an optical profilometer. It was observed that the coefficient of friction and transfer layer formation depends primarily on the directionality of the grinding marks of the harder mating surface. Under lubricated conditions, stick-slip phenomena was observed, the amplitude of which depends on the plowing component of friction. The presence of stick-slip motion under lubricated conditions could be attributed to the molecular deformation of the lubricant component confined between asperities. The grinding angle effect on coefficient of friction was attributed to the variation in plowing component of friction, which in turn depends on the mean slope of the profile of the harder mating surface.