Effects of Contact on the Abrasiveness of a Thin Boron Carbide Coating

Abstract

Boron carbide (B4C) has been studied under dry sliding conditions for use as a potential finite-life run-in coating. Such a coating has been found to polish its mating surface during dry sliding wear, thereby providing fatigue resistance to the coated part. Employing such run-in coatings requires a complete understanding of the changes that occur in the coating abrasiveness during the polishing process. Therefore, a thorough understanding of the changes in the contact conditions of such a system needs to be obtained. This study presents the role that contact plays in changes of the overall coating abrasiveness. By performing sliding wear experiments using various contact conditions, i.e. ball-on-disc, pin-on-disc and cone-on-disc, we directly investigated the effects of macro-scale contact conditions on the coating abrasiveness. It was found that the rate at which the coating abrasiveness decreased was independent of the macro-scale contact conditions. These findings were further validated by investigating the coating abrasiveness results that were obtained by performing spiral track wear experiments. Through the use of a three-dimensional thermomechanical asperity contact model, it was found that the coating abrasiveness was controlled by the actual micro-scale contact conditions. This study supports the classic Greenwood–Williamson model, which states that the number of micro-scale contacts and the total actual area of contact remains constant for a given load.