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

Abstract

Boron carbide (B 4 C) 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.

Effects of lubrication and humidity on the abrasiveness of a thin boron carbide coating

“…The average coating abrasiveness versus the number of ball-on-disc cycles is plotted on a log-log scale in figure 1 for both the lubricated and dry sliding conditions. In agreement with previous findings of the B 4 C coating under dry sliding conditions [3][4][5][6][7][8], the average coating abrasiveness decreased with increasing sliding distance following a power law scaling relationship for both the lubricated and dry cases. Because of the linear relationships present in the coating abrasiveness results of figure 1, it can be shown [9] that the instantaneous coating abrasiveness A n at any given cycle n is given by…”

“…The abrasiveness of a thin B 4 C coating sliding against 52100 bearing steel under dry conditions has extensively been studied by Harris et al [3] and Siniawski et al [4][5][6][7][8] using a ball-on-disc machine. From these studies, it was observed that the B 4 C coating polished the steel ball counterpart relatively quickly, in approximately 30 cycles of abrasive wear at a sliding velocity of 10 cm/s under a 100 g load.…”

“…Furthermore, it was also determined that the sliding conditions, namely the sliding speed and applied nominal load, do not influence the coating abrasiveness [11]. Furthermore, Siniawski et al determined that the overall coating thickness does not influence the coating abrasiveness slope [6]. However, Siniawski et al have found some key parameters that do affect the coating abrasiveness, such as the counterpart roughness [6] and the counterpart tempering temperature [8].…”

“…Furthermore, Siniawski et al determined that the overall coating thickness does not influence the coating abrasiveness slope [6]. However, Siniawski et al have found some key parameters that do affect the coating abrasiveness, such as the counterpart roughness [6] and the counterpart tempering temperature [8]. Furthermore, Siniawski et al determined that the coating abrasiveness is independent of the nominal contact conditions.…”

“…Furthermore, Siniawski et al determined that the coating abrasiveness is independent of the nominal contact conditions. Rather, it was proposed that the coating abrasiveness is directly dependent upon the micro-scale asperity contact conditions [6]. Since all of these previous studies have been performed under dry sliding conditions, it is necessary to investigate the effects of lubrication and humidity on the coating abrasiveness.…”