Effects of Thickness and Roughness Variations on the Abrasiveness of a Thin Boron Carbide Coating

Abstract

Boron carbide (B 4 C) is well known for its high hardness and favorable wear resistant properties. In dry sliding wear contact, it polishes its mating surface and provides fatigue resistance to coated parts. Employing such run-in coatings demands a thorough understanding of the parameters which directly influence the changes that occur in the coating abrasiveness during the polishing process. In this study, the effects of the overall coating thickness, overall coating roughness, substrate roughness and substrate roughness orientation are examined in connection with abrasiveness. The coating thickness only influences the initial abrasiveness, whereas the coating roughness drastically affects the rate at which the abrasiveness decreases. Finally, no significant changes are observed in the abrasiveness due to substrate roughness or substrate roughness orientation effects. This work provides further insight into the design of a finite-life run-in coating.

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

“…The average coating abrasiveness was obtained using Equation 2 for the various macro-scale contact conditions, namely ball-, pin-and cone-on-disc, and is plotted versus the number of ball-on-disc cycles on a log-log scale in figure 2. In agreement with the previous findings by Harris et al [3,8,9] and Siniawski et al [4][5][6], the average abrasiveness of the coating, for all of the macro-scale contact conditions, decreased with increasing sliding distance following a power law scaling relationship. Because of the linear relationships shown in figure 2, it can be shown [8] that the instantaneous coating abrasiveness A n during the nth cycle is given by…”

“…It should be noted that all of the abrasiveness results were obtained using a constant load of 10 g, or approximately 0.1 N. A study by Harris et al [10] has indicated that the slope of the coating abrasiveness is independent of load after a certain number of cycles, except for very low loads. We also observed similar trends by comparing the slope of the ball-on-disc experiments performed using a 10 g load with our previous results from ball-on-disc experiments performed using a 100 g [3][4][5][6]8]. Although a slight shift in the initial coating abrasiveness was observed as the load was changed, a similar slope was observed irregardless of the applied load.…”

“…The abrasiveness obtained for the pin-ondisc macro-scale contact condition, while considering its misalignment, decreased at a faster rate because the pin is always sliding over the same B 4 C coating surface. A direct relationship between the average coating abrasiveness and the sharpness of the coating asperities, measured by either the asperity angle of attack or the asperity radius of curvature, was previously established by Siniawski et al [5,6]. The asperities that provided the polishing of the steel pin counterpart were affected more severely, which accounted for the sharper decrease in the effective average coating abrasiveness.…”

“…Our previous work [3][4][5][6] has supported the idea of a finite-life run-in coating whose abrasiveness corresponds to an optimal period of polishing. After the very brief optimal period of polishing, the abrasiveness of the finite-life coating would ideally decrease to zero, providing no additional abrasion.…”

“…The changes in the abrasiveness of a thin B 4 C coating during dry sliding wear has extensively been studied by Harris et al [3] and Siniawski et al [4][5][6]. In these studies, a B 4 C coated disc was slid against an AISI E 52100 steel ball using a ball-on-disc machine.…”