Interfacial Bonding Controls Friction in Diamond–Rock Contacts

Abstract

Understanding friction at diamond–rock interfaces is crucial to increase the energy efficiency of drilling operations. Harder rocks usually are usually more difficult to drill; however, poor performance is often observed for polycrystalline diamond compact (PDC) bits on soft calcite-containing rocks, such as limestone. Using macroscale tribometer experiments with a diamond tip, we show that soft limestone rock (mostly calcite) gives much higher friction coefficients compared to hard granite (mostly quartz) in both humid air and aqueous environments. To uncover the physicochemical mechanisms that lead to higher kinetic friction at the diamond–calcite interface, we employ nonequilibrium molecular dynamics simulations (NEMD) with newly developed reactive force field (ReaxFF) parameters. In the NEMD simulations, higher friction coefficients are observed for calcite than quartz when water molecules are included at the diamond–rock interface. We show that the higher friction in water-lubricated diamond–calcite than diamond–quartz contacts is due to increased interfacial bonding in the former. For diamond–calcite, the interfacial bonds mostly form through chemisorbed water molecules trapped between the tip and the substrate, while mainly direct tip–surface bonds form inside diamond–quartz contacts. For both rock types, the rate of interfacial bond formation increases exponentially with pressure, which is indicative of a stress-augmented thermally activated process. The friction force is shown to be linearly dependent on the number of interfacial bonds during steady-state sliding. The agreement between the friction behavior observed in the NEMD simulations and tribometer experiments suggests that interfacial bonding also controls diamond–rock friction at the macroscale. We anticipate that the improved fundamental understanding provided by this study will assist in the development of bit materials and coatings to minimize friction by reducing diamond–rock interfacial bonding.

Frictional Aging of Single‐Asperity Nanoindentation Contacts in Quartz and Calcite

“…During the hold period in our experiments the contacts slip roughly 40 nm (in the 1‐s holds) to 200 nm (in the 1000‐s holds), which suggests that if the bond‐formation rate is similar to the calculations by Bhamra et al. (2021) then interfacial C‐O bonds will form at the same rate as the contact area growth rate ($$\dot{A}$$). Bhamra et al.…”

“…They find that C‐O bonds form directly between diamond and quartz and diamond and calcite, along with C‐O‐Ca, C‐H‐O bridging bonds in the presence of humidity (25%–30%). The number of bonds increases over the first 0.2–2 nm of slip (depending on their simulated slip rate) after which the number of bonds remains approximately constant (Bhamra et al., 2021). During the hold period in our experiments the contacts slip roughly 40 nm (in the 1‐s holds) to 200 nm (in the 1000‐s holds), which suggests that if the bond‐formation rate is similar to the calculations by Bhamra et al.…”

Development and application of ReaxFF methodology for understanding the chemical dynamics of metal carbonates in aqueous solutions

“…34 Another study was to understand the physicochemical mechanism at the rock-calcite interface due to friction. 35…”

A review of recent advances and applications of machine learning in tribology

“…From 1996 to 2022, several studies have investigated the different shear-thinning behaviors of a number of small molecules using the everevolving techniques of NEMD simulations. 293,[300][301][302][303][304][305] Dini and collaborators have used NEMD simulations to study nanotribology, [306][307][308][309][310][311][312] including, to investigate the mechanochemistry of phosphate esters confined within sliding iron surfaces, 313 and to derive the transient-time correlation function (TTCF) expression for the computation of shear stress and slip velocity. 314 More details regarding the use of NEMD simulations in tribological applications can be found in several articles available in the literature.…”