Effect of Surface Chemistry on the Mechanisms and Governing Laws of Friction and Wear.

Recent studies have shown that interface chemistry, that is, the formation and breaking of chemical bonds across contacting interfaces, is closely related to the wear and friction behavior at the nanoscale. In reality, the dangling bond density (DBD) at contacting surfaces can vary greatly. Currently, it remains unclear how friction and wear mechanisms depend on DBDs and whether the Archard's law for wear and Amonton's law for friction are still applicable for contacting surfaces with different DBDs. In this work, we address these issues by studying the wear and friction behavior between two sliding diamond-like carbon surfaces by controlling DBDs via hydrogenation using molecular dynamics simulations. It is found that the chemical bond breaking and remaking across the contacting interface play the key role in determining the friction and wear behavior. During the sliding, a higher DBD leads to more chemical bond formations across the interface, causing stronger wear via either atom or cluster detachments. With the same DBD, a mechanism transition from an atom-by-atom to cluster detachments is observed by increasing the normal load. Remarkably, a fully saturated surface can exhibit a wearless friction. We further show that after necessary modifications, the Archard's law for wear and the Amonton's law for friction may be applicable at the nanoscale. The present work reveals insights into the effect of interface chemistry on the friction and wear, and it provides guidelines for effective antiwear design.