O-to-N atom substitution in h-BN impedes its interlayer slip in humid environments

Abstract

The remarkable structure and chemical diversity of hexagonal boron nitride (h-BN) make it suitable as an excellent solid lubrication, particularly in humid and high-temperature environments. However, owing to the complex interplay between the phase transition, defect formation, and heteroatom doping in h-BN during the macroscale friction process, it remains a significant challenge to understand the dominant factor for reducing/worsening friction. In this study, the intrinsically low-friction characteristic of h-BN in humid environments is explored by altering its initial surface atomic conformation through plasma pretreatment. This involves the direct introduction of oxygen atoms (Argon/Oxygen plasma), the locking of nitrogen atoms (Hydrogen plasma), or the supply of additional nitrogen atoms (Nitrogen plasma). This strategy efficiently elucidated the dominant interfacial interaction between water molecules and h-BN for low friction and wear, which lies in the capacity to effectively adsorb water molecules to form a nanostructured water layer, subsequently promoting interlayer slip. Conversely, oxygen doping, nitrogen locking, and supplying reduced the aggregation of water molecules at the h-BN interlayer, causing different degrees of increase in friction force. The targeted modulation of h-BN offers a theoretical foundation for recognizing its low-friction nature and provides comprehensive guidance for antifriction design in humid environments.