Versatile Superlubricity via Boronizing on Engineering Alloys: Insights into In Situ Passivation Mechanism.

Abstract

Superlubricity with a friction coefficient <0.01 holds great promise for reducing energy consumption and global CO₂ emissions. However, current numerous innovative superlubricity techniques have persisted in specific materials, inert atmosphere or nano/micro-scale conditions. Here, a versatile and universal superlubricity strategy is demonstrated for common engineering alloys under atmospheric environment, and emphasize an innovative superlubricity design principle through surface passivation. Such superlubricity behavior is achieved by employing electrochemical boronizing surface treatment combined with liquid polyol/water mixture lubricants, revealing significant advances in terms of wide adaptability to traditional and newly-emerged alloy materials, high load capacity and high-temperature resistance (≈125 °C). The atomistic simulations and experimental results demonstrate that the energy dissipation reduction and superlubricity are driven by the weak interaction between the confined lubricant molecules and ─C_xH_y-terminated passivation tribofilm, which is in situ generated by the mechanochemical reaction between the boronized layer and the liquid lubricant. The role of passivation layer on driving superlubricity is further supported by the exceptionally super-low friction coefficient (COF≈0.008) observed in octadecyltrichlorosilane (OTS) molecular layer coated surfaces. This advancement opens the door for developing industrial-scale superlubricity techniques and has the potential to accelerate their practical applications in engineering area.