Macroscale ultradurable superlubricity on passivated transition-metal diborides

Abstract

Superlubricity is a sliding regime with almost vanishing friction sustained under stringent material conditions. This remarkable phenomenon was first found between surfaces with incommensurate lattice structures, and later extended to materials with weak shear, as in many two-dimensional layered materials. Such materials, however, face great challenges that limit their applications, including the difficulty to scale up to meet the needs of many practical implementations and low durability stemming from the intrinsic structural weakness. Overcoming these limitations hinges on new design and fabrication of advanced superlubricating materials. Here, we report on the realization of macroscale ultradurable superlubricity on passivated transition-metal diborides (TMB2) following an unconventional design principle that first construct materials with strong anti-wear ability then create superlubricity via effective surface passivation. TMB2 possess superior mechanical strength and durability, along with the ability to activate in-situ load-induced passivation layers via tribochemical actions at the surface. The resultant passivated TMB2 exhibits characteristic superlubricating and ultradurable friction coefficient (0.002) and wear rate (10−19 m3/N·m). These findings introduce a fresh approach toward rational design and implementation of superlubricating materials, opening a new avenue for versatile applications at large (up to industrial) scales.