Rich activated edges of hexagonal boron nitride flakes in-situ triggered by nickel nanoparticles to achieve efficient reduction of friction and wear

The application of hexagonal boron nitride (h-BN) nanosheets as lubrication additives has attracted tremendous attention due to their excellent stability and friction performance. However, the exfoliation and functionalization of h-BN nanosheets are difficult which appear to limit the practical application of them. Herein, we demonstrate that commercial h-BN flakes (h-BNFs) can be directly used to fabricate antifriction and antiwear coatings through a simple spraying process after mixing with nickel nanoparticles (Ni NPs). The experiment results and density functional theory calculations demonstrated that Ni NPs could in-situ promote nitrogen atoms to break down from the edges of h-BNFs, forming electron deficient h-BNFs and Ni NPs, and then the electron deficient Ni NPs would adsorb oxygen to generate superoxide radicals during friction process. The as-obtained superoxide radicals can react with the electron deficient h-BNFs, and these functionalized h-BNFs can stably adsorb poly-alpha-olefins (PAO6) molecules to form antifriction and antiwear tribo-films on the stainless steel (SS) substrates. Besides, the metal-edge interaction (SMEI) between Ni NPs and h-BNFs can accelerate PAO6 molecules converting into carbon based films on the counterpart. Fantastically, the antifriction and antiwear performance of SS have been greatly improved after coated by Ni/h-BNF composite coatings with PAO6, with friction coefficients (COFs) as low as 0.07 and wear rates less than 1.5 × 10−13 m3/(N·m), respectively. This finding opens up a new way for the practical application of commercial h-BNFs as low friction lubricants.