Hollow spherical and nanosheet-base BN nanoparticles as perspective additives to oil lubricants: Correlation between large-scale friction behavior and in situ TEM compression testing

In the present study we utilized h-BN nanoparticles (NPs) with different morphologies (hollow NPs with smooth surface (H-BNNPs), solid NPs with pompon-like or petalled structure (P-BNNPs), and globular NPs formed by numerous thin h-BN nanosheets (N-BNNPs)) as additives to PAO6 oil. Two sliding 100Cr6 surfaces were tested in the presence of PA06 + BNNP lubricants with 0.1% and 0.01% of BNNPs. The positive effect of BNNP additives increased along the row P-BNNPs -> H-BNNPs -> N-BNNPs. Utilization of N-BNNPs permitted to decrease noticeably the friction coefficient from 0.1 to 0.06 and reduce significantly the wear rate. In situ mechanical TEM tests were also performed to visualize and correlate the mechanical properties of individual h-BN NPs to their large-scale friction behavior.