WS 2 nanoparticles – potential replacement for ZDDP and friction modifier additives

In high-pressure, high-temperature sliding contacts, WS 2 nanoadditives react with the metal substrate to generate 100+ nm chemical tribofilms with a layered structure and excellent tribological properties. The friction, wear and micromechanical properties of WS 2 tribofilms are compared with those of tribofilms formed by the zinc dialkyldithiophosphate (ZDDP) antiwear additive and ZDDP-organic friction modifier (OFM) mixture. Nanoindentation measurements showed that WS 2 generates tribofilms with higher values of hardness and Young's modulus than ZDDP and ZDDP + OFM, which explains its excellent antiwear properties. The friction performance of WS 2 surpassed that of ZDDP + OFM. The striking reduction of boundary friction is credited to the layered structure of the WS 2 tribofilm, with exfoliated/squashed WS 2 nanoparticles that fill the gaps and cover the reacted tribofilm. In view of these results, WS 2 proves to be a suitable candidate for the replacement of problematic lubricant additives currently in use.