Tribological behavior of the low-concentration boric acid and ZDDP lubricating oil mixtures

Zinc dithiophosphate (ZDDP)-free environmental friendly lubricating oil research studies have gained importance due to the governmental regulations over the last decade. In this study, low concentration boric acid-base oil and ZDDP-base oil mixtures were investigated with a ball on flat reciprocating tribometer to evaluate their tribological performances. The tribological performances of 1, 3, and 5% additive and base oil mixtures were evaluated at boundary lubrication condition in three main contexts including wear rates, surface tribochemistry, and friction. Results showed that there was no significant difference between boric acid and ZDDP friction coefficients. However, boric acid showed poor wear resistance when compared with ZDDP and it cannot be an alternative additive alone to ZDDPs.