Boundary and Extreme Pressure Lubrication

Tribological behavior of steel-based cold spray composite coatings

“…Extreme pressure additives tend to react much faster on asperities than elsewhere. Nevertheless, as the lm is worn out by sliding, it remains thin on the asperities and accumulates in between [49]. This phenomenon has been observed by some authors on hypereutectic AlSi, where ZDDP et MoDTC formed a thick tribo lm in between protruding silicon crystals, thus smoothing the nal texture [63], [64].…”

“…9c) and e). The black contrast revealed by back-scattered electron images inside the craters suggests the presence of a tribo lm, formed locally by reaction of oil additives with nascent surfaces [49]. Beside these craters, polishing grooves from the original surface can still be seen on the worn track, con rming that wear was super cial.…”

“…Friction breaks the surface oxide layer, creating nascent metal surfaces. The tribo lm creation will occur about 1000 times faster on those nascent surfaces than on oxidized ones [49]. The reactions leading to tribo lm formation can occur on different steels (stainless or not) [46], but they are slower on residual carbides of highly alloyed steels as, for example, the M2 tool steel [50].…”