Friction and wear behaviour of low-friction coatings in conventional and alternative fuels

Today low-friction PVD coatings are used regularly in combustion engines to reduce wear and energy loss due to friction. Three coatings based on transition-metal dichalcogenides and three DLC coatings were tested with respect to tribological behaviour in non-conformal sliding contact, in five conventional and alternative fuels and fuel blending components. The friction and wear proved to vary substantially between the different tested systems. The DLC coatings exhibited extremely good wear properties, but also higher friction. Contrastingly the TMD coatings showed promising friction results, but in their present forms they do not offer sufficient wear resistance in the tested severe contact situation.

► DLC coatings exhibited extremely low wear, but wore the countersurface in all tests.
► DLCs often behaved like a homogeneous group despite different hardnesses and compositions.
► TMD coatings showed promising friction results in several fuels.
► TMDs did not offer sufficient wear resistance in the tested severe contact situation.
► There are indications that important tribochemical reactions take place in several of the contacts.