Exploring low friction of lubricated DLC coatings in no-wear conditions with a new relaxation tribometer

• DLC coated surfaces are tested using an original tribometer, called the relaxation tribometer.
• This technique evaluates the transient friction at zero speedand the viscous damping friction.
• Some information on the film thickness can be extracted.
• The electrical resistance contact measurement determines the lubricant regime.
• The relaxation tribometer results are not comparable with those of classical tribometers.

The friction behavior of ta-C and a-C:H as DLC coatings is investigated using a new method. Two green lubricants were used: oleic acid and glycerol. This technique is able to measure with a great accuracy, without any force transducer, two contributions of friction. The first one, μ0μ0 is the transient friction coefficient at zero speed (which differs from the static and dynamic friction coefficient at constant speed) and the second one, μ1μ1 is a velocity-dependent friction coefficient. This work aims to investigate the different friction contributions for steel/steel, steel/DLC and DLC/DLC contacts. Moreover, the results are compared with a conventional reciprocating cylinder-on-plane tribometer working at constant sliding speed. Overall, the results show the superiority of the ta-C/ta-C combination in reducing μ0μ0.