The role of transfer layer on the tribological characteristics of silver-coated surfaces

The tribological role of transfer layer was studied with silver coatings under various ranges of load and sliding speed. Silver coatings were performed with thermal evaporation, ion beam assisted deposition and functionally gradient coating method. Tests were performed in dry sliding conditions, using a ball-on-disk contact configuration, at the load of 0.02–17.64 N and the sliding speed of 20–1000 mm/s. Optical microscope and electron probe micro analyzer analyses showed that contact surfaces were covered with the transfer layers of agglomerated wear particles depending upon the contact conditions, and they greatly influenced the tribological characteristics of the surfaces. However, the formation of transfer layer was suppressed as the sliding speed increased above a critical sliding speed, and no transfer layer was able to form. For building up a general framework of tribological behavior of the silver coating films, all test data were summarized on a map whose axes are contact pressure and sliding speed.