Selective transfer phenomenon in lubricated sliding surfaces with copper and its alloy coatings made by electro-pulse spraying

The decrease of the coefficient of friction and wear are characteristics of the selective transfer phenomenon caused by the self-formation of a non-oxidising metal film in the friction zone. In this paper, the possibility of providing the selective transfer phenomenon by electro-pulse spraying (EPS) will be discussed. The analysed copper and brass coatings were manufactured by an electric pulse at 5 kV and an energy density of about 4.7-5 MJ/kg. EPS manufactured coatings have a fine-grained, multi-layer structure with a small share of voids and non-metal inclusions. The analysis (tribological test, microscopy) of such conditioned friction pairings has shown that a protecting metal film will be formed by itself, even at marginal lubricated test conditions. As a consequence, a low coefficient of friction (f = 0.003-0.004) occurs in the contact zone, which is similar to those, which indicate viscous friction.