Friction and transfer layer formation in FCC metals: Role of surface texture and roughness parameters

Surface texture influences friction and transfer layer formation during sliding. In the present investigation, three well-defined surface textures - namely unidirectional, 8-ground, and random - were employed on steel plates. Experiments were conducted by sliding pins made of FCC metals (Al, Cu and Pb) against the steel plates using an inclined pin-on-plate sliding tester. Tests were conducted at a sliding velocity of 2 mm/s in ambient conditions under both dry and lubricated conditions. The morphologies of the worn surfaces of the pins and the formation of transfer layer on the counter surfaces were observed using a scanning electron microscope. Surface roughness parameters of the plate were measured using an optical profilometer. It was observed that the transfer layer formation and the value of the friction (including adhesion and plowing components) depend primarily on texture of plate surfaces. The effect of surface texture on the friction was attributed to the variation of the plowing component of friction for different surfaces. It was also observed that among the surface roughness parameters, the mean slope of the profile, Δa, correlated best with the friction. Furthermore, dimensionless quantifiable roughness parameters were formulated to describe the degree of plowing taking place at the asperity level.