Depth Dependence of Friction in Self-Lubricating Cu-Based Materials for Highly Demanding Applications

The selection of materials with high mechanical and tribological properties defines current trends in modern materials science. In this paper we investigate the use of alloying elements, such as phosphorus (P), manganese (Mn), tin (Sn), antimony (Sb) and lead (Pb), in order to improve tribological characteristics in Cu-based self-lubricating materials. Using structural (XRD, OM) and chemical (EDX, XRF, XPS) analyses we observed distinctive elemental segregation and diffusion towards the surface under mechanical pressure, driven by elevated temperatures. Additionally, we perform GDOES in order to prove the dynamics of element migration towards the surface under working conditions. The latter is very important, because new phases, such as Pb0.8Sb0.2, SnPb2O4, Pb2O, Cu3P, etc. are formed and located near the surface, which improves the tribology in situ. The role of these phases is diverse and differentiated, such as directly lowering the friction coefficient (FC) and as a consequence lowering the temperature, which under operating conditions is over 700 °C. Alloying elements also lead to improved hardness. It was found that the friction coefficient in vacuum dropped as much as 40 times and the wear at load 40 N dropped 4 times in compared the pure copper sample.