Influence of Cu Grain Size on Running-in Related Phenomena

We used a single-asperity microscopic tribosystem diamond sphere/Cu sheet to investigate the relevant phenomena affecting the dynamics of friction and wear in a macroscopic system. The influence of the average grain size of the softer of two tribopartners on friction and wear was investigated in particular. The observed tribosystem experienced a natural transition during the running time, from severe plastic flow to predominating boundary lubrication. This fact was used to study the influence of poly-α-olefine base oil and fully formulated engine oil Fuchs Titan SAE 5W45 on friction and wear during severe deformation and the boundary lubrication regime. It is shown that the initial grain size has a crucial influence on wear and friction only during first sliding interactions. During the initial sliding, the grain size rapidly decreases due to plastic deformation. The grains then become uniformly equal in size in every initial situation after approximately 30 cycles. Initially larger grains result in increased friction and wear as well as higher sensitivity to the kind of lubrication.