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Purpose This paper aims to develop a Mini-Tribometer for in-situ observation of subsurface. Design/methodology/approach To observe the change of the microstructure during wear in real time, an in-situ observation mini-tribometer was developed according to the requirements of the basic frictional experiments and carried out the verification experiments. Findings The subsurface images and the tribological data obtained from the mini-tribometer clearly show that the graphite in the matrix moves to the surface and takes part in lubrication mainly in the form of extrusion and peeling off, and the migration of graphite in the copper-based composite to the frictional interface to act as lubricant and to result in the decrease of the friction coefficient. The experimental results of the developed tribometer are accurate, which can provide important references for further research on the wear mechanism of materials. Originality/value The developed in-situ observation mini-tribometer can be used to observe the dynamic wear mechanism of the frictional pairs, which is very important for optimization of material design and tribological performances.

To further reveal the mechanism of graphite migration in copper based graphite composites sliding against 45 steel, the particle Flow Code in 2 Dimensions (PFC2D) was employed to simulate and analysis the relationship between internal force chain and graphite migration in the composites. The simulation results show that a migrated graphite particle layer is formed on the composite surface during friction, and maintains dynamic equilibrium relying on “self-consumption”. The graphite migration displacement to the friction surface is affected by the force chain. The greater the force chain strength is, the smaller the graphite migration displacement is. When the force chain angle is in the range of 75° to 95°, the migration of the graphite particles can not occur; when the angle is 95° to 135°, the graphite migration displacement increases with the increase of the angle. And the greater force chain strength corresponds to the less worn particles and the less migrated graphite particles. The simulation results are significant for optimizing material design and improving the friction performances of copper based graphite composites.

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