The running-in corridor of lubricated metal–metal contacts

• Testing the running-in behavior of systems with ultra-low wear rates.
• Running-in corridors as energetic entity to describe the tribological system.
• Formation of the third body as response to the energetic stressing conditions.
• Optimization of tribological systems based on the corridor concept.

In this paper the question is raised whether the coefficient of friction and the wear rate of a lubricated metal–metal system after passing the running-in can be deduced from the initial friction power density this tribological system was subjected to. This contribution defines a running-in corridor as specific energetic range in which the tribological system is able to develop ultra-low wear rates and small coefficients of friction. It will be shown that this corridor is associated with the formation of the third-body. The running-in corridor has a certain width which depends on external tribological stressing conditions, on materials, lubricants and mainly on the initial coefficient of friction. Using two different material pairings it will be demonstrated how tribological systems can be taught to find the route into the running-in corridor. Furthermore, levers of optimization employing friction-modifying additives or appropriate final machining routines will be discussed. The results of this contribution help to improve the understanding of ultra-low-wear systems. In addition comprehensive support for tribological optimization is given.