CPM Seminar

Special CPM seminar

Microscopic mechanisms of wear in automotive engines

Martin Dienwiebel

IAVF Antriebstechnik AG
Karlruhe

For a long service life of lubricated mechanical systems (e.g. an internal combustion engine) the wear rate has to be just a few nanometers per hour. Hence the microscopic mechanisms leading to the generation of wear particles have to take place in a surface-near volume of a few hundred nanometers thickness.

We performed pin-on-disk tribometer experiments combined with in-situ high-resolution wear monitoring. The running conditions were chosen to achieve realistic wear rates in the order of a few nm/h after running-in. A detailed analysis showed that classical abrasive wear models are failing. The contacting surface asperities are subjected to viscoplastic flow. The local energy input is high enough to raise the temperature of the asperity close to the melting point, therefore atoms in the contact zone are highly mobile. The high mobility leads to intermixing of atoms from both contacting surfaces as well as lubricant molecules. When after a few hundred nanoseconds, the asperities leave the contact they are rapidly cooled down by the surrounding oil and the mixed and unordered state is frozen in. During this process, wear particles are generated by squeezing out material from the viscous contact zone.

In the course of the running-in the surface-near volume that is strongly modified from the original bulk material, in the sense of composition, microstructure and surface morphology. As a consequence, the friction coefficient and wear resistance is changing.