Effects of Multi‐Scale Patterning on the Run‐In Behavior of Steel-Alumina Pairings under Lubricated Conditions

Abstract

In nature, many examples of multi-scale surfaces with outstanding tribological properties such as reduced friction and wear under dry friction and lubricated conditions can be found. To determine whether multi-scale surfaces positively affect the frictional and wear performance, tests are performed on a ball-on-disk tribometer under lubricated conditions using an additive-free poly-alpha-olefine oil under a contact pressure of around 1.29 GPa. For this purpose, stainless steel specimens (AISI 304) are modified by micro-coining (hemispherical structures with a structural depth of either 50 or 95 μm) and subsequently by direct laser interference patterning (cross-like pattern with 9 μm periodicity) to create a multi-scale pattern. The comparison of different sample states (polished reference, laser-patterned, micro-coined, and multi-scale) shows a clear influence of the fabrication technique. In terms of the multi-scale structures, the structural depth of the coarser micro-coining plays an important role. In case of lower coining depths (50 μm), the multi-scale specimens show an increased coefficient of friction compared to the purely micro-coined surfaces, whereas larger coining depths (95 μm) result in stable and lower friction values for the multi-scale patterns.