Sub-Micro Laser Modifications of Tribological Surfaces

In order to address necessary improvements and optimizations of actual highly stressed tribological systems, their overall energy efficiency must be increased through the deployment of pinpointed surface solutions. For this purpose, not only wear, but also the friction behavior of these tribological systems has to be improved. Lubricants and greases are widely used in the industry to reduce adequately the friction and wear of a wide range of tribological systems, but for certain systems, they possess some drawbacks (reduced cleanliness, limited working temperatures, etc.). Therefore, alternative solutions such as laser texturing, which can modify the lubricant dynamics and the materials surface properties, offer new possibilities to decrease the friction and improve the wear properties of tribological systems. In the present study, channel and nanostructured ripple structures (also known as laser induced periodic surface structures or LIPSS) were produced, using an ultra-short pulse laser on mirrorpolished 42CrMo4 discs, and characterized. The LIPSS distinguish themselves from the channel structure through their waveform with amplitude smaller than 1 lm. In order to investigate the effects of such surface structures on the overall tribological performance, oscillating wear tests (120 N, 90 degrees C, 25 Hz, 4 mm, 2 h) with a SRV4-Tribometer using polished 100Cr6 convex cylinders as counter bodies were performed. The results obtained from these investigations with the 2 different surface structures were compared with a benchmark system (surfaces without structures). The tribological investigations showed that the nanostructured LIPSS tested against anti-friction coated cylinders significantly reduced the friction coefficient by a factor of 25 % in comparison to the benchmark, without influencing negatively the wear behavior.