Enhanced growth of ZDDP-based tribofilms on laser-interference patterned cylinder roller bearings

Abstract

Laser surface texturing has been successfully applied in the past to various machine elements in order to improve their tribological performance. In this study, direct laser interference patterning was used to produce periodic cross-like surface patterns on commercial cylinder roller bearings. The wear behavior of as-patterned bearings was studied by a modified FE8 test rig under boundary lubrication. A mineral oil (ISO VG 100) as a base oil additivated with 0.02 wt % zinc dialkyldithiophosphate (ZDDP) was used for the tribological tests which were performed under a Hertzian pressure of 1.92 GPa and maintained at 80 °C and 20 rpm for 2 h. The laser-patterned bearings showed a significantly reduced mass loss by two orders of magnitude compared to the unpatterned reference bearings. A closer look at the samples proved the formation of the characteristic blue-colored ZDDP tribofilm on top of the laser-induced topography maximum positions. Due to the higher contact pressure at the laser-induced peaks, the tribofilm formation was preferable at those positions thus protecting against wear. The laser patterns nearly remained unworn compared to the reference samples. A subsequent Raman analysis of the laser-patterned bearings clearly revealed the formation of zinc and iron sulfides as well as phosphates at the peak points.