Guiding lubricant on stainless steel surfaces by channel-like structures fabricated by roller- and micro-coining

Guiding lubricant back to the tribological contact or preventing lubricant migration out of the contact zone can be considered as an efficient approach to significantly reduce friction and wear in machine components. This paper aims at studying the spreading behavior of an additive-free lubricant (PAO 4) on coined stainless steel surfaces (AISI 304) under the effect of a controlled temperature gradient of 2 °C/mm. Single channels and multi-channel samples were manufactured by roller coining and hot micro-coining, respectively. A systematic study of the influence of the geometrical parameters on the resulting spreading behavior has been performed. For polished reference samples, a preferential oil spreading parallel to the temperature gradient was observed which can be correlated with Marangoni forces. For single channels, the spreading velocity increases with an increase in structural depth. Multi-channels show a pronounced anisotropic spreading behavior. Lubricant migration towards the colder side of the sample can be prevented if the structures are oriented perpendicular to the temperature gradient. For multi-channel surfaces, the spreading behavior parallel to the temperature gradient is greatly influenced by the periodicity and area density. Samples with a smaller periodicity and greater area density show a higher spreading velocity of a droplet.