Influence of temperature on PA 6–steel contacts in the presence of an ionic liquid lubricant

In this paper we study the tribological properties of polyamide (PA 6) containing the ionic liquid 1-hexyl, 3-methyl imidazolium hexafluorophosphate (IL) as 3 wt.% additive dispersed in the polymer matrix. Pin-on-disc tests for neat PA 6 and for PA 6 + 3 wt.%IL blend discs have been carried out against AISI 52100 and AISI 316L steel pins at variable temperatures (−35, 25 and 67 °C). At these temperatures the relationship between the loss modulus and the storage modulus as determined by dynamic mechanical analysis (DMA) are the same for both PA 6 and PA 6 + 3%IL. Neat PA 6 shows a friction decrease both at high and low temperature with respect to room temperature which could be explained by the effect of thermal softening and low temperature hardening, respectively. In contrast, PA 6 + 3%IL maintains a low friction coefficient in the whole range of temperatures with values similar or even lower to that obtained when IL is used as external lubricant. Wear rates for both materials are negligible under the conditions used for variable temperature tests. Friction coefficients and wear rates under increasing normal loads and sliding distances are always lower for PA 6 + 3%IL. Surface interactions and wear mechanisms are discussed from SEM micrographs and EDS analysis.