Bi 2 S 3 is a promising solid lubricant for demanding applications, such as oil extraction, heavy mining, and aerospace components. However, so far its tribological behavior has not been studied in depth. Bi 2 S 3 soft coatings were evaluated utilizing reciprocating sliding tests under different levels of relative humidity level, contact stress, and sliding speed and the results were benchmarked against MoS 2 coatings. In addition, ab initio calculations using density functional theory modeling were employed for studying the interaction between the sul des and the steel substrates and the effect of water intercalation at an atomic level. It was found that Bi 2 S 3 presents excellent environmental adaptability and substrate protection over a wide range of testing conditions, thanks to its characteristic crystal structure.
The present work investigates the friction and wear properties of composite Bi2S3 -MoS2 soft coatings under different humidity levels. To achieve this goal, suspensions containing different proportions of Bi2S3 and MoS2 were sprayed onto polished SAE 1010 steel substrates to generate soft lubricating coatings. The coatings were subjected to reciprocant sliding tribological tests in air at different humidity levels, between 20 and 80%. Additionally, the formation of tribofilms in dry conditions was evaluated by means of reciprocant tests with increasing total sliding distances. The resulting wear surfaces were analyzed using SEM-EDS, Raman microspectroscopy, and laser confocal microscopy. The frictional behavior of the composite coatings was more stable than that of neat ones. The addition of Bi2S3 to MoS2 greatly Tribological performance of Bi 2 S 3 /MoS 2 composite coatings enhanced the durability of the coatings at all the tested humidity levels, reaching up to a 760% increase in their durabilities. This effect depended on the humidity level and the ratio between Bi2S3 and MoS2.
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