Bi2S3 and MoS2 Soft Coatings: A Comparative Study of Their Frictional Behavior Under Different Humidity Levels, Normal Loads, and Sliding Speeds

Abstract

Bi2S3 is a promising solid lubricant for demanding applications, such as oil extraction, heavy mining, and aerospace components. However, its tribological behavior has not been studied in depth. Burnished Bi2S3 soft coatings were evaluated utilizing reciprocating sliding tests under different levels of relative humidity level, normal load, and sliding speed and the results were benchmarked against MoS2 coatings. In addition, ab initio calculations using density functional theory modeling were employed for studying the interaction between the sulfides and the steel substrates and the effect of water intercalation at an atomic level. It was found that Bi2S3 coatings present excellent environmental adaptability and substrate protection over a wide range of testing conditions, thanks to their characteristic crystal structure.