Investigation on the Tribological Properties of FeS, Cu2S, MoS2, and WS2 Sulfide Films Under Water Lubrication

FeS, MoS2, WS2, and Cu2S solid films were prepared on CoCrFeNiMo high entropy alloy (HEA), and their tribological performance was tested under water lubrication. The results show that the MoS2/CoCrFeNiMo and the Cu2S/CoCrFeNiMo composite coatings provided excellent tribological properties. The MoS2 film of the MoS2/CoCrFeNiMo composite coating was not worn through at the load of 2 N, providing a reduction of 86% of friction coefficient (μ = 0.03) and 69% of the wear rate (2.68 (Formula presented.) 10−9 cm3/Nm), compared to CoCrFeNiMo coating. At a higher applied load, the anti-wear performance of MoS2 film deteriorated because the MoS2 reacted with oxygen and water to form α-MoO3. α-MoO3 hinders the sliding between layers of MoS2, increasing the third-body abrasive wear of the CoCrFeNiMo coating. Unlike the MoS2/CoCrFeNiMo composite coating, the Cu2S/CoCrFeNiMo composite coating exhibited an improved friction coefficient and wear rate at all loads. This performance is a result of Cu2S reacting with oxygen and water to form Cu and CuO, protecting the CoCrFeNiMo coating from severe wear.