The effect of temperature on water desorption and oxide formation in MoS2 coatings and its impact on tribological properties

Abstract

Molybdenum disulfide (MoS2) is used extensively in aerospace applications, where liquid lubricants are not suitable. MoS2 has excellent tribological properties in vacuum, however, further research is required to fully understand the mechanisms taking place when exposed to varying temperatures in ambient atmosphere due to storage and on-ground testing. MoS2 coatings were deposited on AISI 440C steel substrates, friction and wear tests were conducted at increasing temperatures, up to 75 °C, determining the effect of temperature on wear mechanisms in air. It was found that the detected surface oxides do not impact tribological properties in MoS2 at temperatures around 75 °C. The water molecules at room temperature hinder the alignment of MoS2 layers leaving some active edge sites exposed to contacting surfaces, leading to high friction and wear. Desorption of water molecules promote parallel alignment of layers, reducing shear strength, friction and wear.