Environmental Impact on Crystallization of MoS2 Composites Under Pressure and Shear

Molybdenum disulfide (MoS2) coatings are a popular option for lubrication in aerospace and hermetic applications due to low friction/wear in dry environments. Infrequent exposure to humid environments or testing in terrestrial atmospheres can negatively impact the performance and structure of pure MoS2 coatings, necessitating the use of dopants to counteract degradation. Composite MoS2 coatings commonly utilize dopants like Ti, C, Cr, Ni, Sb2O3, Pb or Au, many of which have shown improved performance over un-doped MoS2 coatings leading to the adoption of a variety of composite formulations across industrial applications. This work focuses on the widely used MoS2-Sb2O3-Au coatings and their anomalously high friction behavior (µ > 1) in humid environments at nominal contact pressures (~ 0.5 to 1 GPa) without coating failure. The origin of these high friction deviations is investigated using high-throughput tribological testing in environments with varying contact pressure and humidity. The Sb2O3 and Au composition is varied to understand the role of dopants in promoting high and low friction sliding interfaces. The results from this work suggest that increasing dopant concentration, like increasing water concentration or reducing contact pressure, is another source for inhibition of MoS2 recrystallization in the sliding contact leading to abrasive, high friction interfaces.