Ultra-low friction of polyethylenimine / molybdenum disulfide (PEI/MoS2)15 thin films in dry nitrogen atmosphere and the effect of heat treatment. (November 2018) - Saravanan, Prabakaran
Abstract: The unique frictional behavior of polyethylenimine/molybdenum disulphide (PEI/MoS2 )n thin films on steel substrates, deposited via the layer-by-layer (LbL) technique, is explored. The effects of gaseous atmosphere (i.e. air vs. dry nitrogen), and heat treatment of the coatings are investigated. The coefficients of friction (COFs) are reduced by factors of ca. 2 and 11 in air and N2 respectively, compared to an uncoated steel substrate. Ultra-low friction (COF < 0.02) is achieved in dry N2 . After heat treatment of the coating at 500 °C, the COF in air and nitrogen does not change significantly, but the coating demonstrates much higher durability. Detailed characterization of the coating and wear debris are performed to understand the origin of these tribological properties. Highlights: Solid lubricant polyethylenimine/molybdenum disulphide (PEI/MoS2 )15 thin films on steel substrates were developed using novel LBL technique. The effects of environment (air and nitrogen), and heat treatment were investigated. Fresh coating (before heat treatment) in ambient air is quickly compromised. However, ultra-low friction (COF < 0.02) was achieved in dry N2 environment with long wear life. Remarkably, the coating was highly durable in ambient air after heat treatment at 500 °C, and ultra-low friction (COF < 0.02) was retained in dry N2 environment as well. Heat treatment transformed the MoS2 and PEI into MoO3 and amorphous carbon, respectively, formed a composite which resulted in superior tribological properties.