Chemical and tribological characterization of PbOMoS 2 films grown by pulsed laser deposition

Abstract

The potential of pulsed laser deposition to incorporate additives into MoS 2 films was investigated. Composite PbOMoS 2 films were grown on stainless steel substrates using the 248 nm radiation from a KrF excimer laser. The PbO:MoS 2 ratio and the substrate temperature during deposition were varied to determine the optimum conditions for producing lubricious, long-lasting coatings. X-ray photoelectron spectroscopy was used to evaluate surface chemistry while Raman spectroscopy was used to determine bulk chemistry and crystallinity. Spectroscopic data were correlated to friction and wear measurements collected from a ball-on-flat tribometer. Films deposited at 300 K were composed of amorphous MoS 2 and other MoSPbO compounds. Crystalline PbMoO 4, MoS 2, and MoO 3 were produced after the films were annealed in air at 773 K or after tribomechnical stressing. Composite films perform significantly better during tribotesting than films composed entirely of MoS 2 or PbO. In addition, composite films demonstrate the properties of “adaptive” lubricants. MoS 2 provides lubrication at room temperature; however, when the films are exposed to oxidizing environments at elevated temperature, they adapt by forming PbMoO 4. This compound has been noted to posses lubricant properties at high temperature. Thus, there is significant potential for tailoring film compositions so that the components react to produce lubricious wear debris and to provide lubrication over extended temperature ranges.