Low friction nanocomposite aluminum oxide/MoS2 coatings prepared by sol-gel method

Abstract

Decreasing of friction coefficient by lubrication is an effective way to reduce the wear of interacting surfaces, however, use of conventional lubricants faces problems in extreme environments (e.g. outer space). The use of solid lubricants (e.g. molybdenum disulfide) as solid coatings, or as components of coating systems based on non triboactive matrix (e.g. oxides) can be solution. In this work, aluminum oxide ceramic coating containing dispersed molybdenum disulfide particles was formed on the substrates using sol-gel technique. Molybdenum disulfide (MoS2) powder was suspended in alumina sol and deposited by dip-coating method on the surface of 7075 Al alloy and Si wafer. The densification of coating was made during heat treatment of substrate alloy. Prepared coatings were investigated in terms of morphology, chemical composition, crystalline structure and basic tribological properties. Morphology study of the obtained coatings revealed that their nanocomposite structure consisted of MoS2 particles uniformly dispersed in aluminum oxide matrix. The coatings were homogeneous and free of cracks. EDS and GIXRD study proved high MoS2 content within coatings. Tribological investigations carried out under low humidity conditions showed very low friction coefficient of coatings against Al2O3 counterspecimen. The interaction of MoS2 particles with aluminum oxide matrix was simulated using the SCiGRESS software. The conducted analysis showed that the dispersed MoS2 could be incorporated into the amorphous structure of aluminum oxide both by physical and chemical bonding. Obtained results indicate the potential use of MoS2 containing nanocomposite coating in contact nodes operating under outer space conditions.