A comparative study on microstructure and tribological characteristics of Mo2FeB2/WC self-lubricating composite coatings with addition of WS2, MoS2, and h-BN

Abstract

To enhance the tribological properties and service life of Mo2FeB2/WC coatings, self-lubricating composite coatings with addition of WS2, MoS2, and h-BN were fabricated using laser cladding. The morphology, microstructure, microhardness, and tribological properties of the Mo2FeB2/WC self-lubricating composite coatings were investigated. The results indicated that the addition of WS2, MoS2, and h-BN increased the bonding properties between the coating and substrate. Sulfides and nitrides were found in the self-lubricating composite coatings; the Mo2FeB2/WC/h-BN coating exhibited a fine dendritic structure. The microhardnesses of the Mo2FeB2/WC, Mo2FeB2/WC/WS2, Mo2FeB2/WC/MoS2, and Mo2FeB2/WC/h-BN coatings were 1591.3 HV0.5, 1345.6 HV0.5, 1378.9 HV0.5, and 1415.3 HV0.5, respectively. After the addition of WS2, MoS2, and h-BN, the coefficients of friction decreased by 9.09%, 15.15%, and 30.30%, respectively; the corresponding wear rates decreased by 10.80%, 19.03%, and 30.97%, respectively. The self-lubricating phases significantly improved the tribological properties of the Mo2FeB2/WC coating. The main wear mechanisms of the Mo2FeB2/WC coating were adhesive and mild oxidative wear; the wear mechanisms after the addition of WS2, MoS2, and h-BN were abrasive and oxidative wear. The wear debris was powder-like for the Mo2FeB2/WC/WS2 and Mo2FeB2/WC/MoS2 coatings and flake-like for the Mo2FeB2/WC/h-BN coating. The lubricating transfer film caused an improvement in the tribological properties.