Role of Mo on tribological properties of atmospheric plasma-sprayed Mo-NiCrBSi composite coatings under dry and oil-lubricated conditions

NiCrBSi is a material widely used for preparing wear-resistant coatings. In order to study the role of molybdenum (Mo) on tribological performance under dry and oil-lubricated conditions, Mo-NiCrBSi composite coatings were prepared by atmospheric plasma spraying. The contents of Mo in the composite coatings were ranged from 5 to 30 wt.%. X-ray diffraction, optical microscopy and scanning electron microscopy were used to characterize the phase structure and surface morphology of the composite coatings. The tribological performance of the coatings was estimated by reciprocating friction tests. The worn surface was inspected by X-ray photoelectron spectroscopy and energy dispersive spectroscopy to further analyze the wear mechanism. The results showed that the 30 wt.% Mo-NiCrBSi coating exhibited an optimal tribological performance under both the dry and oil-lubricated conditions. The wear resistance of NiCrBSi coating increased when adding 30 wt.% Mo under oil-lubricated condition. It was revealed that MoO2 and MoS2 tribo-films were generated in the friction process under dry condition and oil-lubricated condition, respectively, which accounted for the excellent tribological performance of the composite coatings. (C) 2017 Elsevier B.V. All rights reserved.