Microstructure and tribological behavior of plasma sprayed NiCrAlY/WC-Co/cenosphere/solid lubricants composite coatings

Abstract

Present investigation deal with NiCrAlY/WC-Co/Cenosphere/MoS<inf>2</inf>/CaF<inf>2</inf>, NiCrAlY/WC-Co/Cenosphere/MoS<inf>2</inf>/CaSO<inf>4</inf> and NiCrAlY/WC-Co/Cenosphere coatings deposited on MDN 321 steel using atmospheric plasma spraying. Tribological properties of MDN 321 steel and coatings are evaluated from room temperature (RT) to 600 °C under dry lubrication conditions using a pin on disc high-temperature tribometer. Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and Energy Dispersive Spectroscopy (EDS) are used to characterize the coatings. Presence of cenospheres in these coatings might effectively reduce wear acting as localized regions accumulating wear debris. The result shows that wear rate of all the coatings are lower as compared to MDN 321 substrate at all the test conditions. NiCrAlY/WC-Co/Cenosphere/MoS<inf>2</inf>/CaF<inf>2</inf> and NiCrAlY/WC-Co/Cenosphere/MoS/CaSO<inf>4</inf> coatings registered lower friction coefficient as compared to NiCrAlY/WC-Co/Cenosphere coating and MDN 321 substrate. Characterization of the NiCrAlY/WC-Co/Cenosphere/MoS<inf>2</inf>/CaF<inf>2</inf> and NiCrAlY/WC-Co/Cenosphere/MoS<inf>2</inf>/CaSO<inf>4</inf> coatings worn out surface suggests that MoS<inf>2</inf> provides lubrication at 200 °C and formation of CaMoO<inf>4</inf>, MoO<inf>3</inf> through tribo chemistry reaction at higher temperature provides lubrication at 600 °C. SEM micrograph of worn surface demonstrates that the main wear mechanism is plowing and delamination. © 2018 Elsevier B.V.