Hydrophobicity And Tribological Properties Of WC-CoCr Textured Coatings Prepared By HVOF Spraying

It is urgent to improve the anti-adhesion and wear resistance of the PDC bit when developing the technology of nonconventional energy exploration.The HVOF-sprayed WC-CoCr coatings are suitable for strengthening the steel body of drill bit,due to its excellent wear resistance,corrosion resistance and good bonding strength.But it needs to improve its hydrophobic properties.In this study,a WC-CoCr cermet coating with thickness of 200 ?m was prepared by HVOF spraying,and the surface of the coating was modified by laser surface texturing.The cross-sectional of the coating was observed by scanning electron microscopy(SEM).The 3D morphologies of the textured coatings were observed by the white light profiler.The wettability and tribological properties were tested by contact angle test and friction test,and the following conclusions were obtained:(1)The increase of surface roughness can lead to an increase in the hydrophobicity of the surface.The contact angle CA has a positive relationship with the roughness Sa,and the contact angle changes from hydrophilic to hydrophobic.In terms of tribological performance,the larger the surface roughness,the larger the friction coefficient,but the difference is not obvious.As the surface roughness of the coating increases,the surface wear volume decreases slightly.Oxidation occurs during the friction process,and adhesive wear occurs.(2)The hydrophobic properties of the surface treated by the laser texturing were significantly improved,the CA of the grid texture with a distance of 100 ?m was the largest,and it had a significant anti-friction effect under dry friction condition.The CAs of the deionized water and the drilling fluid reached up to 136.5° and 112.2° after the laser texture treatment on the polished coating.The texture coverage ratio R increases with the decrease of the texture spacing,and the CAs increases with the increase of texture coverage due to the combined effect of changes in surface morphology and chemical composition.But the hydrophobicity of the textured coating is not stable.The friction coefficient of each texture increases with the spacing increases under dry friction.In the same spacing,the friction coefficients of grids,grooves and pits increase in turn.Under drilling fluid lubrication,the friction coefficient of the three textures were greater than that of the original surface.The wear mechanism under dry friction is mainly adhesive wear and oxidation wear.Under the lubrication of the drilling fluid,three-body wear occurs.(3)The grid textures modified with fluorosilane showed good hydrophobic properties and anti-friction performance.The corresponding CAs increases with the increase of R,and all the modified surfaces show hydrophobic properties.The CAs of the texture with distance of 40 ?m and width of 100 ?m with deionized water and drilling fluid reached up to 138.22 ° and 125.5 °,respectively.The measured CAs of the deionized water with the modified surface are very close to the theoretical value of ?c of the Cassie model.The results of the friction test under drilling fluid lubrication show that when the width or spacing of the texture is the same,the greater the R,the smaller the friction coefficient,and it is basically smaller than that of the polished coating.However,the wear volume increases with the increase of R.Three-body wear occurs.