Microstructure,Tribological And Electrochemical Properties Of Cr-B-C-N Coatings In Aqueous Environment

Cr?B?CN coatings and Cr?Ti??B?N coatings were prepared on Si?100?wafers and 316 L disks by using closed-filed magnetron sputtering system,and the crystallite phases and bonding structures of coatings were characterized by X-ray diffraction?XRD?and X-ray photoelectron spectroscopy?XPS?,respectively.The surface and cross-sectional profiles of coatings were analyzed by scanning electron microscopy?SEM?.The hardness and elastic modulus of coatings were measured by a nano-indentation tester,while the adhesion strength of coatings to the substrates was analyzed by acoustic emission scratch tester.The tribological properties of Cr?B?CN coatings and Cr?Ti??B?N coatings were tested in water environment by ball-on-disk tribometer,and the wear tracks on coatings were analyzed by optical microscope and non-contact three dimensional profilometer.To further investigate the wear mechanism of coatings in water environment,the wear tracks on coatings were analyzed by SEM quipped with Energy Dispersive Spectroscopy?EDS?.The electrochemical properties of coatings in seawater were investigated by conventional three electrode cell,and the open circuit potential tests?OCP?,electrochemical impendence spectroscopy?EIS?tests and anodic polarization measurements were conducted?1)The CrBCN coatings with different B concentrations were prepared by adjusting CrB₂ target current,and incorporated B mainly existed as soft amorphous BN phases.When the CrB₂ target current varied in the range of 0-3 A,the hardness of Cr-B-C-N coatings fluctuated around 18 GPa,but the CrBCN-3 coatings' elastic modulus decreased to 231±4.89 GPa.With further increasing the CrB₂ target current to 4 A,the hardness and elastic modulus of coatings both decreased slightly.When Cr?B?CN coatings slid against SiC balls in tap water,CrBCN-3 coatings displayed the superior tribological properties due to the great mechanical properties and the lubrication effects of Si?OH?₄ gels and H₃BO₃ with lamellar structure on the sliding interface.2)CrN,CrTiN and CrTiBN coatings were prepared by using closed-field magnetron sputtering system,and CrN coatings mainly consisted of CrN nanograins,and incorporated Ti and B elements mainly existed as TiN_0.3 nanograins and amorphous BN phases in CrTiN and CrTiBN coatings.When three kinds of coatings slid against SiC and Si₃N₄ balls in deionized water separately,CrN coating displayed relatively better tribological properties due to the superior mechanical properties and higher adhesion strength to substrates.When three coatings slid against Al₂O₃ ball in deionized water,CrN behaved the best friction and wear properties.When three coatings slid against SUS440 C ball,CrTiBN coatings displayed best tribological performance among three coatings due to the formation of lubrication film of H₃BO₃ and the relatively lower hardness of SUS440 C ball.3)The electrochemical properties of Cr?B?CN coatings and Cr?Ti??B?N coatings in seawater were measure by conventional three electrode cell,and the results indicated that the corrosion resistance of CrBCN coatings increased with the increasing CrB₂ target current due to the more compact structure and few structure defects like cracks and pinholes,which could play a pole in inhibiting the penetration of seawater to substrates.Similarly,compared to CrN and CrTiN coatings,CrTiBN coatings also showed the best electrochemical performance due to the improved compactness of coatings' structure and fewer deposition defects like cracks and pinholes.4)When Cr?B?CN coatings slid against SiC balls in seawater,CrBCN-1 and CrBCN-3 coatings displayer lower friction coefficient and wear rate due to the lubrication effects of Si?OH?₄ gels and H₃BO₃ with lamellar structure on the sliding interface.When the friction tests of CrBCN-3 coatings sliding against SiC balls at different loads and velocities were tested in seawater separately,delaminations were occurred on the wear tracks of coatings tested at higher loads due to the inadequate adhesion strength,while the tribological performance of CrBCN-3 coatings was improved a lot at higher sliding velocity,which was attributed to the formation of water film.The comparison of tribological performances of CrBCN-3 coatings sliding against SiC,Si₃N₄,Al₂O₃ and SUS440 C balls was also conducted in seawater,and the CrBCN-3/SiC tribopair displayed the best tribological performance.