| Friction and wear in industrial manufacturing cause huge national economic losses,application of protective coatings to mechanical components is an effective solution to enhance operation efficiency and engine duration.As a class of ultra-hard,light-weight materials,AlMgB14-based boron-rich borides have aroused widespread attention for their promising mechanical and tribological properties.In particular,the hardness of AIMgBi4-TiB2 reaches the maximum hardness value over 40GPa,second only to diamonds and c-BN.Tribological studies on AlMgB14-TiB2 coatings demonstrated that AlMgB14-TiB2 coating significantly reduced the coefficient of friction and exhibited high wear resisitance under both water-glycol and mineral oil lubrication conditions.In addition,AlMgB14-TiB2 coatings have excellent high temperature stability and chemical stability,which can satisfy high requirements of protective coatings in high-tech areas.Therefore,the development of new AlMgB14-TiB2 coatings fabrication technology and in-depth study of tribological characteristics of AlMgB14-TiB2 coatings has great significance to promote both practical application and industrial production.In this paper,the Al-Mg-Ti-B coatings were deposited by High power impulsed magnetron sputtering(HiPIMS)without external substrate heating.During the deposition process,the bias voltages of OV to-150V were applied to the substrate to attract the ions towards the growing coatings and control the kinetic energy of ion bombardment.X-ray diffraction(XRD),scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),and nano indentation tests were carried out to analyze the effect of bias voltage on the structure,composition and mechanical properties of the Al-Mg-Ti-B coatings.The Al-Mg-Ti-B coatings deposited under different bias voltages all had a dense amorphous structure.With the bias voltage increasing from 0V to-150V,the mechanical properties of the coatings were improved continuously,which can be ascribed to the reduced B-O content caused by re-sputtering effect under higher bias voltage condition.The nano-hardnesses and the elastic moduli of Al-Mg-Ti-B coatings were 28?37GPa and 315-348GPa,respectively.Tribological characteristics of Al-Mg-Ti-B coatings prepared by HiPIMS were further investigated in this paper.The tribological behaviors of Al-Mg-Ti-B coatings deposited under different bias conditions were tested by using UMT-3 friction tester with PAO+MoDTC as lubricants.The results showed that all the coatings were subjected to a low friction period during the friction process,but the friction coefficients increased with the extension of the test time.The coefficients of friction(COF)of the 0?-100V coating were about 0.05?0.08,while the minimum coefficient of friction of-150V coating was 0.065 and then grew to more than 0.1.The XPS results implied that the MoDTC decomposed to form a layered low shear MoS2 tribo-film between the tribo-pairs which contributed to low friction.The Mo can be further oxidized to MoO3 by heat generated in friction process to increase the friction coefficient.However,Mo and S was not detected on the surface of the friction pair of the-150V coating,which can be attributed to the hardness of this coating.The steel ball rubbed against-150V Al-Mg-Ti-B coatings subjected to severe worn,no tribo-film was expected to survive for the rapid materal loss on contact surface.In this paper,the influence of annealing temperature on tribological behaviors of Al-Mg-Ti-B coatings lubricated by MoDTC was also studied.The value of COF increased as the annealing temperature increased.The XPS results showed that the content of MoS2 decreased and that of MoO3 increased in friction film with the annealing temperature increased,which can exacerbate abrasive wear between tribo-pairs.Besides,the coatings suffered different annealing treatment formed the distinct oxides on the surfaces of the coatings,and the content of rutile phase increased with the annealing temperature.It was speculated that anatase and rutile could affect the tribological behaviors of the Al-Mg-Ti-B coatings by affecting the adsorption of the friction film on surface of coatings. |
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