Fabrication Of TiBN Solid Lubrication Coating By PIIID And Its Properties

With the rapid development of national defense equipment manufacturing industry,many mechanical compoents should be worked at high speed and temperature.Therefore,lubricating materials with good tribological properties are urgently needed.The commonly solid lubricanting materials,such as molybdenum disulfide,diamond like carbon are easily invalid under the high temperature oxidation.Hexagonal boron nitride?h-BN?has excellent antioxidant properties and can maintain low friction performance even when the temperature is up to 900°C,so it has great potential in the high temperature solid lubrication field.However,the fabrication of h-BN based coatings was mainly concentrated on powder metallurgy or laser cladding,which cannot deposite thin films on components with precise configurations.Physical or chemical vapor deposition techniques can obtain TiBN coatings also,but the BN phases in these coatings are mainly cubic BN?c-BN?,which has high hardness,excellent abrasive resistance and high friction coefficient,and cannot be used as solid lubrication films at high temperature.Because the h-BN is an insulator and cannot be ignited by an arc discharge,it can not be made as a cathode directly.In this study,the Ti-BN composite cathodes were prepared by a complex process,which included the mixing of Ti and h-BN powders,cold pressing and vacuum thermal sintering.The results showed that when the content of h-BN in the complex cathode was below 40 wt.%,the Ti-BN composite cathode possessed good conductivity.In addition,the electrical resistivity of the composite cathode increased with the content of h-BN in it,and the relative density decreased with it.The characteristics of the plasma generated by the Ti-BN composite cathodes were acquired by a plasma sampled mass spectrometer.The influences of the magnetic duct,pressure and discharge current on the plasma were obtained.The results showed that ions in the plasma were mainly composed of Ti⁺,Ti²⁺and BN⁺.Compared with the 45° magnetic duct,the ions losing rate was near 1 time larger than that in 90° magnetic one.The relationship between the ion density and pressure showed a Gauss distribution when the pressure lied between 0.1¹.0Pa.And the plasma possessed the highest density under the pressure of 0.3Pa,which benefits obtaining a high deposition rate for TiBN coatings.With the increase of the discharge currents,the density of Ti⁺ and BN⁺ ions increased also.However,when the mean discharge current exceeded 14 A,the ion densities did not increase further.In the mean time,the continuous rise of the discharge current led to an increase in quantities of the macro-particles in the arc discharge process.The TiBN nano composite coatings were prepared by using Ti-BN complex cathode and plasma immersion ion implantation and deposition technology.The results showed that the size of the nanocrystals declined with increased content of B.The fourier transform infra-red spectrometry and x-ray photoelectron spectrum results revealed that the bond structure between B-N in the coatings was mainly composed of sp² ones.The high resolution transmission electron microscopy results showed that the TiBN nano composite coatings possesed an amorphous encapsulated nanocrystalline structure,while the naonocrystal was Ti N and the amorphous phases were BN and Ti O2.Besides,a self-layered structure appeared in all TiBN nano composite coatings,in which the sizes of the nanocrystals were varied in different layers of the coatings.With the increase of BN contents,some h-BN phases appeared in the nano crystals also.The friction coefficients of all the TiBN nano composite coatings at room temperature were lower?0.1⁰.3?and decreased with increased content of BN.The coating prepared by the Ti-BN composite cathode with the BN content of 15 wt.% possessed the best wear resistance.The high temperature oxidation results indicated that the friction coefficient of the coatings were low when the temperature was below 800°C?0.2⁰.35?.When the temperature reached 800°C,although the friction coefficient kept stable,some obvious oxidation appeared on the surface of the coatings.When the temperature was increased to 1000°C,obvious collapse appeared in the TiBN coating.