| Titanium alloy has the advantages of low density,high specific strength and good biocompatibility.It is widely used in aerospace,petrochemical and biological medicine.However,the surface hardness of titanium alloy is not high enough,and the weakness of toughness,easy wear and corrosion resistance limit the further expansion of its application scope.Therefore,the application of surface modification technology to improve the surface performance of titanium alloy has significant theoretical research value and wide application prospect.Metal ceramic as a kind of high hardness materials,it can be deposition on the surface of the matrix by a certain method under the premise of keeping the shape and size of substrate,and it can effectively improve the wear resistance of matrix,the mechanical properties,corrosion resistance and service life,etc.With the rapid development of surface engineering technology,the preparation technology of high-performance surface coating has been gradually enriched and the application field has been expanded.In this paper,a NbC coating was synthesized on the surface of TC4 alloy by double-cathode plasma sputtering deposition technique,the Nb was deposited on the surface of the substrate at first,and then the Nb and C were deposited concurrently.The microstructure was characterized by scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS).The mechanical properties were tested by scratch test,nano-pressure test and friction wear test.The corrosion behavior of the coating was studied by means of open circuit potential,tafel curve and electrochemical impedance spectroscopy,in a 3.5wt.% NaCl solution under the room temperature.The results of the above test are as follow:(1)The XRD test results show that the coating composition is NbC and C,and it had the(110)crystal surface preferred orientation.The SEM observed that the coating thickness was almost 5 μm,and the coating tissue was dense,which was good in combination with the matrix,the surface of NbC coating was smooth,with no obvious holes,shedding and cracks.EDS analysis of main elements in the coating is Nb and C.(2)The scratch test indicated that the critical load value of the coating is 101.35 N,which proves that the bonding with the matrix can meet the work requirements.In the ductile test,the coating did not induce the microcrack of outward expansion,and the nano pressure test indicated that hardness and elastic modulus of coating reached 23.5Gpa and 260.7Gpa.Room temperature and high temperature friction and wear experimental results show that the coating has a lower friction coefficient and wear volume,SEM observation found that the grinding crack of coating is more smooth than that of matrix,and less micro crack and spalling,shows that the NbC coating improved the wear properties of the matrix.(3)In a 3.5 wt.%NaCl solution at room temperature,electrochemical corrosion experiment found that NbC coating initiative open circuit potential higher than that of matrix,and the time of achieving the stable less than substrate,showed that the coating surface more easily than the matrix form passivation film.The polarization curve test results show that NbC coating has lower corrosion current density,higher corrosion potential and higher polarization resistance.Impedance spectroscopy testing showed that NbC show greater charge transfer resistance and higher impedance modulus than TC4 matrix,prove NbC coating has lower corrosion rate,formed the high stable passivation film in the process of corrosion.In summary,NbC coating can be used in the titanium alloy surface strengthening because better mechanical properties and corrosion resistance. |
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