Study On The Performance Of The Nb Coating On Titanium Alloy Deposited By Double Cathode Plasma Sputtering Technique

With the vigorous development of social economy and technology,the global population is gradually aging.At the same time,some degenerative orthopedic diseases are gradually becoming younger and the incidence is increasing.Not only that,in recent years,the demand for orthopedic implant materials has grown with the incidence of sports injuries,traffic accidents and work accidents increasing.Titanium alloys have the advantages of low density,high specific strength,excellent corrosion resistance and biocompatibility.Therefore,they are often used as biological implant materials.But some of the harmful elements in titanium alloys may harm human health or cause implant failure,leading to some serious consequences such as secondary surgery.In this subject,a double cathode plasma sputtering deposition technique was used to deposit a Nb coating on the surface of Ti–6Al–4V alloy,and the mechanical performance and electrochemical properties of the coating were studied.The phase composition,cross-section morphology,element distribution and the composition of the passive film on the coating surface were characterized by XRD,SEM,XPS and other characterization methods.The hardness of the coating was evaluated by the Vickers microhardness method.And the binding force between the coating and TC4 substrate was tested by scratch method.In addition,a variety of electrochemical analysis methods were used to study the electrochemical performance of the Nb coating,pure Nb and the Ti–6Al–4V substrate in 0.9wt% NaCl and Ringer's solutions at 37±0.5? for simulating human body fluid environment.The main conclusions are as follows:(1)The surface of the deposited Nb coating is uniform and dense without obvious defects.The coating is well bonded to the TC4 substrate,with a thickness of about 18 ?m.According to point-scan spectrum,line-scan curve and element distribution map of the crosssection for the Nb coating,the coating possesses a high purity.According to XPS analysis,the main component of the passive film of the Nb coating is Nb2O5.(2)The average Vickers hardness of the Nb coating is 1643.12 HV,which is higher than the TC4 substrate.There is no microcrack defect around the coating indentation under the stress superimposed field,indicating that the coating shows a higher fracture toughness.Through the scratch test,the critical load(Lc)of the Nb coating is 104.65N>30N,which can fulfil the engineering application requirements of sliding contact.(3)According to the open-circuit potential and potentiodynamic polarization curve results of the Nb coating,pure Nb and Ti–6Al–4V alloy in 0.9wt% NaCl and Ringer's solutions at 37±0.5?,the Nb coating has the highest open-circuit potential,self-corrosion potential and polarization resistance,with lowest self-corrosion current density.In the EIS test,the Nb coating show the highest low-frequency modulus impedance(|Z|f?0)and the widest phase angle platform.As the immersion time increasing,the corrosion resistance of the coating is the most stable,and the corrosion resistance of TC4 substrate is obviously decreased after soaking for 72 h.In the Mott–Schottky analysis,the thickness of the passive film of the Nb coating is the largest,and the Nb coating shows the lowest flat band potential and donor density.Its diffusion coefficient is second only to pure Nb.These results demonstrated that the Nb coating possesses the best electrochemical stability and corrosion resistance.