| Pure titanium has gained more and more attraction as substitute for hard tissue such as artificial joint because of its good mechanical and biocompatible property.However,pure titanium often leads to failure in human environment due to its poor corrosion resistance and corrosive wear resistance.In this paper,two kinds of Nb modified layer(Nb implanted sample and Nb alloyed sample)were prepared on pure titanium by ion implantation and double glow plasma surface alloying technology,and the influence of the layers on corrosion and corrosive wear behavior of pure titanium was respectively compared in Ringer's physiological solution.The microstructure,corrosion and wear performance of pure titanium were investigated when the doses of ion implantation were 5.14×1016ions/cm2,6.85×1016ions/cm2 and 8.50×1016ions/cm2.The obtained results indicated that the dose of 6.85×1016ions/cm2 showed better performance and was choosed as the process parameter of Nb implanted sample.The process parameters of Nb alloyed sample were also determined as the following:3h of holding time,36Pa of air pressure,18mm of electrode spacing,800V of source voltage and 450V of cathode voltage.The results of SEM and XRD indicated that Nb implanted sample showed convex and compact surface morphology,which was composed of single?-Ti solid solution;Nb alloyed sample showed hollow and compact surface morphology,which was composed of Nb,?-Ti and?-Ti solid solution.The nano-hardness of pure titanium was 4.68GPa;that of Nb implanted sample was 2.89GPa due to the softening of local areas;that of Nb alloyed sample was 15.99GPa.The influence of two Nb layers on the corrosion behavior of pure titanium in Ringer's physiological solution was investigated by corrosion test.The results of electrochemical impedance spectroscopy(EIS)showed that in the initial stage,pure titanium,Nb implanted sample and Nb alloyed sample were protected by a dense oxide layer;the oxide film transformed into a double layer structure with outer loose layer and inner dense layer with increasing immersion time.The charge transfer resistance of these samples at the end of immersion was 2750k?/cm2,6240k?/cm2 and19000k?/cm2,respectively.The results of immersion test showed that the main corrosion product of pure titaniuem was loose Ti6O;that of Nb implanted samples was also Ti6O with the proportion of loose oxide decreasing;and that of Nb alloyed sample was Ti6O,Ti3O and Ti O.Therefore,the Nb cations enhanced the passivation properties of pure titanium by decreasing the concentration of anion vacancies present on titanium oxide film.In summary,the corrosion resistance of pure titanium can be improved by two kinds of Nb layers,and Nb alloyed sample exhibited better corrosion resistance.The influence of two Nb layers on the corrosion and wear behavior of pure titanium in Ringer's physiological solution was investigated by corrosive wear test.The results of EIS showed that before and after corrosive wear test,the variation of charge transfer resistance of three samples was-38.11%,-44.55%and+36.27%,respectively.Hence,corrosion resistance of Nb implanted sample was more affected by the mechanical interaction when compared with Nb alloyed sample.The wear mechanisms of pure titanium were the mixture of abrasive wear,adhesive wear,oxidation wear and pitting wear.As for Nb implanted sample,the degree of abrasive wear,adhesive wear and oxidation wear increased,but the degree of pitting wear greatly decreased.The main wear mechanisms of Nb alloyed sample were slight abrasion and oxidation wear.The specific wear rate of Nb implanted sample increased to 24.8×10-4mm3N-1m-1,which was 1.35 times of that of pure titanium.The specific wear rate of Nb alloyed sample reduced to 0.9×10-4mm3N-1m-1,which was 1/19 of pure titanium.In summary,Nb implanted sample slightly reduced the wear resistance of pure titanium in Ringer's physiological solution,while Nb alloyed sample significantly improved the wear resistance of pure titanium. |
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