Study On Electrochemical Corrosion Behavior Of Dental ZrTi Alloys

Oral is a complex electrolyte environment. Acid material, produced by acidic diet and bacterial metabolism, and fluorine ion brought from caries prevention agent、preventive polishing and toothpaste with fluoride have adverse effects on the corrosion resistance of the metal. Titanium and its alloys, are widely used in prosthodontics due to its low density, light weight, low elastic modulus, high strength, good corrosion resistance and biocompatibility. However, titanium’s high melting point, the proportion of light, poor flowability and poor wear resistance, and due to oxidation at high temperatures, resulting in poor castability. Implants will produce loose and failure due to wear and tear after long-term use.To solve the above problems, this study adopts the alloying method. The biological element Zr is used as the matrix, Ti as a second component to decrease the melting point of the alloy and improve the castability of the alloy. Adding Ag, Cu as third element to further improve the corrosion resistance of the alloy. While, using thermal oxidation improve the corrosion resistance of the alloy by oxidation coating. The experiment using electrochemical methods measure polarization curves and electrochemical impedance spectroscopy of different components ZrTi alloys at different pH value and different concentrations of fluoride ion in artificial saliva. Combined with optical microscopy, scanning electron microscopy, analyze the influence of the alloy composition, fluoride ion concentration, pH value and oxidation coating on the corrosion resistance of the alloys.The results show that the corrosion potential (Ecorr), the corrosion current density (Icorr), resistors of passive layer (Rp1) of the same composition alloys in neutral, acidic and neutral with0.1%sodium fluoride artificial saliva solutions are no significant difference. But in acid with0.1%sodium fluoride artificial saliva solution, the Ecorr and Rp1decreasing obviously, the Icorr increasing, the corrosion resistance is on the decline. In neutral, acidic and neutral with0.1%sodium fluoride artificial saliva solutions, the Ecorr, Icorr and Rp1of different composition ZrTi alloys have no significant difference. But the corrosion resistance of various alloys has a big difference in acid with0.1%sodium fluoride artificial saliva solution. Contrast with other alloys, Zr40Ti6Ag and Zr40Ti2Cu alloys have a more positive Ecorr, and the Icorr is smaller. The Rp1is10～100times larger than other alloys. And Zr40Ti6Ag and Zr40Ti2Cu alloys always exhibited higher the pitting corrosion potential. In short, the changes of corrosion resistance of Zr40Ti6Ag and Zr40Ti2Cu alloys are small in the different corrosion environments, and the corrosion current is less than pure titanium, oxide film has a good stability and corrosion resistance.On the surface Zr40Ti, Zr20Ti alloys,10μm thick oxide coating is formed after the thermal oxidation in the air. In acid with0.1%sodium fluoride artificial saliva solution, the Ecorr of0-0.1V and the Rp1of105Ω·cm2are significantly higher than-0.2V、104Ω·cm2of Zr40Ti6Ag, Zr40Ti2Cu alloys, the Icon of102nA/cm2correspond with that of Zr40Ti6Ag, Zr40Ti2Cu alloys and the pitting corrosion potential of1.OV or so is little higher than0.8V of the Zr40Ti6Ag, Zr40Ti2Cu alloys. Alloy corrosion resistance is improved obviously after oxidation.Analysis:either hydrogen ions or fluorine ions in the corrosion solution have no apparent influence on the corrosion resistance of the alloys, but when both of them exist in the corrosion solution can reduce the corrosion resistance of the alloys, increasing the corrosion tendency of the alloys and speeding up the corrosion; Hydrogen ions and fluorine ions have small influence on the corrosion resistance of Zr40Ti6Ag, Zr40Ti2Cu alloys, so the corrosion resistance of Zr40Ti6Ag, Zr40Ti2Cu alloys is superior to that of the pure titanium and other alloys; On the surface of Zr40Ti, Zr20Ti alloys after the thermal oxidation in the air form a layer of dense oxide coating, which has a good blocking effect of solution, making the corrosion resistance of it significantly higher than that of the oxide film of ZrTi alloys spontaneous formation in air.