CORROSION BEHAVIOR OF ZIRCONIUM-BASED AMORPHOUS ALLOYS IN ARTIFICIAL BODY FLUID

摘要

For the application of amorphous alloys to biomaterials, the effects of chloride ion, pH, and dissolved oxygen in artificial body fluids on the corrosion behavior of Zr_(65)Al_(7.5)Ni_(10)Cu_(17.5) amorphous alloy were investigated. The surface of the alloy polarized in electrolytes with various amounts of dissolved oxygen was characterized using X-ray photoelectron spectroscopy. Also, Zr_(60)M_5Cu_(27.5) (M: alloying element) amorphous alloys were polarized in deaerated and 4%O_2 aerated solutions. The Zr_(65)Al_(7.5)Ni_(10)Cu_(17.5) amorphous alloy showed as high polarization resistance as crystalline titanium in deaerated electrolyte with pH 7.5. With the small amount of chloride ion, this alloy did not show pitting corrosion on the polarization curve. Open-circuit potential which was always lower than pitting potential was ennobled with the decrease of pH. The pitting potential was considerably ennobled by the dissolved oxygen because of the decrease of hydroxide ion and phosphate ion in the surface oxide. On the other hand, the extra oxygen retained nickel oxide in the surface film, causing the slight decrease of pitting potential. When titanium, niobium, indium, and tungsten were employed as M, the pitting potential of the Zr_(60)M_5Al_(7.5)Cu_(27.5) amorphous alloys largely increased with the dissolved oxygen. The thermodynamic stability of oxide-state of these alloying elements was high. Those indicates that the pitting corrosion resistance of the alloy possibly increased by the small amount of oxide.