Thermodynamic Structural Stability and Polarization Behavior of Cast Amorphous Alloy

The thermodynamic structural stability and anodic polarization behavior in Hanks' solution of cast amorphous Zr₆₅Al_7.5Ni ₁₀Cu_17.5 alloy rods with a diameter of 2.0 mm and 2.5 mm and a length of 35 mm were evaluated. The change of the magnitude of the super-cooled liquid region owing to structural relaxation was obtained from the differential scanning calorimetry (DSC) curve. Since the super-cooled liquid region of the distant region from the sprue of mold was larger than that of the proximate region to the sprue, the structural stability was lower in the distant region than in the proximate region. It was revealed that the structural stability varies along the distance from the sprue. In electrochemical analysis in a simulated body fluid, the specimens sampled from the distant region showed higher open-circuit potential, lower passive current density, and lower pitting potential than those from the proximate region. In other words, the amorphous structure with low stability shows higher passivity but lower pitting corrosion resistance than that with high stability. Consequently, the corrosion behavior of zirconium-based amorphous alloy sensitively depends on the structural stability in a biological environment.