Evaluation of corrosion behaviour of nickel-chromium alloy in artificial saliva

Abstract

NiCr base alloys have important applications in the fabrication of dental prostheses. One of the major requirements of these materials is their corrosion resistance in saliva. In this study, corrosion resistance of one commercially available NiCr alloy was investigated in artificial saliva. Material and methods Corrosion behavior of the NiCr alloy was studied using two techniques including potentiodynamic polarization and weight loss. In first method, the corrosion current density per mA/cm2 was calculated by the Stern-Geary equation according to polarization curves. In weight loss method, corrosion rate was measured in mil per year (mpy) scale. Surface morphology of the specimens was studied using scanning electron microscopy (SEM). In order to determine the statistical difference, one-way ANOVA and post-HOC Tukey-HSD tests were employed with a difference significance of 95%. Results Corrosion rate (mpy) was 71.953.40, 17.261.03, 8.920.35 and 6.930.54 in pH of 2.5, 5, 7 and 9, respectively. Corrosion potentials were significantly different. Corrosion current density measured in pH of 2.5 and 5 was significantly different with the rest of pH values. In addition, corrosions rates were followed the same difference as corrosion rates. However, corrosion rates in pH of 7 and 9 were not significantly different. Weight loss value obtained in pH of 2.5 was significantly different with other groups, but those obtained in pH of 5, 7 and 9 were not significantly different. Conclusion It is observed that NiCr alloy behaves differently in saliva with different pH. Corrosion resistance decreases as pH increases. In more acidic saliva, corrosion rate is higher due to the higher dissolution rate of Ni. This can be understood by the nature of weak passive film on Ni-rich phase allowing Ni to dissolve. However, the less acidic saliva leads to formation of more stable passive film on Ni and therefore the dissolution of Ni decreases leading to lower corrosion rates