Electrochemical Characteristics of a Biomedical Ti70Zr20Nb7.5Ta2.5 Refractory High Entropy Alloy in an Artificial Saliva Solution

Abstract

High entropy alloys are a new type of multi-component material with improved mechanical properties that could be useful in medical implants. The corrosion behavior of a biomedical Ti70Zr20Nb7.5Ta2.5 alloy was examined and matched with that of commercial Ti and the traditional biomaterial Ti6Al4V in artificial saliva. Moreover, the impact of different pH and concentrations of fluoride ions on the corrosion behavior of Ti70Zr20Nb7.5Ta2.5 was also investigated. The Ecorr decreases in the following order: Ti70Zr20Nb7.5Ta2.5 > Ti6Al4V > Ti. The steady-state potential of the OCP indicates that the corrosion resistance decreases in the same order: Ti70Zr20Nb7.5Ta2.5 > Ti6Al4V > Ti. The Ti70Zr20Nb7.5Ta2.5 immersed in saliva at low pH (pH 2.0) and a high fluoride ion concentration (2000 ppm) suffers from cracking and exhibits the lowest resistance to corrosion compared to the sample immersed in the saliva without and with low concentrations of fluoride ions (0–1000 ppm) and at high pH values (5.0 and 7.0). These data reveal that if the fluoride ion concentrations are enhanced or the pH falls, the alloy corrosion resistance reduces. The EIS data show that the passive layer is made up of a duplex outer and inner oxide layer and that the alloy's resistance to corrosion in fluoride-containing solutions has been significantly reduced. Additionally, the data demonstrate that a Ti70Zr20Nb7.5Ta2.5 alloy's corrosion resistance rises with increasing immersion time with and without fluoride ions. According to the X-ray photoelectron spectroscopy investigation, the protective passive oxides include TiO2, ZrO2, Nb2O5, and Ta2O5. The alloy Ti70Zr20Nb7.5Ta2.5 can be considered as a promising material suitable for usage as a biomaterial among all the materials tested in this work.