Galvanic Corrosion among Ti–6Al–4V ELI Alloy, Co–Cr–Mo Alloy, 316L-Type Stainless Steel, and Zr–1Mo Alloy for Orthopedic Implants

In orthopedics, occasionally, different types of metals are used in applications in which they are in contact with each other. However, few studies have electrochemically investigated the galvanic corrosion of orthopedic implants formed of different metals. In this study, galvanic corrosion of Ti–6Al–4V ELI alloy, Co–Cr–Mo alloy, and 316L type stainless steel, which are used in orthopedics, and a newly developed Zr–1Mo alloy as a low-magnetic susceptibility material was evaluated in saline. Coupling of the Ti–6Al–4V ELI and Co–Cr–Mo alloys did not exhibit localized corrosion and maintained highly stable passive films. Coupling of the 316L type stainless steel and Co–Cr–Mo alloy, temporary localized corrosion occurred. Similarly, coupling of the Zr–1Mo and Co–Cr–Mo alloys, temporary localized corrosion occurred. However, both of 316L type stainless steel and Zr–1Mo alloy were finally repassivated spontaneously with the immersion time. The degree of the localized corrosion of the Zr–1Mo alloy was smaller than that of 316L type stainless steel. No galvanic current was observed when the Ti–6Al–4V ELI and Co–Cr–Mo alloys were coupled. A slight galvanic current flowed when 316L type stainless steel or the Zr–1Mo alloy was coupled with the other alloys; however, the galvanic current with the Zr–1Mo alloy coupling recovered to zero after a certain period owing to repassivation. No metal ions were detected from the couplings with Zr–1Mo.