Effect of Reinforcement Phases on the Electrochemical Behavior of (TiB+TiC)/Ti-6Al-4V Composites in Passivating Solution

Abstract (TiB+TiC)/Ti-6Al-4V composites consist of Ti-6Al-4V matrix material reinforced with TiB whiskers and TiC particles, offering significant potential for applications in the aerospace and automotive industries. However, the incorporation of reinforcement phases enhances the mechanical properties of the matrix but inevitably affects its electrochemical passivation-dissolution properties. In this study, the influence mechanisms of reinforcement phases on the electrochemical behavior of (TiB+TiC)/Ti-6Al-4V in passivating NaNO3 solution were thoroughly investigated. The results reveal that at high current densities, reinforcement phases detach as the surrounding matrix dissolves under the flushing action of the solution, thereby markedly enhancing the uniformity of the surface dissolution morphology during electrochemical machining. Simultaneously, the reinforcement phases also increase the porosity of the passive film formed on the (TiB+TiC)/Ti-6Al-4V surface, rendering it susceptible to breakdown under low current density conditions. This results in severe stray current corrosion on the machined surface. Based on these findings, an electrochemical passivation-dissolution model was established for (TiB+TiC)/Ti-6Al-4V in NaNO3 solution. Finally, a (TiB+TiC)/Ti-6Al-4V stepped structure was successfully fabricated with high efficiency, excellent precision, and good surface quality by employing an efficient and precise continuous electrochemical mill-grinding method using the same tool and solution.