Corrosion Analysis of PMEDM-Modified Ti6Al4V Surfaces: Insights from Potentiodynamic Measurements, Ion Release, KPFM and Crevice Corrosion Evaluation

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Abstract
It has been shown that the incorporation of silver into the surface of a titanium alloy (Ti6Al4V) by powder mixed electrical discharge machining (PMEDM) exhibits an antiadhesive effect against Staphylococcus spp.. This study aims to investigate the electrochemical performance of this modified surface under simulated physiological conditions, mimicking in vivo corrosion-inducing conditions. Electrochemical behavior was analyzed using potentiodynamic polarization measurements, Kelvin probe fore microscope (KPFM) measurements and ion release quantification, while crevice-corrosion mechanisms were evaluated retrospectively by scanning electron microscopy and energy-dispersive X-ray spectroscopy.Corrosion current density showed an inverse association with PMEDM discharge energy, while neither silver content in the modified zone nor the open-circuit potential exhibited a significant association with corrosion activity. Crevice exposure led to Ti-rich, O-poor deposits at the inner end consistent with hydride formation and localized Ag-associated microgalvanic pitting corrosion were observed; which could be confirmed by local Volta potential differences in KPFM measurements. However, no widespread material degradation or propagating crevice corrosion was observed under the investigated conditions. Metal quantification revealed higher absolute release of alloying elements from the rougher PMEDM surfaces and an increase in the Ag release with the Ag content on the surface; the measured released Ag levels were within ranges regarded as antibacterial.Together, these findings indicate that PMEDM processing parameters influence the global electrochemical response, whereas Ag (particles) primarily affect localized surface mechanisms and Ag ion release. Under the investigated conditions, no correlation between Ag and corrosion current nor widespread surface degradation was detected, which could be translated into independent adaptation options for both electrochemical performance (based on discharge energy) and antibacterial properties (based on Ag content).

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