Oxide degradation precedes additively manufactured Ti‐6Al‐4V selective dissolution: An unsupervised machine learning correlation of impedance and dissolution compared to Ti‐29Nb‐21Zr

Abstract

AbstractAdditively manufactured (AM) Ti‐6Al‐4V devices are implanted with increasing frequency. While registry data report short‐term success, a gap persists in our understanding of long‐term AM Ti‐6Al‐4V corrosion behavior. Retrieval studies document β phase selective dissolution on conventionally manufactured Ti‐6Al‐4V devices. Researchers reproduce this damage in vitro by combining negative potentials (cathodic activation) and inflammatory simulating solutions (H2O2‐phosphate buffered saline). In this study, we investigate the effects of these adverse electrochemical conditions on AM Ti‐6Al‐4V impedance and selective dissolution. We hypothesize that cathodic activation and H2O2 solution will degrade the oxide, promoting corrosion. First, we characterized AM Ti‐6Al‐4V samples before and after a 48 h −0.4 V hold in 0.1 M H2O2/phosphate buffered saline. Next, we acquired nearfield electrochemical impedance spectroscopy (EIS) data. Finally, we captured micrographs and EIS during dissolution. Throughout, we used AM Ti‐29Nb‐21Zr as a comparison. After 48 h, AM Ti‐6Al‐4V selectively dissolved. Ti‐29Nb‐21Zr visually corroded less. Structural changes at the AM Ti‐6Al‐4V oxide interface manifested as property changes to the impedance. After dissolution, the log‐adjusted constant phase element (CPE) parameter, Q, significantly increased from −4.75 to −3.84 (Scm−2(s)α) (p = .000). The CPE exponent, α, significantly decreased from .90 to .84 (p = .000). Next, we documented a systematic decrease in oxide polarization resistance before pit nucleation and growth. Last, using k‐means clustering, we established a structure–property relationship between impedance and the surface's dissolution state. These results suggest that AM Ti‐6Al‐4V may be susceptible to in vivo crevice corrosion within modular taper junctions.