Corrosion Resistance of Additively Manufactured Titanium Alloys in Physiological and Inflammatory-Simulating Environments: Ti-6al-4v Versus Ti-29nb-21zr

Abstract

Retrieval studies in the past two decades show severe corrosion of titanium and its alloys in orthopedic implants. This damage is associated with clinical failure, resulting in a need to identify new biomaterials that are load-bearing, wear-resistant, and more corrosion-resistant. Additive manufacturing (AM) can produce new metallic admixtures and alloys that may not otherwise be producible using conventional manufacturing methods. In this study, we characterize the fundamental corrosion properties of three new AM titanium materials, including Ti-6Al-4V with added 1% nano-yttria stabilized ZrO2, admix Ti-29Nb-21Zr, and pre-alloyed Ti-29Nb-21Zr. We compare these properties to conventionally and additively manufactured Ti-6Al-4V. A 0.1 M H2O2 phosphate-buffered saline (PBS) solution, simulating inflammatory conditions, significantly increased biomaterial OCP (-0.14 V vs Ag/AgCl) compared to PBS only (-0.38 V, p=0.000). During anodic polarization, Ti-6Al-4V passive current density more than doubled from 1.28*10-7 to 3.81*10-7 A/cm2 when exposed to 0.1 M H2O2. In contrast, Ti-29Nb-21Zr passive current density remained relatively unchanged, slightly increasing from 7.49*10-8 in PBS to 9.31*10-8 in 0.1M H2O2. Ti-29Nb-21Zr oxide polarization resistance (Rp) was not affected by 0.1M H2O2, maintaining a high value (1.09 *106 vs. 1.89*106 Ωcm2), while Ti-6Al-4V in 0.1 M H2O2 solution had significantly diminished Rp (4.38*106 in PBS vs. 7.24*104 Ωcm2 in H2O2). These results indicate that Ti-29Nb-21Zr has improved corrosion resistance in inflammatory simulating environments compared to Ti-6Al-4V based biomaterials.

Keywords: Ti-6Al-4V, Ti-29Nb-21Zr, Additive Manufacturing, Corrosion, biomaterial selection