Corrosion protection of AZ31B magnesium alloy using Ti-Zr thin films for biodegradable implant applications

Biodegradable Mg alloys are attractive for temporary orthopedic implants because they can resorb in vivo, potentially eliminating the need for removal surgeries and reducing stress shielding due to their bone-like elastic modulus. However, clinical adoption is limited by rapid, non-uniform degradation that can compromise mechanical integrity, cause hydrogen gas evolution, and result in insufficient bioactivity for osseointegration. One effective strategy to address these limitations is the use of dense, adherent Ti–Zr-based thin films that serve as barrier/interfacial layers while preserving biocompatibility. In this context, we obtained Ti–Zr–X coatings (X = Cu, Nb, or CuNb) on AZ31B substrates (15 mm in diameter, 2 mm thick) by using unfiltered cathodic arc evaporation. Coating deposition was carried out at room temperature by using a substrate bias of −100 V and an Ar flow of 20 sccm, with composition-specific cathode currents and deposition times. Prior to corrosion-based investigations, structural and microstructural analyses were conducted to confirm the intended elemental composition. SEM observations revealed dense and homogeneous surfaces, while GIXRD results indicated a mixed crystalline microstructure for all Ti-based coatings, consisting of hexagonal TiZr, as well as tetragonal TiCu and/or cubic TiNb phases. Potentiodynamic measurements showed that the corrosion response strongly depends on coating chemistry, with the TiZrNb coating exhibiting the highest improvement in corrosion resistance among all investigated systems. This behavior was further supported by electrochemical impedance spectroscopy results, which revealed higher polarization resistance and more stable behavior for TiZrNb, indicating enhanced barrier properties and improved protection of the AZ31B substrate.

This work was supported by the Romanian Ministry of Research, Innovation and Digitization through CCCDI–UEFISCDI, project no. PN-IV-P7-7.1-PTE-2024-0618 and PN-IV-P8-8.3-PM-RO-TR-2024-0065, within PNCDI IV, as well as through the National Research Development and Innovation Plan 2022–2027, Core Program, Project no: PN 23 05, contract no. PN11N-03-01-2023.