ICMCTF 2026 Session MD1-1-MoM: Coatings and Surfaces for Medical Devices: Mechanical, Corrosion, Tribocorrosion, and Surface Processing I

Cobalt-Chromium-Molybdenum (CoCrMo) alloys have been used in various biomedical applications, including hip and knee implants, making them highly essential in orthopedics. A major concern regarding these implants is their long-term corrosion resistance, as corrosion can have a negative impact on patient health. Corrosion resistance is impacted by a variety of factors, such as the alloy’s microstructure and the environmental conditions that can affect the release of metal ions. In this study, two different microstructures of CoCrMo were tested including homogeneous and banded samples. Each microstructure was tested under three different conditions: normal, inflammatory, and infectious. To stimulate these environments, 30 g/L protein was used for normal conditions, 0.5 mM hydrogen peroxide for inflammation, and 15 μg/L LPS for infectious conditions. To test the long term effects of these conditions, 24 hour corrosion experiments were performed using a three-electrode electrochemical set up. The electrochemical testing protocol included the sequence of open circuit potential, potentiostatic run, electrochemical impedance spectroscopy, and cyclic polarization. For banded samples the experiments were run at a constant potential of -0.7V and for homogeneous samples, it was run at -0.68V. The banded structure exhibited higher current values than the homogeneous structure, indicating that CoCrMo alloys with a homogeneous microstructure have greater corrosion resistance. Furthermore, among normal, inflammatory, and infectious conditions, the inflammatory condition resulted in the greatest alloy loss (μg) for both banded and homogeneous structures. Specifically, the banded structure showed a loss of 37.53 μg, while the homogenous structure exhibited a loss of 5.69 μg, indicating inflammatory conditions have the least corrosion resistance.

This study investigates the synergistic interactions between fretting wear and electrochemical crevice corrosion in diamond-like carbon (DLC) coating systems on AISI 316L substrate under physiologically representative conditions. Particular emphasis is placed on understanding how albumin influences fretting–corrosion mechanisms, given their critical role in many engineering and biomedical environments. A combined experimental methodology is employed, integrating micro-mechanical characterisation (instrumented indentation and scratch testing) with fretting experiments employing in-situ electrochemical characterisation to assess coating durability, damage initiation, and interfacial degradation. Electrochemical techniques, including open-circuit potential monitoring, potentiodynamic polarisation, and electrochemical impedance spectroscopy, are applied in situ during fretting to capture the evolving interaction between mechanical and electrochemical degradation processes.

Fretting was replicated by applying micro-motion to the Al2O3 ball relative to the coated plate under a dead weight normal load. A maximum Hertzian contact pressure of 800 MPa was used for the tests, at a fretting displacement amplitude of 100 µm, giving a gross slip fretting regime. Each fretting test lasted 60 minutes resulting in 3600 cycles at a frequency of 1 Hz. Detailed surface and subsurface analyses using scanning electron microscopy, focused ion beam cross-sectioning, and energy-dispersive X-ray spectroscopy reveal progressive coating damage involving micro-cracking, interfacial delamination, and tribologically induced graphitisation of the DLC layer. Results demonstrate that fretting accelerates corrosion through mechanical disruption of the coating–substrate interface, while corrosion promotes further fretting damage via under-film attack and crack propagation, establishing a genuine fretting-corrosion synergy.

A mechanistic model is proposed in which mechanical defect initiation, electrochemical attack, and debris generation act in a feedback loop, driving progressive coating degradation. These insights highlight the importance of considering protein–surface interactions and combined degradation modes when designing DLC coatings for demanding fretting–corrosion service conditions in biomedical and engineering applications.