Corrosion and corrosion-wear response of PIRAC-treated Ti-6Al-4V in a simulated body fluid

Abstract

Total hip replacement (THR) and total knee arthroplasty (TKA) are practiced throughout the world to restore painless joint function for patients suffering from disabling joint disease. To ensure the long-tenn stability of an implanted pmi, the materials and surface prope1iies such as wear and friction characteristics are particularly important. For instance, particles generated from wear, due to relative surface motion, reduce the lifetime of the joint thus creating health hazards. Corrosion can also impose and accelerate joint degradation, as the artificial prosthetic implants are exposed to human tissue and body fluids. Titanium alloys are excellent biomaterial candidates due to their advantageous properties including superior corrosion resistance and biocompatibility. However, Ti alloys do suffer from poor tribological performance, limiting their use to static structural applications. Powder Immersion Reaction Assisted Coating (PIRAC) nitriding is considered able to provide an improvement in the surface properties of titanium alloys in a cost effective manner compared to established nitriding techniques. The principle aim of this work is to study the electrochemical behaviour and corrosion-wear response of PIRAC-nitrided Ti-6Al-4V whilst comparing the results with untreated and PVD TiN Ti-6Al-4V which were used as benchmarks. The corrosion properties of untreated and nitrided Ti-6Al-4V in Ringer's solution mixed with 30 g/L Bovine Serum Albumin (BSA) simulating the physiological environment, were evaluated by Potentiodynamic testing and Electrochemical Impedance Spectroscopy (EIS). The results show that PIRAC-nitriding does not greatly affect the excellent corrosion resistance of the Ti alloy. Under all conditions (cathodic, anodic and open circuit potentials), the untreated shows a high interface impedance, owing to its highly adherent and inert passive film. Nonetheless, both untreated and nitrided samples show a high and stable polarisation resistance after 24 h of immersion as determined via the EIS modelling with an equivalent circuit. The PIRAC-nitrided alloys show a significant increase in resistance to tribocorrosion in a simulated body fluid, when compared to the untreated alloy. EIS performed after corrosion-wear testing shows that the impedance of both the untreated and treated metal/electrolyte deteriorated as a consequence of tribocorrosion.