Estudo da nitretação a plasma da liga TI6AL4V ELI para aplicação ortopédica

Abstract

Titanium-made intra-corporeal implants are still a significant portion of arthroplasty metallic components, due to excellent biocompatibility and low allergenic and toxic features. However, surface modifications are of paramount importance for such applications, aiming performance improvement. In this work, plasma nitriding of Ti6Al4V in a hollow cathode setting was statistically evaluated by varying different times and temperatures of process and assessing the resulting surfaces. All surfaces showed a micro-scale layer, containing titanium nitrides. The nitrided disks showed increased wettability, roughness and hardness, due to the nitrogen penetration into the substrates. An optimal point for plasma nitriding at 940 °C for 3 hours was achieved. Wear and corrosion tests were carried out to evaluate the tailored surface in comparison to the pristine samples. A significant improvement in wear was observed, with a wear coefficient about thrice smaller than the original one, due to the hardened, ceramic-like compound layer. The corrosion tests outcome points to a surface responding slightly worse in a body fluid solution, but not enough to make it bioincompatible. Biological assays showed that the nitrided surface is not toxic, according to ISO standardized in vitro cytotoxic analysis and cell adhesion tests through L929 mouse fibroblast cell lines. Cell proliferation decreased over the treated samples, in part due to modifications on micro-grooved surface and its hydrophilic character.