Nanoscale characterization of corrosion mechanisms in advanced Zr/ZrxN and Zr/ZrxN+a-C:H nano-multilayer coatings for medical tools

Bio-tribological multilayer PVD coatings deposited on stainless steel substrates have been studied on multiple scales. Anodic dissolution as a precursor of the pitting corrosion mechanisms operating in layers was described. Advanced Zr/ZrxN and Zr/ZrxN+a-C:H nano-multilayer coatings with different layer thickness ratios (metallic to ceramic) were subjected to corrosion-resistant properties analysis. Materials protected by the Zr/Zr2N(1:4 ratio) + a-C:H coating exhibited the lowest corrosion resistance in the test solution because of the corrosion behaviour of this coating was controlled by the defects content, while corrosion of coatings without additional a-C:H layer was controlled by oxidation of the nitride to form an oxide over-layer. Microstructure characterization was performed on the micro, nano and atomic scales using transmission electron microscopy techniques. It allowed to described the differences of corrosion protection of applied different coatings. The possibility of the corrosion of metallic biomaterials and their contribution to biocompatibility represents the most important consideration in the selection of metals for implants or surgical tools.