Browsing by Author "Mouele, Emile S. Massima"

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    Corrosion improvement of 304l stainless steel by zrsin and zrsi(N,o) mono-and double-layers prepared by reactive cathodic arc evaporation
    (MDPI, 2021) Dinu, Mihaela; Parau, Anca Constantina; Kiss, Adrian Emil; Mouele, Emile S. Massima
    Zr-based nitrides and oxynitrides were deposited by reactive cathodic arc evaporation in monolayer and double-layer structures with the aim of increasing the corrosion protection of 304L stainless steel (SS) in a biomedical aggressive environment. All coatings had a total thickness of 1.2 m. Compared to the bare substrate, the surface roughness of the coated samples was higher, the presence of microdroplets being revealed by scanning electron micrography (SEM). The X-ray diffraction investigation of the ZrN phases revealed that the peaks shifted towards lower Bragg angles and the lattice constants increased as a result of Si and O2 inclusion in ZrN lattice, and of the ion bombardment characteristic of the cathodic arc method, augmented by the applied bias substrate. SS/ZrSiN/ZrSi(N,O) showed the best corrosion performance in an acidic environment (0.9% NaCl and 6% H2O2; pH = 4), which was ascribed to the blocking effect of the interfaces, which acted as a corrosion barrier for the electrolyte ingress. Moreover, the aforementioned bilayer had the highest amount of Si and O in the composition of the top layer, forming a stable passive layer with beneficial effects on corrosion protection.
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    In vitro corrosion of titanium nitride and oxynitride-based biocompatible coatings deposited on stainless steel
    (MPDI, 2020) Pana, Iulian; Braic, Viorel; Mouele, Emile S. Massima
    The reactive cathodic arc deposition technique was used to produce Ti nitride and oxynitride coatings on 304 stainless steel substrates (SS). Both mono (SS/TiN, SS/TiNO) and bilayer coatings (SS/TiN/TiNO and SS/TiNO/TiN) were investigated in terms of elemental and phase composition, microstructure, grain size, morphology, and roughness. The corrosion behavior in a solution consisting of 0.10 M NaCl + 1.96 M H2O2 was evaluated, aiming for biomedical applications. The results showed that the coatings were compact, homogeneously deposited on the substrate, and displaying rough surfaces. The XRD analysis indicated that both mono and bilayer coatings showed only cubic phases with (111) and (222) preferred orientations. The highest crystallinity was shown by the SS/TiN coating, as indicated also by the largest grain size of 23.8 nm, which progressively decreased to 16.3 nm for the SS/TiNO monolayer. The oxynitride layers exhibited the best in vitro corrosion resistance either as a monolayer or as a top layer in the bilayer structure, making them a good candidate for implant applications.