ABSTRACT
The purpose of the study was to ascertain the corrosion resistance in Hanks' solution of Cr-Ni-Mo stainless steel (AISI 316L) coated with diamond-like carbon (DLC) coatings to establish its suitability for biomedical applications, e.g., as temporary implants. The influence of the carbon coating thickness as well as the correlated effect of the metallic sublayer type and defects present in DLC films on corrosion propagation were discussed. The results obtained were compared with findings on the adhesion of DLC to the steel substrate. The synthesis of carbon thin films with Cr and Ti adhesive sublayers was performed using a combined DC and a high-power-impulse vacuum-arc process. Evaluation of the corrosion resistance was carried out by means of potentiodynamic polarisation tests and scanning electron microscopy. Adhesive properties of the sublayer/DLC coating systems were measured using a scratch tester. It was found that systems with Ti sublayers were less susceptible to the corrosion processes, particularly to pitting. The best anti-corrosion properties were obtained by merging Ti with a DLC coating with a thickness equal to 0.5 µm. The protective properties of the Cr/DLC systems were independent of the carbon coating thickness. On the other hand, the DLC coatings with the Cr sublayer showed better adhesion to the substrate.
ABSTRACT
The asymmetric unit of the title compound, C(34)H(30)N(2)O(4), contains four independent half-mol-ecules, the complete mol-ecules being generated by inversion symmetry. The mol-ecules each have planar (within 4σ) perylene-tetra-carb-oxy-lic diimide fragments with bent side chains. In one of the independent mol-ecules, each 3-pentyl fragment is disordered over two conformations in a 7:3 ratio. In the crystal, π-π inter-actions link mol-ecules into stacks propagated in [010]. The crystal packing also exhibits weak inter-molecular C-Hâ¯O hydrogen bonds.
ABSTRACT
The current market requirements are related to the introduction of new protective coatings for tools and machine parts with much better performance properties. These requirements are met by the AlCrSiN coatings; however, knowledge on the adhesion of these coatings to the substrate, as well as on their corrosion resistance, is deficient. The article presents the results of technological works on the coating deposition from AlCrSi cathodes with a silicon concentration from 0 at% to 10 at% by the cathodic arc evaporation and the results of systematic studies of their structure, mechanical, tribological and electrochemical properties. A correlation between the above-mentioned properties and the silicon concentration in the AlCrSiN coatings has been found and discussed. The coatings formed from cathodes containing less than 5 at% Si crystallize in the cubic structure. The size of the crystallites decreases with the silicon concentration increase. The coatings are characterized by a high hardness with a maximum of about 37 GPa (2 at% Si). The adhesion of the coatings is almost independent of the concentration of silicon. The wear rate is about one order of magnitude higher for coatings deposited from cathodes with a silicon concentration of 5 at% and 10 at% compared to a coating with a lower silicon concentration. This finding is consistent with the results of corrosion resistance studies. The coating deposited from the cathode with 10 at% of silicon exhibits the best anticorrosion properties against the salt solution.
ABSTRACT
PURPOSE: The endoprostheses made of cobalt-chromium-molybdenum (Co-Cr-Mo) alloys belong to the group of the most popular metallic implants used for reconstruction of hip joints. For such biomaterials, the primary goal is a correct and long-term functioning in the aggressive environment of body fluids. Therefore, the purpose of this study was to examine both the morphology and the corrosion resistance of implants made of the cobalt alloy used in Birmingham Hip Resurfacing (BHR) system (Smith & Nephew). For comparative purposes, the electrochemical studies were done for the nitrided stainless steel - Orthinox. METHODS: Observations of the microstructure of the material under investigation were performed by means of the optical metallographic microscope and the scanning electron microscope. Furthermore, Energy Dispersive X-ray Spectroscopy was used to analyse the chemical composition of the endoprosthesis. Characterisation and evaluation of electrochemical corrosion resistance of the selected alloys were performed by potentiodynamic polarisation tests. RESULTS: The structural studies confirmed that Co-Cr-Mo (BHR system) is characterised by a typical dendritic microstructure with carbide precipitates, mainly M23C6, within the interdendritic areas. The results of the polarisation measurements showed that the cobalt alloy investigated exhibits lower corrosion potential than Orthinox in the utilised environments (3% NaCl, simulated body fluid - Hank's Body Fluid). CONCLUSIONS: However, the high passivation ability of the Co-Cr-Mo alloy, as well as its resistance to the initiation and propagation of localised corrosion processes, indicate that this material is significantly more appropriate for long-term implants.