ABSTRACT
Nanocomposite films of ZrN-Ag were produced by reactive unbalanced magnetron sputtering, and their structural, chemical, mechanical, tribological, haemocompatibility, and antibacterial properties were studied as a function of film composition. The films formed a dense and homogeneous microstructure whereby nanocrystals of Ag are distributed evenly throughout the ZrN matrix. For small additions of silver, the hardness was found to increase, whereas the elastic modulus was found to decrease drastically. In the process of optimizing the deposition conditions, three kinds of coatings were prepared on 316 L surgical steel and tested by accelerated electrochemical polarization tests in order to detect the influence of Ag and the value of the bias potential on the corrosion performance of the system. Films produced under the optimum deposition conditions were, subsequently, deposited on medical grade Ti-Al-V and worn against ball-bearing steel using a ball-on-disk tribotester in bovine serum and were found to have superior tribological properties compared with single-phase ZrN coatings. The haemocompatibility of the films was assessed by investigating the adsorption of human serum albumin and fibrinogen on samples with different phase compositions. Quantification of the protein adsorption was carried out using spectroscopic ellipsometry, which confirmed the haemocompatibility of the films. Antibiotic activity of the films was quantified by incubating the films in bacterial cultures, namely, Staphylococcus epidermis, Staphylococcus aureus, and Escherichia coli. Films with a silver content > 10% exhibited superior antibacterial activity compared with the uncoated samples.
Subject(s)
Biocompatible Materials/chemistry , Nanocomposites/chemistry , Nitrogen/chemistry , Silver/chemistry , Zirconium/chemistry , Adsorption , Anti-Infective Agents/chemistry , Electrochemistry/methods , Escherichia coli/metabolism , Humans , Materials Testing , Serum Albumin/chemistry , Silver/pharmacology , Staphylococcus aureus/metabolism , Staphylococcus epidermidis/metabolism , Surface PropertiesABSTRACT
This study was performed with the aim of evaluating the relative tribological behaviour at high temperature of (Ti(1-x)Al(x))N coatings commercially deposited on WC inserts. The (Ti(1-x)Al(x))N multilayered, nanostructured and single-layer coatings, which contained different Ti/Al atomic ratios varying from 7/3 to 2/3 respectively, were deposited by employing a commercial PVD cathodic arc process. The absolute hardness value for each coating is also reported and has been calculated from the Vickers microhardness measurements by using one of the models published in the literature. Standard ball-on-disc testing was conducted in order to determine friction coefficients and wear rates for these systems against a 6 mm alumina ball. These tests have been carried out in conditions that are not common in industrial use, e.g. metal cutting tools inasmuch as alumina is not a representative workpiece material. The sliding tests were performed out at 25, 500 and 700 °C with 5 N normal loads. At 25 °C, a wear volume, V, of approximately 10(-2) mm(3) was obtained for all the tested coatings. When the test temperature increased to 500 °C, the single-layered coatings showed a wear volume of the same order of magnitude as those tested at room temperature. The multilayered coated samples decreased their wear volume by one order of magnitude, whereas the nanostructured samples showed almost no wear. At 700 °C, the wear volume values reported for all samples were similar and of the same order of magnitude as those tested at room temperature. The wear mechanism is discussed together with the morphological and compositional characteristics, determined by SEM coupled with EDX analysis.
