Publicação
Production and characterization of ZrCN-Ag coatings deposited by mganetron sputtering
| Resumo: | Zr-C-N coatings, incorporating silver as antibacterial agent, are deposited onto stainless steel 316L (SS316L) and Si (100) substrates by unbalanced magnetron sputtering; their corrosion and tribological properties were evaluated to understand their potential to be used in joint orthopedic devices. Zirconium carbonitride was selected owing to both its excellent biocompatibility and non-toxic behavior. Despite ZrCN has been widely studied, no other report on the deposition and characterization of Zr-C-N-Ag coatings exist in the literature, to the author knowledge. Therefore, the contribution of this project for the state of the art on Zr-C-N system alloyed novel metallic elements is: (i) A structural characterization, including the phase composition, based on the identification of crystalline (X-ray diffraction and transmission electron microscopy) and amorphous phases (Raman spectroscopy), and the chemical composition of the material both in bulk (electron probe microanalysis) and at the surface (X-ray photonelectron spectroscopy). The morphology of the coatings was also studied (scanning electron microscopy), in order to evidence the influence of the deposition parameters on the coatings cross-section and surface morphology, and correlate them with the functional properties. (ii) In order to optimize the adhesion, mechanical and electrochemical properties of the coatings; an optimization method was applied to the deposition process to decrease the final number of coating runs. (iii) The in-depth electrochemical and tribological characterization of the coatings was performed in a Hank’s balanced salt solution with 10 gr/L of bovine serum albumin, in order to mimic as much as possible the condition of the biological fluid of human body. In Zr-C-N-Ag system a diversity of phases can occur, such as zirconium carbonitride (ZrCN), amorphous carbon (a-C or a-(C, N)) and metallic silver (Ag). By controlling the deposition conditions, it is possible to adjust the amount of each phase, and then, to tune the properties of the system. The optimization of the deposition process shows that the ideal composition of the Zr-C-N-Ag coatings is attained when the Zr2CN phase is deposited, with less than 8 at. % of silver nanoparticles, allowing achieving the best compromise between mechanical, electrochemical and tribological properties. The electrochemical evaluation reveals that both silver and amorphous carbon phases are detrimental to the corrosion resistance. The increase of silver triggers a more active electrochemical reactions in the system that increases the corrosion process. In addition, the combination of silver and amorphous phases produces a more electrochemical porous materials, which promotes the penetration of the electrolyte. Although marginally, silver also negatively affects the wear resistance of the system, when tested against an ultra-high molecular weight polyethylene, due to a delay it causes in the formation of a protective albumin layer. The coefficient of friction (COF) of the coatings, did not show any correlation with the amount of silver, while the amorphous carbon phases seems to reduce the COF. Finally, the phase distribution showed a relevant role in the silver ion release to the electrolyte, as a function of the silver nanoparticles surrounding. This distribution of phases creates nanogalvanic couples in the system that controls the silver ion release, depending on a:C or ZrCN phases, the oxidation of silver can be enhanced or retarded, respectively. The antibacterial effect of the system does not have a direct relation with the silver ion release. Even coatings with low silver ion release may possess antibacterial capabilities, if silver is highly agglomerated on the surface. |
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| Autores principais: | Velasco, Sebastian Calderon |
| Assunto: | Engenharia e Tecnologia::Engenharia dos Materiais |
| Ano: | 2016 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade do Minho |
| Idioma: | português |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | Zr-C-N coatings, incorporating silver as antibacterial agent, are deposited onto stainless steel 316L (SS316L) and Si (100) substrates by unbalanced magnetron sputtering; their corrosion and tribological properties were evaluated to understand their potential to be used in joint orthopedic devices. Zirconium carbonitride was selected owing to both its excellent biocompatibility and non-toxic behavior. Despite ZrCN has been widely studied, no other report on the deposition and characterization of Zr-C-N-Ag coatings exist in the literature, to the author knowledge. Therefore, the contribution of this project for the state of the art on Zr-C-N system alloyed novel metallic elements is: (i) A structural characterization, including the phase composition, based on the identification of crystalline (X-ray diffraction and transmission electron microscopy) and amorphous phases (Raman spectroscopy), and the chemical composition of the material both in bulk (electron probe microanalysis) and at the surface (X-ray photonelectron spectroscopy). The morphology of the coatings was also studied (scanning electron microscopy), in order to evidence the influence of the deposition parameters on the coatings cross-section and surface morphology, and correlate them with the functional properties. (ii) In order to optimize the adhesion, mechanical and electrochemical properties of the coatings; an optimization method was applied to the deposition process to decrease the final number of coating runs. (iii) The in-depth electrochemical and tribological characterization of the coatings was performed in a Hank’s balanced salt solution with 10 gr/L of bovine serum albumin, in order to mimic as much as possible the condition of the biological fluid of human body. In Zr-C-N-Ag system a diversity of phases can occur, such as zirconium carbonitride (ZrCN), amorphous carbon (a-C or a-(C, N)) and metallic silver (Ag). By controlling the deposition conditions, it is possible to adjust the amount of each phase, and then, to tune the properties of the system. The optimization of the deposition process shows that the ideal composition of the Zr-C-N-Ag coatings is attained when the Zr2CN phase is deposited, with less than 8 at. % of silver nanoparticles, allowing achieving the best compromise between mechanical, electrochemical and tribological properties. The electrochemical evaluation reveals that both silver and amorphous carbon phases are detrimental to the corrosion resistance. The increase of silver triggers a more active electrochemical reactions in the system that increases the corrosion process. In addition, the combination of silver and amorphous phases produces a more electrochemical porous materials, which promotes the penetration of the electrolyte. Although marginally, silver also negatively affects the wear resistance of the system, when tested against an ultra-high molecular weight polyethylene, due to a delay it causes in the formation of a protective albumin layer. The coefficient of friction (COF) of the coatings, did not show any correlation with the amount of silver, while the amorphous carbon phases seems to reduce the COF. Finally, the phase distribution showed a relevant role in the silver ion release to the electrolyte, as a function of the silver nanoparticles surrounding. This distribution of phases creates nanogalvanic couples in the system that controls the silver ion release, depending on a:C or ZrCN phases, the oxidation of silver can be enhanced or retarded, respectively. The antibacterial effect of the system does not have a direct relation with the silver ion release. Even coatings with low silver ion release may possess antibacterial capabilities, if silver is highly agglomerated on the surface. |
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