1,720,972 research outputs found
Effect of the plating parameters on the electrodeposition of Ni matrix coatings containing Ti nanoparticles
No full textElectronic properties and surface potential evaluations at the protein nano-biofilm/oxide interface: Impact on corrosion and biodegradation
Full text linkThe formation of a protein nano-biofilm, which exhibits a special electronic behavior, on the surface of metals or oxide biomaterials considerably influences the crucial subsequent interactions, particularly the corrosion and biodegradation processes. This study discusses the impact of electrical surface potential (ESP) of a single or nano-biofilm of albumin protein on the electrochemical interactions and electronic property evolutions (e.g., charge carriers, space charge capacitance (SCC), and band bending) occurring on the surface oxide of CoCrMo implants. Scanning Kelvin probe force microscopy (SKPFM) results indicated that ESP or surface charge distribution on a single or nano-biofilm of the albumin protein is lower than that of a CoCrMo complex oxide layer, which hinders the charge transfer at the protein/electrolyte interface. Using a complementary approach, which involved performing Mott-Schottky analysis at the electrolyte/protein/oxide interface, it was revealed that the albumin protein significantly increases the SCC magnitude and number of n-type charge carrier owing to increased band bending at the SCC/protein interface; this facilitated the acceleration of metal ion release and metal-protein complex formation. The nanoscale SKPFM and electrochemical analyses performed in this study provide a better understanding of the role of protein molecules in corrosion/biodegradation of metallic biomaterials at the protein nano-biofilm/oxide interface
Al2O3and HfO2Atomic Layers Deposited in Single and Multilayer Configurations on Titanium and on Stainless Steel for Biomedical Applications
No full textThin films of alumina and hafnia were prepared by atomic layer deposition, with the aim of investigating the use of such films in biomedical applications. Films were deposited on commercially pure titanium and on medical stainless steel. Two configurations were prepared: single alumina films, 20 nm and 60 nm thick, and a multilayer film, 60 nm thick, consisting of alumina/hafnia/alumina layers, each 20 nm thick. The morphology, structure and composition of the coated alloys were characterized using scanning electron microscopy with energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. In addition, ellipsometry and atomic force microscopy coupled with scanning Kelvin probe force microscopy, were used to study the thickness and the topography with surface potential properties. An improvised method, involving the Vickers hardness test, was applied to assess the delamination of the deposited films. Coated specimens, as well as bare substrates, were tested at 37 C in simulated body fluid, using potentiodynamic polarization and electrochemical impedance spectroscopy as techniques for assessing corrosion susceptibility. In general, single and multilayer thin films possess excellent barrier properties and are worth investigating further for biomedical applications. The degree of protection is dependent mainly on film thickness and on the type of substrate, and less on configuration
Heat treatments hardening effect on Ni–Al composite electrodeposits
No full textPure Ni galvanic coatings show good mechanical properties at room temperature but exhibit a progressive decrease by increasing the temperature due to the recrystallisation. A possible solution to hinder the recrystallisation is the co-electrodeposition of metal particles which could lead to the formation at high temperature of Ni alloy coatings with higher mechanical properties. Ni matrix composite deposits containing either micro (4 μm) or nano (130 nm) particles of Al were produced in a parallel plate geometry. The deposits were characterised regarding their microstructure both prior and after heat treatments for 3 h at 400, 600 and 800°C in order to evaluate the formation of Ni/Al phases. This work focused on the evaluation of the hardness on coatings cross-section by means of Vickers microhardness and Berkovich nano-indentation mapping. The results obtained with the two methods have been compared and correlated to the microstructural modifications in order to understand the hardening mechanisms. © 2018 Institute of Materials, Minerals and Mining Published by Taylor & Francis on behalf of the Institut
Corrosion mechanisms of magnetic microrobotic platforms in protein media
No full textThe field of biomedical small-scale swimmers has made major progress during the last two decades. While their locomotion aspects and functionalities have been demonstrated, there are key aspects that have been often overlooked such as their service live durability, which difficult their translation to the clinics. Several swimmers consist of combinations of metals and alloys that, while they excel in their functionalities, they fail in their stability due to corrosion in highly aggressive complex body fluids. Here, for the first time the corrosion mechanism of a widely employed design in magnetic microrobots, a gold-coated magnetic NiCo alloy, is assessed. A systematic approach by combining electrochemical and surface analysis techniques is reported, which shed light on the degradation mechanisms of these systems in simulated body fluids. While results demonstrate that Au coatings remarkably enhance the surface nobility and resistance to corrosion/biodegradation of NiCo in an aggressive environment containing albumin protein, Au coatings’ intrinsic defects lead to a galvanic coupling with the NiCo substrate. The coordination of protein with NiCo further accelerates corrosion causing morphological changes to the swimmers’ surface. Yet, the formation of a phosphate-based layer acts as a barrier to the metal release after long immersion periods
Study of the Corrosion Behaviour of Welded Systems for Marine Industry Applications
No full text5xxx (Al-Mg) and 6xxx (Al-Mg-Si) series alloys are most commonly used in the marine sector as they can guarantee both a good mechanical behaviour and good resistance to corrosion in the marine constructions. In fact, sea water contains high amounts of chlorides that can cause, after short exposure times, the failure of entire metal structures. Since in a boat there is the coexistence of different materials, it is inevitable that some of them must be welded together. Welds between dissimilar materials often require the use of non-traditional techniques, such as the process of Friction Stir Welding (FSW) and explosion welding. In this work, the resistance to corrosion of FSW joints (AA5083/AA6082) and trimetallic explosion welded joints (AA5083/AA1050/structural steel) combining galvanic coupling and immersion tests with microstructural characterization of corroded regions. In particular the focus of the work is on the corrosion behaviour of thermo-mechanically and nugget zones in FSW joints and on the AA1050/steel interface in the trimetallic joints obtained by explosion welding
Role of phosphate, calcium species and hydrogen peroxide on albumin protein adsorption on surface oxide of Ti6Al4V alloy
No full textProtein adsorption and its conformational arrangements on the surface of metallic biomaterials directly influence the biocompatibility and the degradation process during the implant lifetime. However, the presence of various species such as phosphates, calcium and hydrogen peroxide (H2O2) in the human body not only control the electrochemical interactions on the biomaterial surface but could also modify the protein adsorption process and its impact on the metal degradation. To this aim bovine serum albumin (BSA) protein adsorption, morphology, surface potential and its impact on the corrosion resistance of a Ti6Al4V alloy was investigated in different solutions, including a sodium chloride (NaCl), a phosphate-buffered saline (PBS) and Hank's physiological solutions. The results indicated that the alloy in PBS solution was more resistant to corrosion than that in Hanks’ or NaCl solutions. Mott–Schottky analysis demonstrated that all solutions containing BSA and H2O2 had the highest donor charge carrier. Scanning electron microscopy (SEM) and surface potential images indicated that by changing the physiological solutions from NaCl to PBS and then to Hanks’, the morphology of adsorbed BSA protein changed from a globular or unfolded shape to a large micronetwork and then to a fine micro-nanonetwork, accompanied by a gradual increase in the surface potential. Moreover, it was figured out that the BSA protein/substrate interface and the top surface of the BSA protein were susceptible to corrosion initiation owing to the different surface potentials and thus are preferable sites for the adsorption of corrosive counterions, e.g., Cl−
Development of a warning system for defects onset in organic coatings on large surfaces
No full textIn this work, a warning system for monitoring the service status of organic coatings over large areas was developed. Taking advantage of electrochemical impedance spectroscopy (EIS) measurements, an attempt was first made to verify the repeatability of measurements made on surfaces with gradually increasing size. A threshold value of normalized impedance modulus was then set to be an easily detectable warning signal for the testing and maintenance of protective organic coatings. Monitoring continued for nearly two years, validating the threshold value for long immersion times. It was verified that the introduction of a defect could be easily detected through this system. Introducing a number of disturbing factors into the measurement did not significantly affect the results. Finally, the use of a portable potentiostat was adopted. It was found that the use of a potentiostat with smaller size but lower sensitivity equally allowed discerning the state of protection of the organic coating, with the possibility of using the measurement system for monitoring coated surfaces used in the naval industry
Diffusive thermal treatments combined with PVD coatings for tribological protection of titanium alloys
No full textA wide array of treatments have been applied to improve the tribological behavior of titanium alloys, in particular coatings and diffusive nitrogen treatments. Hybrid technologies based on diffusive treatments and subsequent deposition of PVD coatings may further improve the overall tribological resistance. In this work, conventional PVD coatings of CrN or TiCN, deposited on Ti-6Al-4. V substrates, have been characterized and then combined with two thermal diffusive treatments: nitriding and carburizing. Post-treatment surface morphologies have been studied by means of Scanning Electron Microscopy and Stylus Profilometry. In-depth composition profiles have been obtained using Glow Discharge Optical Emission Spectrometry and localized Energy Dispersive X-Ray Diffraction. The micro-hardness and adhesion properties of the different treatments have been evaluated using Vickers micro-hardness tests at different load conditions and confronting the hardness vs load profiles. The tribological behavior of the different treatments has been tested in dry conditions in alternate pin-on-flat configuration. The standalone PVD coatings showed a limited tribological resistance due to the low hardness of the substrate, which resulted in fractures and delamination. The combination of a hardening process followed by a deposition of a PVD coating showed to strongly improve the tribological resistance of Ti-6Al-4. V. © 2015 Elsevier Ltd
On growth and morphology of tio2 nanotubes on ti6al4v by anodic oxidation in ethylene glycol electrolyte: Influence of microstructure and anodization parameters
Full text linkDifferent studies demonstrated the possibility to produce TiO2 nanotubes (TNTs) on Ti6Al4V alloy by electrochemical anodization. However, the anodizing behavior of α and β-phases in organic electrolytes is not yet clarified. This study reports on the anodizing behavior of the two phases in an ethylene glycol electrolyte using different applied potentials and anodizing times. Atomic force and scanning electron microscopies were used to highlight the anodic oxides differences in morphology. It was demonstrated that the initial compact oxide grew faster over the β-phase as the higher Al content of the α-phase caused its re-passivation, and the higher solubility of the V-rich oxide led to earlier pores formation over the β-phase. The trend was inverted once the pores formed over the compact oxide of the α-phase. The growth rate of the α-phase TNTs was higher than that of the β-phase ones, leading to the formation of long and well defined nanotubes with thin walls and a honeycomb tubular structure, while the ones grown over the β-phase were individual, shorter, and with thicker walls
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