Statistical Study of the Corrosion Behavior of Al2CuMg Intermetallics in AA2024-T351 by SKPFM

A statistical study combining atomic force microscopy, scanning Kelvin probe force microscopy (SKPFM), and energy-dispersive spectroscopy was carried out on more than 300 Al2CuMg intermetallic particles of AA2024 alloy to determine their corrosion behavior in chloride-containing solutions. The combination of these three techniques allowed the correlation of the dissolution depth of the S-phase particles to their SKPFM potential and their chemical composition. This study also revealed that SKPFM measurements must be carried out with many precautions, but it is a powerful tool for the study of localized corrosion

Combination of AFM, SKPFM, and SIMS to Study the Corrosion Behavior of S-phase particles in AA2024-T351

The dissolution mechanism of S-phase particles in 2024-T351 aluminum alloy at open-circuit potential in chloride-containing sulfate solutions was investigated using atomic force microscopy (AFM), scanning Kelvin probe force microscopy (SKPFM), and secondary ion mass spectroscopy (SIMS). The combination of the three techniques allowed the correlation between SKPFM measurements and the corrosion behavior of AA2024 to be confirmed, leading to a better understanding of the electrochemical behavior of S-phase particles. A three-step mechanism for the dissolution and accompanying processes occurring near S particles was proposed: (i) preferential aluminum and magnesium dissolution, (ii) galvanic coupling between the copper-enriched particles and the surrounding matrix, leading to an increased passivity of the matrix around the particles, and (iii) copper deposition around the corroded particles

Localized approach to galvanic coupling in an aluminum–magnesium system

The corrosion behavior of a pure aluminum/pure magnesium couple in a weakly conductive sodium sulfate solution was investigated. Potential and current distributions on the surface of the model couple at the beginning of immersion were obtained by solving the Laplace equation using a finite element method algorithm. Magnesium acted as the anode of the system while oxygen and water were reduced on aluminum. Calculations predicted a large current peak at the Al/Mg interface related to a local increase in both Mg dissolution and oxygen and water reduction on aluminum, leading to a local pH increase. Optical and scanning electron microscope observations confirmed the strong dissolution of magnesium concomitantly with depassivation of aluminum at the Al/Mg interface. Local electrochemical impedance spectroscopy showed the detrimental effects of the galvanic coupling both on aluminum and magnesium

Simulating the galvanic coupling between S-Al2CuMg phase particles and the matrix of 2024 aerospace aluminium alloy

Study of the corrosion behaviour of a magnetron sputtered Al–Cu/Al–Cu–Mg model alloy couple in sulphate solutions has been undertaken to gain insight into the galvanic coupling between the matrix and SAl2CuMg particles in the 2024 aluminium alloy (AA2024). Polarisation curves and local electrochemical impedance spectroscopy measurements (LEIS) were performed on the individual alloys and on the model alloy couple. SEM enabled correlation of electrochemical phenomena to the observed damage. The corrosion behaviour of the sputtered alloys was shown to be representative of the AA2024, with the Al–Cu–Mg alloy part undergoing localised corrosion and the Al–Cu alloy part remaining passive

Combined Kelvin probe force microscopy and secondary ion mass spectrometry for hydrogen detection in corroded 2024 aluminium alloy

The capability of Kelvin probe force microscopy (KFM) to detect and locate hydrogen in corroded 2024 aluminium alloy was demonstrated. Hydrogen was introduced inside the 2024 alloy following a cyclic corrosion test consisting of cycles of immersion in 1 M NaCl solution followed by exposure to air at -20 °C. The combination of scanning electron microscopy, secondary ion mass spectrometry and KFM demonstrated that the grain and subgrain boundaries were preferential pathways for the short-circuit diffusion of hydrogen but also acted as a source of hydrogen diffusion in the lattice over distances of up to ten microns with non-negligible desorption when exposed to air at room temperature for 24 h

Investigation of Kelvin probe force microscopy efficiency for the detection of hydrogen ingress by cathodic charging in an aluminium alloy

Detecting and locating absorbed hydrogen in aluminium alloys is necessary for evaluating the contribution of hydrogen embrittlement to the degradation of the mechanical properties for corroded or cathodically hydrogen-charged samples. The capability of Kelvin probe force microscopy (KFM) to overcome this issue was demonstrated. Aluminium alloy samples were hydrogenated by cathodic polarisation in molten salts (KHSO4/NaHSO4.H2O). The presence of absorbed hydrogen was revealed; the affected zone depth was measured by secondary ion mass spectroscopy (SIMS) analyses and KFM measurements

Hydrogen diffusion and trapping in a low copper 7xxx aluminium alloy investigated by Scanning Kelvin Probe Force Microscopy

The susceptibility to hydrogen embrittlement (HE) of the 7046 aluminium alloy (AA 7046) was investigated. Samples of AA 7046 corresponding to different ageing temperature/time couples were hydrogenated by cathodic charging in a H2SO4 solution. Scanning Kelvin Probe Force Microscopy (SKPFM) combined with global hydrogen amount measurements allowed apparent hydrogen diffusion coefficients (Dapp) to be measured: the decrease of the Dapp values with the increase of the ageing duration was attributed to hydrogen trapping by hardening η’ and η precipitates for the aged alloy. Additional SKPFM measurements were carried out on hydrogen charged samples after desorption at 25 °C and combined with SEM observations of the fracture surfaces after tensile tests. Results showed that hydrogen could be trapped at the grain boundaries leading to brittle intergranular fracture. However, hardening precipitates could act as efficient trapping sites and reduce hydrogen trapping at the grain boundaries. Conclusion is that the most critical microstructural parameters for HE of AA 7046 correspond to the grain boundaries while ageing could contribute to improve the resistance to HE of the alloy by a well-controlled precipitation

Granular Jamming as Controllable Stiffness Mechanism for Endoscopic and Catheter Applications

Context During minimally invasive procedures, most of the devices (endoscopes, catheters, guidewires, etc.) need to be sufficiently flexible to avoid damaging patient tissues or causing pain, but have to be stiff enough to transmit force for support or for puncture. In the case of vascular stenosis, the guidewire has to be flexible to reach the stenosis (through the blood vessels), but it requires a rigid support to pass through the occlusion for treatment, to avoid buckling or deformation due to the force application. In order to solve this duality on the rigidity, controllable stiffness mechanisms can be used. Various mechanisms to control the stiffness can be found in the literature [1]. One of the promising solutions to achieve this objective is based on granular material jamming [2]. This research aims at studying the scaling laws of such solutions for miniaturized applications (with diameters below 3mm), the mechanical rules of design and the optimization based on the stiffness performances. Granular jamming The granular jamming is based on the locking of granular material. In this study, a flexible membrane is filled with a granular material (glass beads). When the pressure difference between outside and inside the membrane is low, the grains are free to move with respect to each other. In this configuration, the system is very flexible. Once the difference of pressure is increased, the grains are locked to each other due to the inter-grain friction. In this configuration, the system is more rigid. It is possible to adjust the stiffness of the device by controlling the pressure difference across the membrane. Materials and methods In this work, the performances of the stiffness change thanks to the granular jamming are quantified by mechanical testing. On the one hand, three point bending and cantilever beam tests are performed to quantify the flexural stiffness EI (product of the Young Modulus, E, and the second moment of area, I) of the solutions. Various granular materials and diameters of the samples are studied. On the other hand, triaxial compression tests are performed to observe the influence of the pressure difference on the rigidity obtained via granular jamming, using different granular materials. Results and discussion The tests described previously provide information on the performances of the granular jamming solution as well as an indication of the most important parameters to optimize. An optimal size of grains is highlighted by the results of these mechanical tests. The results of the triaxial compression tests show that the pressure difference is the most important parameter influencing the Young Modulus. The bending tests show that the second moment of area greatly impacts this stiffness. Removing the influence of the geometry, the equivalent Young Modulus is positively influenced for smaller diameters which is promising for the applications targeted in this work. Some of these results, as well as pictures and conclusions are illustrated in the poster file available in the following link : https://dipot.ulb.ac.be/dspace/bitstream/2013/239703/3/20161125PosterNCBMElblanc.pdf. One of the perspectives of this work is to develop a model for linking the results obtained from the different mechanical tests and to observe the optimization of the grains (shape and size) and cross-section of the samples with respect to the change of stiffness obtained. Further studies on stimulation method and on materials should be performed. References - [1] Kuder, I. K. et Al., ?Variable stiffness material and structural concepts for morphing applications?, Progress in Aerospace Sciences, pp.33-55, 2013. - [2] Loeve, A. J. et Al., ?Vacuum packed particles as flexible endoscope guides with controllable rigidity?, Granular Matter, pp. 543-554, 2010

A Kelvin probe force microscopy study of hydrogen insertion and desorption into 2024 aluminum alloy

Hydrogen was inserted into 2024 aluminum alloy by cathodic polarization in sulfuric acid at 25 °C. Scanning Kelvin Probe Force Microscopy (SKPFM) measurements performed perpendicularly to the charging side revealed a potential gradient and confirmed the insertion of hydrogen over hundreds of microns. A hydrogen diffusion coefficient of 1.7 x 10-9 cm2 s-1 was calculated from SKPFM measurements of H-charged samples for different durations. The evolution of the potential gradient during desorption of hydrogen in air, at room temperature and at 130 °C was investigated. Additional experiments performed at a corrosion defect showed that SKPFM could detect both reversibly and irreversibly bounded hydrogen. These results show that SKPFM is a cutting-edge technique for hydrogen detection and localization at a local scal

Proteus, des web services pour les systèmes de maintenance

Colloque avec actes et comité de lecture. nationale.National audienceLe projet PROTEUS a comme objectif de fournir une plate-forme et les concepts génériques pour construire des systèmes de e-maintenance industrielle incluant les systèmes existants d'acquisition de données, de contrôle - commande, de gestion de la maintenance, d'aide au diagnostic, de gestion de la documentation, etc. Le but de la plate-forme est non seulement d'intégrer des outils existants, mais aussi de prévoir l'évolution de celle-ci au travers de l'introduction de nouveaux services. Les concepts de Web services, d'ontologie et de services génériques associés à des modèles génériques des données sont au centre de la solution en cours de développement. En effet, ces techniques permettent de garantir l'interopérabilité de systèmes hétérogènes. Cet article décrit les principes de la solution en s'appuyant sur un exemple de processus et un scénario typique de maintenance corrective. De plus, il décrit les résultats préliminaires obtenus lors des premières expérimentations