Electroplating processes are widely used on several aeronautical applications to confer functional properties (electrical conductivity, tribological, anti-corrosion). In this industrial context, it is possible to keep the desired properties by respecting specifications such as thicknesses and coating composition for alloys. However, it is well-known that phenomena intrinsic to electrochemical processes create heterogeneities, especially on complex geometries like landing gears. Industrially, the treatment of these disparities is part of the know-how of the workshops, and they are balanced by complex auxiliary tools in order to obtain a more uniform local current densities distribution, and therefore coating thickness. The development of these specific anode shapes is time-consuming and depends strongly of an empirical know-how. The numerical simulation of electrochemical processes is developed at Safran Tech in collaboration with Institute Utinam to optimize the development of plating tools at industrial scale with ComsolÒ Multiphysic software. The global objective is to improve the reliability of the existing systems, and moreover to enhance the innovation by facilitating new coatings integration. This is crucial in the context of tightening of environmental REACH regulations, such as the substitution of cadmium by zinc-nickel. Modeling industrial electroplating processes by a secondary current distribution model is evaluated in terms of thickness prediction by a comparison with experimental results at a laboratory scale pilot. It has been emphasized that the main limitation are due to the failure to take full account of mass transport induced by convection. The study also participate to the development of good practice for auxiliary tools design, and the simulation demonstrate invaluable assistance in industrial operations. Figure 1
Electrochemical polishing (EP) is of great interest because it is able to deal with small parts exhibiting high complex shapes and/or material hard to be polished. Electropolishing is an electrolytic process based on the anodic dissolution of the workpiece under constant current or potential. Previous work done on stainless steel 316L shows the ability of the process to obtain smooth and bright surfaces [1]. The mechanisms describing EP are not yet fully understood, but several mechanisms can be taken into account for its description and prediction. Jacquet’s theory is based on the influence of an electric resistance gradient [2]. Elmore will then complete it with the gradient of concentration in metal cation [3,4]. Diard and al proposed the role of so called “acceptor” species [5]. While Hoar and Mowat’s work are based on the formation of an oxide layer on the surface [6]. All theories have in common the establishment of a viscous layer (solid or liquid) that governs the process. On this basis, it is possible to propose a numerical approach for the simulation of the viscous layer formation during electropolishing of stainless steel 316L and Inconel parts. The objective is to demonstrate the impact of various process parameters (electrochemical parameters, electrolyte nature and concentration as well as hydrodynamic conditions) on the growth and the stability of this layer. The figure illustrate the simulation of the viscous layer growth during the electropolishing of a plate at the bottom taking into account the circulation of the electrolyte from the left to the right. [1] C. Rotty, A. Mandroyan, M-L Doche, J-Y Hihn, Surface & Coatings Technology vol.307 p125–135 (2016). [2] JACQUET, P.A., Electrolytic method for obtaining bright copper surfaces, Nature 135 (1935) 1076. [3] ELMORE, W.C., Electrolytic Polishing, J. Appl. Phys. 10 (1939) 724–727, http://dx.doi.org/10.1063/1.1707257. [4] ELMORE, W.C., Electrolytic Polishing II, J. Appl. Phys. 11 (1940) 797–799, http://dx.doi.org/10.1063/1.1712738. [5] DIARD, J.P., LANDAUD, P., LE CANUT, J.-M., LE GORREC, B., Interprétation cinétique du palier de polissage électrochimique des métaux, 6ème forum sur les impédances électrochimiques, Montrouge, 1992. [6] HOAR, T.P., MOWAT, J.A.S., Mechanism of electropolishing, Nature 165 (1950) 64–65. Figure 1
Copper is the most widely used materials for microelectronics applications due to their electrical and thermal conduction properties, and in several appplications, thick and porous layers are requested. Different possibilities still exists such as copper-zinc or copper-manganese electrodeposition followed by an anodic dissolution, but the faster and simpler way resides in electroforming deposition made by Dynamic Hydrogen Bubble Template (DHBT) [1]. This process works in unusual potentials and current densities where the competition between hydrogen discharge (commonly avoided) and copper reduction is very high. In this case, this method achieves thick deposits in very short time (few seconds) with high currents allowing a very fast growth of copper around hydrogen bubbles. Pores and ligaments sizes can be controlled by several operating parameters i.e. current densities, temperature, deposit time as well as by chemical additives [2]. With the use of a copper sulphate acid bath at various concentrations, with or without additives (acetic or hydrochloric acids) and by applying current densities between 100 and 400 A.dm-2, it is possible to obtain thick and porous coatings, with pores diameters between 10 and 500 µm and ligaments length between 10 and 200 µm. An example of a SEM image shows the morphology of the deposits obtained in top view and in cross section (Figure 1). Another possibility to control the 3D growth resides in the use of pulsed currents, with an effect on bubbles size. Furthermore, reverse pulses are useful for edge effects limitation. [1] Abdel-Karim, R.; El-Raghy, S. Chap 4 in Advanced materials and their applications - micro to nano scale. One Central Press, United Kingdom, pp 69–91, 2017 [2] Shin, H.-C.; Liu, M. Chem. Mater. 2004, 16, 25, 5460–5464 doi.org/10.1021/cm048887b Figure 1 : SEM images of a) top view and b) cross section of a DHBT copper deposit Figure 1
Nowadays, 40% of the world wide used energy is provided by electric power and this share should reach about 60% by 2040. For environmental reasons, it is crucial to ensure low dissipation loss in power electronic devices by optimizing energy conversion. In the field of renewable energies and automotive electronics, possible energy savings are estimated to be between 20 and 35%. For that purpose, innovative power components and modules are required, with a growing interest for fast and simple joining processes in their fabrication management, in the case for example of the assembly of large-size double-side cooled modules. Several options are possible, including free sintering of metallic pastes or electroforming welding. In all cases, this requires a great control of both surfaces to be joined, mostly prepared by electrodeposition (microstructure, porosity, alloy composition). But the final properties of electrodeposited coatings are strongly dependent of the first nucleation steps, which influence the whole layer structure. In this frame, the modelling of a nucleation process followed by diffusion limited three dimensional growth is an area of promising interest. The study of potentiostatic current transients is a relevant methodology, allowing the determination of several parameters such as nucleation rate, nucleus density, and number of active sites. Different competing models are available, such as Scharifker and Hills [1] and Scharifker and Mostany [2]. By using the model method i.e. the identification of the model parameters by error minimization, it is possible to reach an accurate description of the first layer growth in the case of different metals such as silver and copper. Nevertheless, little attention have been paid to changes in hydrodynamic conditions, for example in the study of current response under forced convection [3]. The present work describes the extension of the model method to the modelling of the first steps of nucleation growth in the case of a sample exposed to an ultrasonic irradiation, which was compared to forced convection induced by a rotating disc electrode at the very same agitation level (equivalent velocity [4,5]. Eventually, the case of electrodeposited alloys was examined, as a function of their Brenner classifications (anomalous and normal codeposition [6]). The limitation of the data processing by the numerical approach are also discussed. [1] Scharifker, B. & Hills, G. Theoretical and experimental studies of multiple nucleation. Electrochimica Acta 28, 879–889 (1983). [2] Scharifker, B. R. & Mostany, J. Three-dimensional nucleation with diffusion controlled growth. J. Electroanal. Chem. Interfacial Electrochem. 177, 13–23 (1984). [3] Hyde, M. E. & Compton, R. G. Theoretical and experimental aspects of electrodeposition under hydrodynamic conditions. J. Electroanal. Chem. 581, 224–230 (2005). [4] Pollet B.G., Hihn J.-Y., Doche M.L, Mandroyan A., Lorimer J.P., Mason T.J “Transport limited currents close to an ultrasonic horn: equivalent flow velocity determination”, Journal of Electrochemistry Society, 154(10), E131-E138, (2007) [5] A. Nevers, L. Hallez, F. Touyeras, J.-Y. Hihn, Effect of ultrasound on silver electrodeposition: Crystalline structure modification, Ultrason. Sonochem. 40 (2018) [6] Brenner, A. Electrodeposition of alloys. Principles and practice Volume II, (1963).
Long-term protection of metallic parts from atmospheric exposure is an important challenge and one of the most frequent way to ensure their corrosion resistance is the application of sacrificial zinc alloys coatings [1]. Among the various zinc electroplating baths, the alkaline zincate solutions has gained a wide range of applications thanks to its simple bath composition, good dispersion and efficient coverage ability. Nevertheless, its efficiency is very low in absence of additives, which affects the performances of the coatings by modifying the crystal growth and therefore the structural and mechanical properties. This is a result from the competition between dihydrogen production and the reduction of the metallic species present in the bath.The present study deals with the optimization of ZnFe sacrificial coating on steel and aluminum substrate in the frame of the ATLAS project -Alternative TechnoLogies for improved Anticorrosion Solutions- managed by the IRT M2P. After the analysis of the electrochemical behavior of the ZnFe electrolyte patented by the Coventya company and the UTINAM institute, pulsed currents will be implemented to extend the versatility of the coatings. Indeed, pulsed currents are known to act on various parameters such as improving the faradic yield or modifying morphologies and structures [2].The determination of a first panel of pulsed sequences (average current densities, cathodic peak current, cathodic pulse time and off-time) have been based on transient curves analysis from a zincate bath. Three sequences have been selected as they resulted in very different patterns in terms of electrochemical behavior and coatings characteristics. These sequences have been replicated and compared to DC current in several electrolytes, from the zincate bath to the commercial formula. For each set of parameters, the faradic yield has been measured and compared to the hydrogen generated during the electrolysis distributed between the absorbed one (measured by hot extraction) and the dihydrogen released into the reactor atmosphere (measured by mass spectrometry with a dedicated set- up). It is interesting to note that the obtained values strongly depend on pulsed sequences as well as electrolytes composition. Coatings were systematically produced and characterized. Morphology was observed using SEM and microstructure determined from XRD diffractograms: preferential orientation and crystal lattice and crystalline phases. The latest has required a specific methodological development.Finally, the identification of nucleation parameters by model simulation has been undertaken to describe the mechanisms involved in the first steps of zinc electrodeposition [3].[1] B. Chatterjee, « Electrodeposition of Zinc Alloys », p. 31.[2] X. Zhang, K. Tsay, J. Fahlman, and W. Qu, « Journal of Energy Storage, 26 p. 100966 (2019)[3] A. Milche, Electrochimica Acta, 48 p.2903-2913 (2003)
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