Liste des publications
Effect of Immersion Time and Cooling Mode on the Electrochemical Behavior of Hot-Dip Galvanized Steel in Sulfuric Acid Medium
In this work, we investigated the influence of galvanizing immersion time and cooling modes environments on the electrochemical corrosion behavior of hot-dip galvanized steel, in 1 M sulfuric acid electrolyte at room temperature using potentiodynamic polarization technique. In addition, the evolution of thickness, structure and microstructure of zinc coatings for different immersion times and two cooling modes (air and water) is characterized, respectively, by using of Elcometer scan probe, x-ray diffraction and metallography analysis. The analysis of the behavior of steel and galvanized steel, vis-a-vis corrosion, by means of corrosion characteristic parameters as anodic (βa) and cathodic (βc) Tafel slopes, corrosion potential (Ecorr), corrosion current density (icorr), corrosion rate (CR) and polarization resistance (Rp), reveals that the galvanized steel has anticorrosion properties much better than that of steel. More the immersion time increases, more the zinc coatings thickness increases, and more these properties become better. The comparison between the two cooling modes shows that the coatings of zinc produced by hot-dip galvanization and air-cooled provides a much better protection to steel against corrosion than those cooled by quenching in water which exhibit a brittle corrosive behavior due to the presence of cracks. Voir les détails
Mots clés : cooling mode, hot-dip galvanization, Metallography, Potentiodynamic polarization, steel, X-ray diffraction, zinc coating
Microstructure and microindentation of Ti3SiC2–Titaniumfiller brazedjoints by tungsten inert gas (TIG) process.
Herein we study the joining of Ti3SiC2- a MAX phase - with a Tifiller (Ti3SiC2/Ti-filler) using a TIG-brazingprocess. The microstructures of the interfaces were investigated by scanning electron microscopy and energydispersive spectrometry. When Ti3SiC2comes into contact with the molten Ti -filler during the TIG-brazingoperation, it starts decomposing into TiCxand a Si-rich liquid. Simultaneously, the molten Ti infiltrates into theTi3SiC2resulting in a 200 µm thick duplex region, comprised of TiCxand a Ti-rich phase with some dissolved Si.Both Si and C are found in the solidified Ti; the Si source is from the Si-rich liquid, while the presence of Cindicates that some of the C diffused into the Ti. Upon cooling, C- containing Ti- rich lamellae form the solidifiedTi. Microindentation results of the decomposed Ti3SiC2layer show an increase in hardness and a decrease inelastic modulus relative to T3SiC2. Notably, no cracks were observed Voir les détails
Mots clés : MAX Phases, Microstructures, Joining, hardness, Micro-indentation
Microstructure and Magnetic Properties of NiP Alloys
Ni-P alloys were prepared by electrodeposition on a copper substrate at different plating conditions (applied potential and deposition time). The morphology, composition, microstructure, structure, and magnetic properties of the films were investigated by scanning electron microscopy, energy-dispersive spectrometry, X-ray diffraction, and vibrating sample magnetometry, respectively. The phosphorous content is about 8.6–12.2 at.%. The deposits exhibit either a nanocomposite structure where Ni(P)–1 and Ni(P)–2 solid solutions are embedded into an amorphous matrix, or a mixture of Ni2P phosphide and Ni(P)–1 and Ni(P)–2 solid solutions. The coercivity and magnetization are plating condition dependent. All samples exhibit a soft magnetic character with coercivity lower than 58 Oe. The squareness ratio Mr/Ms values that are in the range 0.019–0.123 correspond to a multidomain (<0.1) for all samples except sample B (−1.15 V, 10 min) which falls into a pseudo-single domain (Mr/Ms = 0.123). Voir les détails
Mots clés : Electrodeposition Ni-P alloys Microstructure Magnetic properties X-ray diffraction
Physical investigations on perovskite LaMnO3-δ sprayed thin films for spintronic applications
Oxygen deficient LaMnO3 thin films were successfully grown on glass substrate by spray pyrolysis at 460 °C. XRD studies show oxygen vacancies corresponding to the orthorhombic La4Mn4O11 with (040) preferential orientation. Optical properties were investigated through optical band gap and Urbach energy. The dispersion of the refractive index was discussed in terms of both Cauchy and Wemple & Di-domenico models. Raman spectroscopy shows the band positions corresponding to LaMnO3 with a shift related to oxygen deficiency. Electrical properties were quantified using impedance spectroscopy technique within frequency range of 5 Hz–13 MHz at various temperatures. Both the DC conductivity and relaxation frequency were thermally activated with activation energy around 0.9 eV. Also, AC conductivity was investigated through Jonscher law. Finally, magnetic measurements at room temperature using vibrating sample magnetometer (VSM) technique show ferromagnetic behavior of these ternary sprayed thin films. Voir les détails
Mots clés : Thin films, Magnetic Properties, Raman spectroscopy, Impedance spectroscopy, X-ray diffraction, Dielectric properties
EFFET DE LAMINAGE A CHAUD SURLE COMPORTEMENT DE LARECRYSTALLISATION DE L’ACIERINOXYDABLE FERRITIQUE TYPE 409
The behavior of the static recrystallization of this ferritic stainless steel type 409 which contains precipitateswas examined using hot rolling test of a single pass. Hot rolling tests were carried out at temperature of 870°C from athickness of 15mm to 8,4mm and 4,7mm thickness at a controled strain rate of 3.3s-1. The recrystallized volumeincreases with the increase of the reduction and the holding time after hot rolling. Nucleation of recrystallising grainsappears to be associated with triple points and grain boundaries. This material displays a slower rate of recrystallisationand this is attributed to the presence of titanium Voir les détails
Mots clés : ferritic stainless steel type 409, precipitates, deformation variables, hot rolling, dynamic recovery, static recovery, static recrystallization
Nonlinear predictive control of a mobile robot: asolution using metaheuristcs
The basic features of model-based predictive control (MBPC) make it an interesting candidate for the control of mobile robots. However, fast solution procedures remain a challenge for nonlinear MBPC problems such as the one arising in mobile robot control. Metaheuristics are general purpose heuristics which have been successful in solving difficult optimization problems in a reasonable computation time. In this work, we present a comparison between the uses of three different heuristics, namely particle swarm optimization (PSO), ant colony optimization, and gravitational search algorithm for the solution of the nonlinear MBPC for a mobile robot tracking trajectory with dynamic obstacle avoidance. The computation times obtained show that PSO is a feasible alternative for real-time applications. The MBPC based on the PSO is applied to controlling a LEGO mobile robot with encouraged results. Voir les détails
Mots clés : nonlinear predictive control, Metaheuristcis, mobile robots, optimization
Beta to alpha transformation kinetics and microstructure of Ti-6Al-4Valloy during continuous cooling
In the present paper, an approach based on the Kolmogorov-Johnson-Mehl-Avrami (KJMA) model hasbeen developed and applied to study the transformation kinetics of the b phase in Ti-6Al-4V titaniumalloy during cooling. To this purpose, Differential Scanning Calorimetry (DSC) tests have been conductedusing a set of cooling rates ranging from 10 to 50 C/min. This approach allows the kinetics parameters,particularly the activation energy, to be calculated from a single DSC test using a simple linear regression.The microstructural analysis indicates that the microstructure is dominated by the a Widmanstatten €morphology (aW). Microstructural observations along with the calculated values of the Avrami index andof the activation energy suggest that the growth of the aW platelets obeys a mixed mode combining thevanadium diffusion and a displacive mechanism. Voir les détails
Mots clés : Continuous cooling, KJMA model, additivity rule, diffusion, Displacive mechanism
A Comparative Study of Various Methods of Bearing Faults Diagnosis Using the Case Western Reserve University Data
Bearing is probably one of the most critical components of rotating machinery. They are employed to guide and support the shafts in rotating machinery. Therefore, any fault in the bearings can lead to losses on the level of production and equipments as well as potentially unsafe. For these reasons, the bearing fault diagnosis has received considerable attention from the research and engineering communities in recent years. The purpose of this study is to review the vibration analysis techniques and to explore their capabilities, advantages, and disadvantage in monitoring rolling element bearings. Voir les détails
Mots clés : Vibration analysis, bearing Fault diagnosis, Temporal analysis, Cepstrum analysis, Envelope analysis, Wavelet transform
Contribution to Reconfigured Multi-Level Inverter FedDouble Stator Induction Machine DTC-SVM Control
The Dual Stator Induction Machine (DSIM) meets well with the need for high power applications. In the recent years, it has been increasingly used for variable speed drives. However, its control strategy is still a subject of research due to its complex structure, though it offers more reliable application in use due to the presence of double stators. The fault detection and localization in an inverter are profitable for better diagnosis and the inverter reconfiguration is the most required process to ensure acceptable service continuity. This paper tackles, on the one hand, a control strategy based on the Direct Torque Control combined with the Space Vector PWM of a DSIM (DTC-SVM-DSIM) and on the other hand, a three-level inverter fault detection and localization, reconfiguration of the inverter when operating under open-circuit IGBT switch faults. Several results are presented to illustrate the enhancement of torque and flux quality owed to the proposed control strategy and also to show the improvement of the open-circuit fault detection and localization method for better diagnosis as well as the inverter reconfiguration impact on the drive system service continuity. Voir les détails
Mots clés : DSIM, Multi-level Inverter, NPC, DTC, SVM, Reconfiguration
IMPROVING WEAR PROPERTIES OF HIGH-CHROMIUM CAST IRON BY MANGANESEALLOYING
High-chromium cast irons are widely needed by severalindustrial areas where wear is the dominant environment.They are used in mining, cement- and steel-making plants,and many others. Their microstructure consists of nettedeutectic carbides embedded in an austenitic or martensiticmatrix. The wear behaviour is mainly controlled by thecarbides shape and also matrix type. Several scientificworks try to improve the wear behaviour and to optimizethe life service of this cast iron by using various techniques.In this work, we intend to study the effect of manganesecontent on the microstructure properties and wearbehaviour of a 15 % chromium white cast iron used forball mill production. The present work treats the wearbehaviour, after heat treatment, of a manganese-alloyedhigh-chromium cast iron. A set of specimens were melted inan induction oven by varying the manganese content in therange 0–3 %. Heat-treated samples were analysed byoptical microscopy, MEB (SEM) scanning electronmicroscopy, differential scanning calorimetry, and X-raydiffraction and were wear tested by abrasion and friction.Increasing the manganese addition gave a structural evolutionand a wear resistance improvement. The best wearbehaviour is obtained with samples containing 3 % Mn. Voir les détails
Mots clés : Chromium cast iron, carbide-forming elements, eutectic carbides, secondary precipitation, abrasion, friction