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N.Dilmi, N-E.Bacha, A.Younes  (2020)

This work aims to study the effect of mechanical milling of Fe, ZnO, and Ni elemental powders andthermal spraying processes on chemical composition, structural properties, and magnetic behaviorof the Fe60–xNix(ZnO)40 coatings. As the first step, the FeNi/ZnO composite was synthesized bymechanical alloying process, and afterward, the milled powder was coated by a thermal sprayingtechnique on a steel substrate. Obtained samples were characterized by the methods of X-raydiffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS),atomic force microscopy (AFM), and with help of vibrating sample magnetometer (VSM). Aftermechanical milling, the crystallite size of the powder decreased from 18 to 10 nm, while the latticestrain increased from 0.31 to 0.59%, and a new solid solution FeNi formed after 20 h of milling dueto diffusion of nickel into the iron lattice. After the thermal spraying process, different phasesappeared in a surface coating such as ZnFe2O4, NiFe2O4, and FeNi. The magnetic and structuralproperties of the coated powders are influenced by the change in chemical composition. Thus, theincrease of Ni concentration improved the soft magnetic performance of the coating significantly.The highest saturation magnetization was determined in Fe40Ni20(ZnO)40 sprayed powder. However,the smallest coercivity appeared in Fe50Ni10(ZnO)40 sprayed powder. Voir les détails

Mots clés : FeNi/ZnO nanoparticle coating, Mechanical Alloying, Thermal Spraying, magnetic behavior, Structural properties

Synthesis of Lead-Free Ceramicsof the Perovskite Type for PiezoelectricApplications by Conventional Solid-StateReaction

K. Sedda, R. Djafar, K. Boumchedda, F. Boukazouha, M. Latef  (2020)

Structural properties of BaTiO3, CaTiO3 and Ba0.85Ca0.15Ti0.9Zr0.1O3 prepared by conventional solid state reaction technique, at different calcinations temperatures 1100, 1150 and 1280 °C and sintering temperatures (1200and 1300 °C) are studied. These compositions were selected because of theirinteresting piezoelectric properties. To follow the decomposition process of theprecursor, a differential thermal analysis coupled with thermogravimetric analysis (ATG-ATD) was performed. Structural parameters are analyzed by X-raydiffraction (XRD) and scanning electron microscopy (SEM). The obtained resultsshowed clearly the synthesis of the perovskite phase. The diffractogram illustratesthat BCTZ symmetry is both cubic with a Pm-3 m space group and orthorhombic with a R3m space group, the calculated phase rates are respectively 10% and90%. The results allowed us to specify the effect of sintering temperatures on thestructural properties of ceramics. Voir les détails

Mots clés : Lead free ceramics, synthesis, ;, microstructure, Perovskite

Cu2O addition and sintering temperature dependence of structural,microstructural and dielectric properties of CaCu3Ti4O12 ceramics

R. Djafar, K. Boumchedda, A. Chaouchi, D. Fasquelle, K. Sedda, S. Brahimi, K. Khalfaoui, M. Bououdina  (2020)

This study is aimed in the replacement of commonly used (CuO) by Cu2O in the synthesis of perovskiteCaCu3Ti4O12 (CCTO) phase by the solid-state reaction method. The XRD analysis of powder calcined at 1100 ?Cand ceramics sintered at different temperatures show that the CCTO phase was well crystallized with thepresence of small quantities of additional phases. The SEM/EDS analysis of prepared pellets show that the formation of Cu2O/CuO phase occurs above 950 ?C, resulting in enhanced densifcation at 1050 ?C (>96%).However, it is found that the Cu2O-based CCTO begins to degrade around 1090 ?C. The densifcation aftersintering at 1050 ?C reaches 96%, meanwhile dielectric constant and loss tangent values are optimum in the lowfrequency range (<103 Hz); i.e. 13378 and 0.177, respectively. This favors the use of Cu2O instead of CuO inCCTO ceramics for applications at low frequencies. Voir les détails

Mots clés : Ceramics, CCTO, powder metallurgy, XRD and SEM, Dielectric properties

Particle Swarm Optimization of Fuzzy Fractional PDµ+I Controllerof a PMDC Motor for Reliable Operation of Wire-Feeder Units ofGMAW Welding Machine

N. Hamouda, B. Babes, S. Kahla, C. HAMOUDA, A. Boutaghane  (2020)

In this article, we consider the development of an optimal control approach based on fuzzy fractional PDµ+I controller to improve thespeed error-tracking and control capability of a permanent magnet DC Motor (PMDC) driven wire-feeder systems (WFSs) of gas metal arc welding(GMAW) process. The proposed controller employs an optimized fractional-order proportional derivative + integral (PDµ+I) controller that serves toeliminate oscillations, overshoots, undershoots and steady state fluctuations of the PMDC motor and makes the wire-feeder unit (WFU) has fast andstable starting process as well as excellent dynamic characteristics. The fixed controller parameters are meta-heuristically selected via a particleswarm optimization (PSO) algorithm. Numerical simulations are performed in MATLAB/SIMULINK environment and the performance of the proposedfuzzy fractional PDµ+I controller is validated. The simulation tests clearly demonstrate the significant improvement rendered by the proposed fuzzyPDµ+I controller in the wire-feeder system's reference tracking performance, torque disturbance rejection capability and robustness against modeluncertainties. Voir les détails

Mots clés : GMAW process, Wire-feeder System (WFS), fuzzy fractional PDµ+I controller, Particle Swarm Optimization (PSO) algorithm

Temperature Evolution, Microstructure and Mechanical Properties of Heat-Treatable Aluminum Alloy Welded by Friction Stir Welding: Comparison with Tungsten Inert Gas

Saliha Gachi, Mouloud Aissani, Fouad Boubenider  (2018)

Friction Stir Welding (FSW) is a solid-state welding technique that can join material without melting the plates to be welded. In this work, we are interested to demonstrate the potentiality of FSW for joining the heat-treatable aluminum alloy 2024-T3 which is reputed as difficult to be welded by fusion techniques. Ther eafter, the FSW joint is compared with another one obtained from a conventional fusion process Tungsten Inert Gas (TIG). FSW welds are made up using an FSW tool mounted on a milling machine. Single pass welding was applied to fabricated TIG joint. The comparison between the two processes has been made on the temperature evolution, mechanical and microstructure behavior. The microstructural examination revealed that FSW weld is composed of four zones: Base metal (BM), Heat affected zone (HAZ), Thermo-mechanical affected zone (THAZ) and the nugget zone (NZ). The NZ exhibits a recrystallized equiaxed refined grains that induce better mechanical properties and good ductility compared to TIG joint where the grains have a larger size in the welded region compared with the BM due to the elevated heat input. The microhardness results show that, in FSW weld, the THAZ contains the lowest microhardness values and increase in the NZ; however, in TIG process, the lowest values are localized on the NZ. Voir les détails

Mots clés : Friction Stir Welding, tungsten inert gaz, aluminum, microstructure

Weldability, microstructure, and residual stress in Al/Cu and Cu/Alfriction stir spot weld joints with Zn interlayer

Adel Boucherit, Said ABDI, Mouloud Aissani, Brahim MEHDI, Khadidja Abib, Riad BADJI  (2020)

In this work, the effect of lap joint configuration and Zn interlayer addition on the microstructure, the residual stress state, and thequality of Al/Cu (configuration #1) and Cu/Al (configuration #2) friction stir spot welds (FSSW) was investigated. The studyrevealed the close dependency of the weld joint quality on the pin length and Zn addition. The higher the pin plunge depth is, thegreater the obtained tensile shear strength. The Zn addition reduced sensibly the thickness of Al2Cu layer (from 10 to 2 μm) andfavored the formation of the Al4.2Cu3.2Zn0.7 precipitate that hindered the formation of detrimental Al4Cu9compounds. Materialflow analysis revealed the presence of an intermixing zone containing thin continuous intermetallic layer (approximately 2.07 μm) at the weld interface of configuration #1. Meanwhile, the Cu material was covered by the Zn layer, which resultedin a hardness increase (228 HV) at the stirred zone. In addition, a significant increase of the tensile shear strength from 1650 to 3600 N was noticed (an improvement rate of ≈ 118%). Conversely, in configuration #2, the Zn foil was squeezed out of the spotweld interface resulting in the absence of material intermixing, discontinuous intermetallic layer, low hardness level (140 HV),and weak improvement rate of the shear strength (≈ 53%). The Zn interlayer addition resulted in a quasi-symmetric distribution ofthe residual stresses and shifted their nature from tensile stresses (+ 60 MPa) to compressive ones ( − 10 MPa). Voir les détails

Mots clés : FSSW, aluminum, copper, Zinc interlayer, Tensile shear, microstructure, intermetallic Compounds, residual stress

CoSoTIA Project: Decision Support for the Choice of Concentrated Solar Technologies for Electricity Generation

M. AISSANI, K. Mohammedi, A. ZITOUNI, M. BOUKRAA, T. CHEKIFI, A. Mehiris  (2020)

The C oSoTIA (Concentrated Solar Technologies for I ndustrial Appli-cations) project initiated by the CRTI center in collaboration with the URMPEunit concerns the s tudy and development of CSP s olar concentrators f or indus-trial applications. I n t he present work, we present decision s upport t ools f or thechoice of a s olar concentration t echnology for s ites i n Algeria. T hey will be usedfor t he comparison between diff erent t echnologies of solar concentration e.g.:cylindro-parabolic, parabolic, s olar tower, etc. T he models used include projectcosts and site characteristics; they incorporate also engineering knowledge (eco-nomic, social, t echnical and environmental). The i nformation needed for decision-making produced by these t ools i s: the t otal cost of the project, i ndicators witheconomic, social, t echnical and environmental aspects. The case s tudies presentedwere conducted under t he SAM Advisor environment, which was developed t oevaluate the capacities t o i mplement C SP project i n order to produce expertisefor t he diff erent actors t hrough an application on a given s ite (by t he client). Fourcase sites i n Algeria and f or two t ypes of s olar concentrator plant are studied andpresented. A comparative study was conducted and for each s ite the best C SP wasdeduced and commented. Voir les détails

Mots clés : Decision support, Multicriteria analysis, Solar concentration, CSP, SAM Advisor

The Microstructure, Texture and Mechanical Propertiesof Friction Stir Welded Aluminum Alloy

Saliha Gachi, Mouloud Aissani, Thierry Baudin, Anne.Laure Helbert, François Brisset, Sébastien Gautrot, Marie-Hélène Mathon, Djamel Bradai, Fouad Boubenider  (2020)

The microstructure and texture of 7075-T6 FSW weld with optimal parameters are investigatedusing optical microscopy, electron back scatter diffraction and neutron diffraction. The mechanical proper-ties are characterized through microhardness, nanoindent ation and ultrasonic tests. The friction stir weldingis performed at a nominal rotational speed of 1400 rpm and a traverse speed of 60 mm/min. The nugget zonecontained fine, equiaxed and fully recrystallized grains. The texture of the base material mainly consisted ofCube and rotated Goss components. However, in the nugget zone, the dominant texture components were Band among common shear orientations. Elastic modulus was measured by ultrasonic and nanoindentationmethods. The ultrasonic method being nondestructive, easy, inexpensive and fast. It is found that a littleincrease of Young modulus is observed in nugget zone compared to base metal. Voir les détails

Mots clés : Aluminum alloy, FSW, microstructure, texture, Microhardness, Young modulus

Effect of annealing temperature on the microstructureevolution, mechanical and wear behavior of NiCr–WC–CoHVOF-sprayed coatings

Azzeddine Mazouzi, Boubekeur Djerdjare, Salim Triaa, Amine REZZOUG, Billel CHENITI, Samir M. Aouadi.  (2020)

In the present work, the effect of annealing temperature on the microstructure, mechanical and tribological properties of NiCr–WC–Co coatings produced by the high-velocity oxy-fuel (HVOF) technique has been investigated. X-ray diffraction and scanning electron microscopy revealed the dissolution of WC into the NiCr matrix to form W2C and Cr3C2 with the annealing process. This dissolution became complete at 800 °C. The mechanical properties of the coatings were investigated using nano-indentation and Vickers fracture toughness measurements. These measurements suggested that the hardness, Young’s modulus, and fracture toughness values increased because of the newly formed carbide phases as a result of the dissolution of the WC particles.The overall properties of the coatings were found to be optimum for annealing temperatures of 800 °C. The wear mechanism appears to be abrasive in the as-sprayed coating, and it becomes a combination of an abrasive and oxidative wear with increasing the annealing temperature Voir les détails

Mots clés : HVOF;, WC coating:, Annealing;, Wear resistance;, Nano-indentation

Structural, microstructural and thermal characterization of Fe- doped ZnO powder nanostructures prepared by mechanical alloying

oudjertli salah, Bensalem Rachid, Alleg Safia, J J Suñol, Mohamed Bououdina  (2017)

ZnO powder nanoparticles mechanically alloyed were doped with iron to investigate their structural and microstructural properties using X-ray diffraction (XRD) and differential scanning calorimetry (DSC) for examined 1% Fe doped ZnO. The ZnO starting pure powder exhibited a hexagonal crystal structure with space group p63mc of ZnO, however with the introduction of 1% Fe in the ZnO milled powder, the hexagonal ZnO phase remained unchanged, whereas the microstructural parameters were subject to significant variations due to the introduction of Fe atoms into the ZnO hexagonal matrix to replace oxygen ones. The size of crystallites and microstrains are found milling time dependent. Voir les détails

Mots clés : ZnO, XRD, DSC