Sciences des matériaux

Nombre total de résultats :476
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Effet du traitement de vieillissement sur l’évolution microstructurale et le comportement électrochimique des aciers inoxydables 2101, 2205 et 2507.

F.Z.ROUIBI  (2021)
Mémoire de Master

this work, the effect of ageing treatment on the microstructural evolution, morphology and potential distribution of LDX2101, SDX2205 and SDSS 2507 stainless steels is investigated. The heat treatment is carried out in two stages: solution treatment for one hour, then water quenching followed by ageing at 750°C for 2101 and 850°C for 2205 and 2507, for 24 hours holding time. Metallographical characterization is conducted using optical microscopy and scanning electron microscopy (SEM) as well as XRD analysis to identify the phases and precipitates formed after treatment. In order to study the effect of ageing on the morphological changes, magnetic behavior and potential distribution on the surfaces of the treated steels, different modes of atomic force microscopy (AFM) are used. The results showed a clear increase in roughness with a very heterogeneous potential distribution due to microstructural changes as a result of the formation of precipitates and secondary phases Voir les détails

Mots clés : LDX2101, SDX2205, SDSS 2507 stainless steels, The heat treatment

Structural, Magnetic, Dielectric and Piezoelectric Properties of Multiferroic PbTi1−xFexO3−δ Ceramics

Khiat Abd elmadjid, Felicia Gheorghiu, Mokhtar Zerdali, Ina Turcan, Saad Hamzaoui  (2021)
Publication

PbTi1−xFexO3−δ (x = 0, 0.3, 0.5, and 0.7) ceramics were prepared using the classical solid-state reaction method. The investigated system presented properties that were derived from composition, microstructure, and oxygen deficiency. The phase investigations indicated that all of the samples were well crystallized, and the formation of a cubic structure with small traces of impurities was promoted, in addition to a tetragonal structure, as Fe3+ concentration increased. The scanning electron microscopy (SEM) images for PbTi1−xFexO3−δ ceramics revealed microstructures that were inhomogeneous with an intergranular porosity. The dielectric permittivity increased systematically with Fe3+ concentration, increasing up to x = 0.7. A complex impedance analysis revealed the presence of multiple semicircles in the spectra, demonstrating a local electrical inhomogeneity due the different microstructures and amounts of oxygen vacancies distributed within the sample. The increase of the substitution with Fe3+ ions onto Ti4+ sites led to the improvement of the magnetic properties due to the gradual increase in the interactions between Fe3+ ions, which were mediated by the presence of oxygen vacancies. The PbTi1−xFexO3−δ became a multifunctional system with reasonable dielectric, piezoelectric, and magnetic characteristics, making it suitable for application in magnetoelectric devices. Voir les détails

Mots clés : dielectric response, Fe-doped PbTiO3, Magnetic Properties, multiferroic ceramics, piezo- electric properties

Influence of isothermal aging in LDX 2101 duplex stainless steel on the microstructure and local properties

N Ouali, B Cheniti, B Belkessa, B Maamache, R Kouba, M Hakem  (2021)
Publication

In the present work, the interface morphology and the evolution of nitride precipitates in LDX 2101 stainless steel isothermally treated at 750 °C for various aging times were investigated. The microstructure results showed that the Cr2N nitrides precipitated along the δ/γ interface with 200 nm in length and continue to grow to 2 μm after 240 h of aging. However, only Cr2N nitrides were found at the δ/δ interface after long term of aging. Atomic force microscopy (AFM) analysis revealed that Cr2N nitrides andCr23C6 carbides started to precipitate after the first 10 min of aging with a small needle shape of the former and specific triangular morphology of the latter. The evolution of hardness and Young’s modulus of the interfaces, performed with nano-indentation measurements, showed that the δ/γ interface became harder (4.1 ± 0.2 GPa) with increasing aging times, whereas negligible changes in the hardness and elastic modulus were recorded at the δ/δ interface. 3D topographic analysis of the immersed surfaces revealed that the susceptibility of δ phase to preferential dissolution in 3.5% NaCl solution increased with aging time. This behavior was manifested by the important imperfections of δ phase, the high surface roughness (55.7 nm), and the deep corrosion pits (30 nm) along the δ/γ interface and around the Cr2N nitrides. Voir les détails

Mots clés : microstructure, Interface, precipitates, Nano-hardness, Surface degradation

Effect of heat treatment on microstructure and tribological behavior of friction stir processed Al2O3-reinforced AA2024-T351 matrix

Adel Haddad, Abdessabour Benamor, Nabil Chiker, Youcef Hadji, Mustapha Temmar, Maamar HAKEM, Riad BADJI, Said ABDI, Mohamed HADJI  (2021)
Publication

In the present work, 2024-T351 Al alloy reinforced with alumina particulates (Al2O3p) was elaborated using friction stir processing (FSP). The effect of solution heat treatment followed by subsequent aging on microstructure, hardness, and tribological behavior is discussed. It was noticed that the hardness of the as-FSPed 2024-T351/Al2O3p was slightly enhanced in comparison to the as-received AA2024-T351 material, whereas the resulting wear resistance was remarkably improved. After heat treatment process, the composite volume increased, and swelling and pores were created at the processed area. The heat treatment caused a degradation in wear resistance compared to as-FSPed composites. The precipitation mechanism changed forAA2024/Al2O3p; reactions occurred at grain boundaries between Al2O3 and Cu or Mg, causing their depletion from the Al matrix. Intriguingly, the precipitation mode in heat-affected zone of the matrix also changed to grain boundary precipitation. Voir les détails

Mots clés : Friction stir processing, Metalmatrix composites, wear, friction

Pressureless sintering and tribological properties of in-situ TiC-Ni3(Al,Ti)/Ni(Al,Ti) composites

Nabil Chiker, Abdessabour Benamor, Adel Haddad, Youcef Hadji, Maamar HAKEM, Riad BADJI, Mohamed Labaiz, Mohamed Azzaz, Mohamed HADJI  (2021)
Publication

In this study, we report on the microstructure and tribological characterization of in-situ TiC and γ’-Ni3(Al,Ti)reinforced γ-Ni(Al,Ti) matrix composites, synthesized by in-situ reaction of Maxthal211 (Ti2AlC-Ti3AlC2, MAX phase) and Ni precursors. Three composites were elaborated from 10, 20 and 30 wt % of the MAX phase precursor which fully reacted with Ni-matrix at 1080 °C sintering temperature for 4 h; the MAX phase decomposed into TiC, and the released Al and Ti atoms diffused in Ni matrix forming γ-Ni(Al,Ti) solid solution and γ’-Ni3(Al,Ti)intermetallic. Scanning Electron Microscopy (SEM), X-Rays Diffraction (XRD) and Raman spectroscopy were used to study the different microstructures and worn surface characteristics. Dry sliding properties of the composites under different normal loads were studied using a ball-on-disc tribometer. Addition of 10 wt % MAX phase procured the highest hardness (1.35 GPa) which is two times higher than that of pure Ni. Whereas all there inforced composites exhibited better wear resistance. The formation of a lubricious layer during sliding and the good in-situ bonding between Ni/reinforcement phases, were the main cause to the enhanced wear resistance. Voir les détails

Mots clés : Metal matrix composites, Pressureless sintering, MAX phase, diffusion, In-situ composites, wear

Effect of Environmental Media on the ElectrochemicalBehavior of API X70 Pipeline Steel

A. GHARBI, B. Benayad, O. Assala, K. BOUHAMLA, O. GHELLOUDJ, S. Chettouh, S. REMILI, A. Bachiri  (2021)
Publication

This work investigates the corrosion behavior of X70 steel in different environments: sea sand, desert sand, mud, and seawater. The principle of extracting solutions from these media consisted of mixing a soil material with distilled water, and the mixture was agitated using an automatic agitator, which resulted in the extraction of the solution. Potentiodynamic polarization and electrochemical impedance tests are used to characterize the samples in both media. The results show that the pipeline steel X70 has an excellent corrosion resistance in the sea sand solution, resulting in a low corrosion current density compared to other media. The impedance diagrams for both media are characterized by two capacitive loops, the first loop is attributed to charge transfer processes and the second loop is related to diffusion phenomena. The observation of corroded surfaces shows that the corrosion mechanism in different media is by pitting. Voir les détails

Mots clés : pitting, sea sand, seawater, corrosion

Etude mécanique et microstructurale des soudures des alliages d'aluminium soudées par friction

S. BENDOUMA, G.GUERMAT  (2020)
Mémoire de Master

This work is related to the study of the friction welding process. This type of welding has many applications in different branches of industry. This process has many advantages. First, the very high quality assemblies can be made. In addition, this process is much faster than any other conventional processes. Furthermore, it can be completely automated so that constant quality is guaranteed. The aim of this study is the optimization of the parameters of friction welding: (by varying the friction time [s] and the rotational speed [rpm], forging time [s] and the friction pressure and forging [MPa] remain constant). An experimental procedure was used to obtain a welded junction (alu-alu), the alloy used is Al 6013-T8. We used several characterization methods, simple but effective and suitable for this kind of research work; such as microstructural characterization by optical microscope and mechanical characterization namely microhardness and tensile testing. We observed that the microstructure has three zones (TMAZ, HAZ and MDZ), The microhardness profile has a certain homogeneity and the tensile tests have shown that the tensile strength, elongation and elastic limit increase with increased friction time. In general, the mechanical properties are influenced by the overall effect of the metallographic structure of the weld. The latter is closely linked to the process parameters. Voir les détails

Mots clés : Friction welding, 6013-T8 alloy, Welded joint, mechanical properties, microstructure, Microhardness

Comportement mécanique et métallurgique des jonctions hétérogènes soudées par friction rotative

A. CHERIFI, R. BELHOCINE  (2020)
Mémoire de Master

Rotational friction welding is a solid state welding process, which has seen spectacular development in various industries. It offers the possibility of producing very high quality solder joints in an extremely short time. The objective of this work is to improve the operating parameters of this process by changing the friction time (periods) and fixing the other parameters namely the speed of rotation [round per minute], the forging time [s], the friction and forging pressure [MPa]. The major problem with the disimmilar assembly of aluminum and stainless steel alloys is the low mechanical strength in the welded joint, due to the formation of certain unwanted inter-metal compounds during welding. An experimental procedure was used to obtain an Al6013-T8 /304L stainless steel welded joint with and without copper insertion. Different characterization methods were used namely x-ray diffraction, optical microscopy, HV microhardness and tensile testing. The Al6013-T8 side microstructure reveals the formation of two zones, the HAZ and the TMAZ at the center of the junction, unlike 304L stainless steel, which has not undergone any mechanical deformation. The microhardness of Al6013-T8 increased in the vicinity of the junction, and tensile testing revealed that the mechanical characteristics of the joints increase with increasing friction time. Voir les détails

Mots clés : Rotational friction welding, the speed of rotation, the forging time

Elaboration et caractérisation des couches minces de matériau CZTS (Cu2ZnSnS4) obtenues par voie sol gel : Applications a la photovoltaïque

BENACHOUR Med Cherif (2020)
Thèse de doctorat

Récemment, un travail considérable a été fait sur le semi-conducteur de composé quaternaire Cu2ZnSnS4 (CZTS), en raison de sa simplicité, son faible coût et surtout sa souplesse dans la combinaison de plusieurs composés chimiques, pour en faire une bonne couche absorbante pour les cellules solaires à couches minces et générateur d'énergie thermoélectrique. Les couches minces CZTS sont une sorte de semi-conducteur à bande interdite directe de type p avec une valeur de bande interdite de Eg ≈ 1,5 eV pour la conversion d'énergie photoélectrique et sont caractérisés par un grand coefficient d'absorption (> 104 cm− 1). De cette manière, le but du présent travail est d'étudier les paramètres de la température de recuit et la durée de recuit optimale pour la formation de couche mince CZTS pur. Pour cela, nous avons développé un procédé simple et non toxique sans sulfuration utilisant le procédé sol gel et les voies de vide pour préparer les couches minces de phase CZTS pure déposés sur des substrats en verre par la technique de dip-coating et recuits à différentes température et avec de durées différentes. Nos avons étudié l'effet de la température de recuit sur les propriétés optiques des couches minces CZTS. Ces dernières ont été déposées par technique de dip-coating utilisant la méthode sol-gel. Nous avons constaté que l'augmentation de la température de recuit de 200 à 500 °C pendant une heure réduit la bande interdite d'énergie de 1,72 à 1,50 eV. Ainsi, ils nos jugé que ces couches minces sont bons pour les cellules solaires. Ainsi, la considération de ces résultats nous a incités à étudier l'effet de la durée de recuit de 5 à 60 min sur les propriétés des couches minces CZTS. Les échantillons obtenus ont été étudiés par plusieurs techniques telles que la XRD, la spectroscopie Raman, la SEM, Microscopie à force atomique (AFM), la spectroscopie UV-vis et la photoluminescence. Confirmée par spectroscopie Raman, l'analyse XRD révèle la formation d’un composé monophasé Cu2ZnSnS4, de composition quasi-stoechiométrique, dans la structure tétragonale de kestérite avec une orientation préférentielle le long de la direction [112]. La taille des grains a tendance à augmenter à mesure que la durée du recuit augmente et la température du recuit augmente aussi, ce résultat confirmé par SEM. L’étude de la morphologie par le MEB et l’AFM confirme que les films minces, ainsi élaborés sont homogènes, sans fissuration, de structure nanométrique et possédant une très faible rugosité (de l’ordre de 1 nm).L'analyse des mesures optiques montre que ces couches minces ont un coefficient d'absorption relativement élevé dans le spectre visible avec une réduction de bande interdite de 1,62−1,50 eV, ce qui est assez proche de la valeur optimale pour une cellule solaire. La photoluminescence (PL) distingue des bandes larges qui ont des maximums d'intensité limités entre 1,50 et 1,62 eV, correspondant à la bande interdite optique du CZTS. et limités augmentant avec l'augmentation de temps de recuit.L'étude des propriétés électriques à l'aide de la méthode de deux points (I=f(V)) a également montré que l'augmentation du temps de recuit améliore les propriétés électriques de la structure.De plus, l'étude a abordé le problème des phases secondaires et a suggéré une voie pour éviter leur sa formation. Voir les détails

Mots clés : CZTS, Dip-Coating, sol gel, DRX, Cellule solaire.

Étude et réalisation de structure pérovskite non stœchiométrique PbTiO3-δ pour des applications ferroélectriques

KHIAT Abdelmadjid (2020)
Thèse de doctorat

Dans ce travail de recherche, nous avons élaboré le matériau PbTiO3-δ à partir les oxydes PbO et Ti3O5 en utilisant  la technique réaction à l’état solide dans un four sous vide. Dans ce travail nous avons étudié trois paramètres, le premier c’est l’effet de la température de calcination sur les propriétés structural (DRX, FTIR, RAMAN, EDX), microstructural (MEB) et magnétique (VSM) de PbTiO3-δ et étudié les propriétés diélectrique (pont d’impédance) de matériau élaboré. Dans l’objectif d’amélioration des propriétés magnétique de PbTiO3-δ, dans la deuxième partie nous avons dopé le PT avec un matériau ferromagnétique Fe d’où nous avons varié la quantité de dopant Fe et étudié l’effet de dopage sur les diffèrent propriété structural, microstructural, diélectriques et magnétiques. Dans la troisième partie nous avons étudié l’effet de la pression de vide de calcination sur les différentes propriétés structurales, microstructural, diélectriques et magnétiques de PbTiO3-δ élaboré par la technique réaction à l’état solide Voir les détails

Mots clés : PbTiO3-δ, Pérovskite, Lacune d’oxygène, Aditifs, DRX, MEB, Raman, Echographies ultrasonore, Relaxeur.