Sciences des matériaux

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Effet des Additiond ternaires et evolution des défauts ponctuels en fonction de la temperature dans les alliages FeNb et FeZr

L. Rabahi, D. Bradai, A. Kellou  (2009)
Article de conférence

Les intermétalliques sont des composés prometteurs qui suscitent un grand intérêttechnologique. Ces matériaux allient des propriétés mécaniques élevées à hautes températureset une assez bonne résistance à l’oxydation. Cependant leur utilisation est limitée par leurfragilité à basses températures. Ce qui incite les métallurgistes à introduire des élémentsd’additions pour améliorer leurs caractéristiques physiques.Ce travail consiste à déterminer la concentration des défauts ponctuels en fonction dela température en utilisant le model Wagner Schottky. Les énergies de formation desdifférents types des défauts sont calculées en utilisant une méthode Ab initio basée sur laméthode du pseudopotentiel et sur la base des ondes planes.Les calculs ont été faits pour deux alliages FeNb et FeZr cristallisant dans la structureB2. Les énergies de préférence de site des éléments d’addition Ti, V, et Cr sont calculées ainsique les différents paramètres structuraux tels le paramètre de maille, le module decompression et les énergies de formation. Voir les détails

Mots clés : Intermetalliques (IMC), FeNb, FeZr, défauts ponctuels, ab initio, Modéle de Wagner-Schottky

Ageing Behavior and Restoration by Heat Treatments of 2205 Duplex Stainless Steel

Naima Ouali, Brahim BELKESSA, Mabrouk BOUABDALLAH  (2013)
Article de conférence

Duplex stainless steels (DSS) are prone to intermetallic phase formation at high temperatures, which can drastically decrease the toughness property. This work investigates the microstructural evolution of σ phase in a SAF 2205 DSS after subsequent isothermal aging and annealing treatments and there influences on mechanical properties. We submit specimens to impact testing and hardness measurements before and after ageing and restore treatments. The results showed that considerable changes in term of precipitation of intermetallic particles were observed in microstructure. The formation of these intermetallic phases such as σ was recognized as the major reason for the observed changes. However aging at 850°C led to a significant decrease in toughness and slight increase in hardness and the high temperature treatment at 1080°C dissolves all secondary phases.. Voir les détails

Mots clés : duplex stainless steel, ageing, Restore, Toughness, sigma Phase

Theoretical study of structural and thermalproperties of Fe2 (Zr, Nb) Laves alloys

L. Rabahi, A. Kellou, Bradai  (2010)
Article de conférence

The aim of this is to use ab initio calculations(with the (PP) Pseudopotential method) to give newinsights on structural and thermal properties ofbinary and ternary C15-Laves Fe2(Zr,Nb) alloys. Thetemperature effects have been obtained using thequasi-harmonic Debye model exploiting the totalenergy calculations of the PP method. The main results show that:The structural properties obey to the Vegard’s law,meaning that Fe2(Zr, Nb) are quite ordered alloysindependent of the Zr/Nb ratio. In addition, The use of the quasi-harmonic Debye model wassuccessfully applied to determine the thermalproperties of the Fe2(Zr, Nb) alloys in the 0-1000 Ktemperature range. The effect of temperature on bulkmodulii and volume expansions is important inFe2Nb while lesser in Fe2Zr. Voir les détails

Mots clés : Laves Phases, First-Principles calculations, DFT, Quasi-Harmonic Approximation, Debye's Model, Thermal Properties

Structure and stability of Fe2(Zr1-xNbx) Laves Phases

L. Rabahi, A. Kellou, D. Bradai  (2012)
Article de conférence

The Laves phase structures (C15, C14 and C36) exist in a large number of binary andternary intermetallic compounds of composition AB2. Although they are well known sincelong time ago, there are still unsolved problems concerning the stability of the respectivecrystal structures. Therefore, it is difficult to predict which of the three structure types is thestable one for a given laves phase compound. In this sense, several calculation methods havebeen successfully applied to predict the stable ground state structure of various laves phases,but these calculations are restricted to the stoichiometric compositions and at 0 K. However inreal systems the stability of laves phase type is a function of temperature and composition andalso different Laves phases types may coexist in a single system. This is the subject of thepresent work, where we applied the quasi harmonic approximation implemented on Gibbs2program and the Ab initio pseudopotential method to study the temperature and composition-dependence transformations in the Laves phase Fe2(Zr1-x,Nbx) system. The results show acomplex behavior with a cyclic variation of the stable structure types as function oftemperature and Niobium concentration. Voir les détails

Mots clés : Laves Phases, First-Principles calculations, Stability, Heat of Formation, Thermal Properties and Gibbs2 Program

Finite element modeling and analysis of electromagnetic field distribution for different shapes of metallic materials

Salim Bennoud, Mourad ZERGOUG  (2014)
Article de conférence

In aeronautical industry, diversity of used materials, dimensions and complexity of the parts require a specific treatment in order to fulfilling the requirements of safety and reliability.In this paper, electromagnetic problem modeling is developed in order to realize a data-processing application able to calculate electromagnetic field distribution in different mediums especially those used in aeronautics.The finite element method is successfully applied since it adapts for any selected section. The numerical results enable to determinate the field values in any point of the chosen geometry and to determine thereafter the system parameters as well as the distribution of energy. Geometry dimensions, material properties and used frequency influence on results. And for the special cases these results are compared with those given by FEMLAB code. The results are very similar with a good precision which enables usage of the developed code to carry out simulations for other geometries of materials with different proprieties. Voir les détails

Mots clés : Electromagnetic interaction, Maxwell's equations, aeronautical materials, Finite Element Method, field distributions, FEMLAB

Etude ab initio des propriétés Structurales, Magnétique etStabilité du système Fe2(Zr,Nb) dans les trois phases de Laves:C14 C15 et C36.

L. Rabahi, A. Kellou, B. Alili  (2014)
Article de conférence

The pseudopotential method (PP) Based on Density Functional Theory (DFT), using theGeneralized Gradient Approximation (GGA) was applied to investigate the Fe2(Zr,Nb)system within the three Laves phases structures: Cubic C15, Hexagonal C14 and C36. Theeffects of Nb concentration on structural, magnetic and stability of the system were studied.The lattice parameters, bulk modulus and magnetic moments of the three phases werepredicted and showed a significant dependence on Nb concentration. We evidenced therigidity of the Fe2Nb was higher than the Fe2Zr one for C15, C14 and C36. The energeticphase diagram of the systems was also established by determining the heat formation and thestability of the alloys was discussed accordingly. The obtained results showed that the Lavesphase have close formation energies which suggests that the C15, C14 and C36 phases canco-exist at low-temperature. In addition, the magnetic behavior was also established and themagnetic moments were found to be on Fe atoms. Consequently, these alloys were predictedto be ferromagnetic for all phases. The obtained results were in good agreement with availabletheoretical and experimental ones. Voir les détails

Mots clés : Laves Phases, Pseudopotential Method, DFT, Heat of Formation, Stability

Structural and thermal properties of Fe2(Zr,Nb) system in C15, C14 and C36 Laves phases:First-Principles study.

L. Rabahi, D. Bradai, A. Kellou  (2013)
Article de conférence

The pseudopotential method (PP), Based on Density Functional Theory (DFT) using the Generalized Gradient Approximation (GGA) was applied to investigate the Fe2(Zr, Nb)system within the three Laves phases structures: Cubic C15, Hexagonal C14 and C36. The effects ofNb concentration on structural, thermal and stability of the system were studied. The latticeparameters and bulk modulus of the three phases were predicted and showed a good agreement withthe available experimental data. The rigidity of the Fe2Nb was higher than the Fe2Zr one for C15, C14 and C36. The energetic phase diagram of the systems was also established by determining theheat formation of the different phases. The obtained results showed that the Laves phase have closeformation energies which suggests that the C15, C14 and C36 phases can co-exist at low-temperature. Finally, the temperature effect on the structural parameters, thermal expansions, heatcapacities and Debye temperatures are determined from the non-equilibrium Gibbs functions anddiscussed accordingly. Voir les détails

Mots clés : Ab initio calculations, Pseudopotential Method, DFT, Laves Phases, Debye's Quasi-Harmonic Model

Precipitation phenomenon study in austenoferritic steel of 22% chromium and 5% nickel during aging treatment.

Naima Ouali, Mabrouk BOUABDALLAH, Brahim BELKESSA  (2012)
Article de conférence

The aim of this study is to refine the duplex microstructure without using the conventional processes, as the thermo mechanical treatments. The adopted way consists in carrying out and optimizing aging and annealing heat treatments. A preliminary treatment of hardening since 1250°C was applied to increase the proportion of ferrite in the matrix. The treatments of aging were carried out at the temperature of 850°C during variable duration periods from 02h, 10h and 30 hours. The refinement of the grains had mainly on the level of ferrite, this being with the simultaneous germination of ferrite and austenite during the dissolution of the precipitates.. Voir les détails

Mots clés : duplex stainless steel, heat treatment, microstructure, grain refinement

Characterization of a welded joint in steel API.5L.X70 having undergone successive repairs

B. MAAMACHE, M.BOUABDALLAH, H.BRAHIMI, Y. YAHMI, M. NOUREDDINE  (2012)
Article de conférence

The object of this paper is to study the effect of the successive repairs on the weldment quality, knowing that these repairs constitute a main problem in the hydrocarbons transportation industry. We study the effect of several thermal cycles welding on the microstructural welding joints evolution, particularly the heat affected zones and its extend. We weld and repair many times a steel sample used in the hydrocarbons transportation. The metallographic analysis and mechanical tests results show the harmful effect of repairs that cause a prejudice on the life of weldment Voir les détails

Mots clés : welding, Repair, Thermal cycle, Heat affected zone

Etude Microstructurale de l’Alliage nanostructuré (Fe65Co35)70Al30 obtenu par mécanosynthése

BOUTAGHOU Zoheir, Haddad Ahmed, MIROUD Djamel  (2014)
Article de conférence

Des poudres nanostructurés de l’alliage (Fe65Co35)70Al30 sont obtenues par un broyeur à haute énergie sous une atmosphère d’argon. Des variations morphologiques et microstructurale au cours du broyage sont observées par microscopie électronique à balayage (MEB) et par diffraction des rayons X (DRX). La réduction de la taille des cristallites (16–7 nm) est accompagnée par une augmentation des microdéformations du réseau. Une phase ternaire est obtenue après 8 heures de broyage. Voir les détails

Mots clés : Poudres Fe-Co, alliage nanostructuré, Mécanosynthèse, Diffraction des rayons X