Publications internationales

2017
Ahlam Khadraoui; Fatima Zohra Bentayeb. (2017), Ab initio study of hydrogen storage in TiFe intermetallic : Materials Research Express, https://doi.org/10.1088/2053-1591/aa8f64

Résumé:

2016
S. Louidi; F.Z. Bentayeb; S. Tria; J.J. Suñol; L. Escoda. (2016), Structural and thermal study of nanostructured Cr 80 Co 10 Si 10 mixture : Advanced Powder Technology, http://dx.doi.org/10.1016/j.apt.2016.05.030
2015
Ahlem Khadraoui, Fatima Zohra Bentayeb. (2015), First-Principles Study of Hydrogen Storage in Fe-Ti System. Defect and Diffusion Forum : Trans Tech Publications Ltd, https://doi.org/10.4028/www.scientific.net/DDF.365.266

Résumé: In this study, a first-principles investigation of hydrogen storage in the FeTi intermetallic is carried out. The structural and electronic changes due to hydrogen insertion into the FeTi intermetallic are determined using DFT and pseudo-potential calculations through the code SIESTA (Spanish Initiative for Electronic Simulation of Thousand of Atoms). The pseudopotentials are constructed using Troullier and Martins parametrization which describes correctly the ion-electron interactions. To define the real-space grid, necessary for numerical calculations of the electron density, detailed tests were performed in order to choose the appropriate basis set, the energy cutoff and the k-grid cutoff. The exchange-correlation potential is treated with the generalized gradient approximation (GGA). Lattice data, bonding properties and the density of states provide an explanation for the role played by hydrogen in the chemical bond with the Ti and Fe constituents.

2013
H. Laala-Bouali; F.-Z. Bentayeb; S. Louidi; X. Guo; S. Tria; J.J. Suñol; L. Escoda. (2013), X-ray line profile analysis of the ball-milled Fe–30Co alloy. Advanced Powder Technologyhttp://dx.doi.org/10.1016/j.apt.2012.04.007

Résumé: This work deals with the microstructural properties of the Fe–30Co alloy prepared by ball milling of elemental iron and cobalt powders. The obtained mixed powder has been characterized by means of scanning electron microscope, X-ray microanalysis, laser diffraction, X-ray diffraction and microhardness measurements. X-ray line profile analysis based on the Rietveld method and adopting two different models has been used for the microstructural study. The refinement of the X-ray patterns shows that after 3 h of high energy milling the Fe(Co) is formed. The obtained Fe(Co) solid solution is characterized by body centered cubic structure with a lattice parameter a = 0.28564 ± 0.00004 nm and an ellipsoidal crystallite and microstrain field. The dissolution of cobalt in iron matrix is accompanied by the compression of the crystalline lattice by 0.37%. The progress of milling process produces an increase of the Debye–Waller factor and the dislocation density leading to the hardening of the powder. The variation of microhardness with milling time shows a change in hardening mechanisms.

2012
S. Louidi; F.-Z. Bentayeb; W. Tebib; J.J. Suñol; L. Escoda; A.M. Mercier. (2012), Stacking faults and phase transformations study in ball milled Co100−xCrx (x = 0, 20, 50) alloys. Materials Chemistry and Physicshttp://dx.doi.org/10.1016/j.matchemphys.2011.12.008

Résumé: The structural evolution and the phase transformations occurred during milling process of Co100−xCrx (x = 0, 20, 50) alloys are investigated by X-ray diffraction. Microstructural parameters such as the crystallites size, the microstrains, the stacking faults, the dislocation density and the phase fraction were determined from the Rietveld refinement of the X-ray diffraction patterns. The results show the formation of nanostructured alloys which depend on the initial composition of the mixture. In addition, X-ray diffraction indicates that the ball milling induces the fcc to hcp phase transformation in the first stage of milling and the reverse hcp to fcc phase transformation at the end of milling. On the basis of Warren's model, these allotropic transformations were explained by the presence of dislocations and the accumulation of stacking faults in the hcp and the fcc structures.

S. Louidi; F.Z. Bentayeb; W. Tebib; J.J. Suñol; L. Escoda; A.M. Mercier. (2012), Formation study of nanostructured Cr100−xCox (x=10, 90) alloys. Journal of Alloys and Compoundshttp://dx.doi.org/10.1016/j.jallcom.2011.12.083

Résumé: Cr90Co10 and Cr10Co90 mixtures were mechanically alloyed in order to obtain nanocrystalline alloys. The obtained powders were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The structural parameters such as the lattice parameters, the crystallite size, the microstrains and the defect density of the different phases were deduced from the Rietveld refinement of the XRD patterns using the MAUD program. For the Co-rich mixture the evolution with milling time of the SEM micrographs shows a tendency of particle agglomeration. However, in the case of the Cr-rich mixture, the particles tend to the fragmentation. The Rietveld refinement of XRD patterns of the Cr10Co90 mixture reveals the formation of disordered hcp and fcc Co(Cr) solid solutions. In the case of the Cr90Co10 mixture, only a disordered bcc Cr(Co) solid solution is obtained. The changes in the morphology and the structure of the two mixtures are explained on the basis of the mechanical and structural properties.

2010
S. Louidi; F. Z. Bentayeb; J.J. Suñol; L. Escoda. (2010), Formation study of the ball-milled Cr20Co80 alloy. Journal of Alloys and Compoundshttp://dx.doi.org/10.1016/j.jallcom.2009.12.077

Résumé: The ball milling of blended chromium and cobalt powders was carried out in a planetary mill in order to obtain a nanostructured Cr20Co80 alloy. The structural modifications at different stages of the ball milling are investigated with X-ray diffraction. Several microstructure parameters such as the crystallite size, microstrains, stacking faults, dislocation density and phase fractions are determined. As the milling proceeded, the chromium peaks disappeared progressively indicating the dissolution of the chromium atoms into the cobalt matrix. Disordered hcp-Co(Cr) and fcc-Co(Cr) solid solutions were formed after 24 h of milling. The hcp solid solution has a lower value of the crystallite size and a higher degree of microstrains and dislocation density than the fcc solid solution. For prolonged milling (48 h), plastic deformations introduce large amounts of stacking faults in the hcp structure leading to the reverse hcp–fcc transformation of the Co(Cr) solid solution. The kinetic parameters n = 0.81 and k = 0.11, obtained using the Johnson–Mehl–Avrami formalism, correspond to diffusion mechanisms through interfaces and dislocations.

S. Louidi; F.Z. Bentayeb; W. Tebib; J.J. Suñol; A.M. Mercier; J.M. Grenèche. (2010), Amorphisation of Cr–10Co mixture by mechanical alloying. Journal of Non-Crystalline Solidshttp://dx.doi.org/10.1016/j.jnoncrysol.2010.01.015

Résumé: Mechanical alloying of blended chromium and cobalt powders is carried out in order to obtain a nanostructured Cr–10Co alloy. The alloy formation is studied by means of scanning electron microscopy with energy-dispersive X-ray analysis, X-ray diffraction and differential scanning calorimetry. The results show that an allotropic transformation of Co from fcc to hcp structure occurs within the first 3 h of milling. After 12 h of milling, nanostructured bcc-Cr(Co) solid solution is obtained. Contamination of the powder by the milling tools and atmosphere for 24 h of milling contributes to the formation of a high degree of structural disorder. In addition to Fe, Cr and Co oxides, Cr(Co) solid solutions with bcc and unusual hcp structures are formed. The differential scanning calorimetry analysis in the temperature range 50–700 °C gives evidence for the presence of both microstrain relaxation and crystallization of the amorphous-like structures. Heating the 24 h-milled powder at 600 °C leads to the formation of bcc-Cr, Fe oxide and tetragonal σ-CrCo phases.

2008
W. Tebib; S. Alleg; R. Bensalem; N. Bensebaa; F. Z. Bentayeb; J. J. Suñol; J. M. Grenèche. (2008), Structural Characterization of Nanostructured Fe-8P Powder Mixture. Journal of Nanoscience and Nanotechnology http://dx.doi.org/10.1166/jnn.2008.056

Résumé: Nanostructured Fe-8P (wt%) powder mixture was prepared by high energy ball milling in a planetary ball mill (Fritsch P7) under argon atmosphere. The morphology of the particles, the phase identification and the alloying evolution process as a function of milling time are studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and 57Fe Mössbauer spectrometry (MS), respectively. Refinement based on Rietveld method of the XRD patterns and the Mössbauer spectra analysis show that the Fe x P (1 < x < 2) and Fe2P phosphide phases are the main product after 3 h of milling (∼10%). From the XRD Rietveld refinement, it is observed that the Fe2P phase disappears completely after 12 h of milling, while the Fe3P nanophase appears after 9 h and remains for larger milling duration. The lattice structure distortion is evidenced by the lattice parameter changes ofthe milled products. A two structure state of the α-Fe(P) solid solution: α-Fe1 and α-Fe2 is confirmed by both the XRD and MS measurements. After milling for 21 h, a mixture of a disordered two phase α-Fe(P) solid solution, Fe3P nanophase and a small amount of a paramagnetic FeP phosphide phase (∼2%) is obtained.

Safia AlSafia Alleg; Fatima Zohra Bentayeb; Rachid Bensalem; Chafia Djebbari; Lotfi Bessais; Jean Marc Greneche. (2008), Effect of the milling conditions on the formation of nanostructured Fe-Co powders. physica status solidi (a)http://dx.doi.org/10.1002/pssa.200824040

Résumé: Nanostructured Fe–12Co (wt%) powders were prepared by mechanical alloying in a planetary ball mill. The milling process was carried out at different milling conditions. The obtained powders were characterized by X-ray diffraction, 57Fe Mössbauer spectrometry and magnetic measurements. The low and high speed ball-milling conditions lead to the formation of a single and two-bcc Fe(Co) structure, respectively, having different crystallite sizes, microstrains hyperfine parameters and magnetic properties. The average hyperfine magnetic field values: 〈B〉1 = 34.8 T and 〈B〉2 = 28.2 T of the two-bcc Fe(Co) structure could be attributed to the nanocrystalline grains and to the grain boundaries, respectively.

2007
F.Z. Bentayeb; S. Alleg; J.M. Grenèche. (2007), Structural and microstructural study of Fe–31Cr–12Co mixture prepared by ball milling. Journal of Alloys and Compoundshttp://dx.doi.org/10.1016/j.jallcom.2006.08.111

Résumé: Nanostructured Fe–31Cr–12Co mixture was prepared by high energy ball milling (BM) of elemental Fe, Cr and Co powders. The obtained powders were characterized by X-rays diffraction (XRD) using Rietveld's method. The BM leads to the allotropic transformation of Co from FCC to HCP form during the first hour of milling and the formation of a disordered Fe(Cr, Co) solid solution (SS) with BCC structure after 12 h of milling. The microstructural analysis using the profile fitting shows the nanostructured character of the obtained powders. The diffraction line broadening of the SS is Miller indices dependent and is a consequence of anisotropy in size and strains.

2005
N. Bensebaa; S. Alleg; F.Z. Bentayeb; L. Bessais; J.M. Grenèche. (2005), Microstructural characterisation of Fe–Cr–P–C powder mixture prepared by ball milling. Journal of Alloys and Compoundshttp://dx.doi.org/10.1016/j.jallcom.2004.06.075

Résumé: In an attempt to prepare amorphous Fe77Cr4P8C11 alloy by mechanical alloying, powder mixtures of Fe, Cr, P and C (activated carbon) with a purity of 99.9% have been ball milled, under argon atmosphere for several periods up to 90 h, in a planetary ball mill (Fritsch P7). The structure and microstructure of the milled powders have been characterised.

F.Z. Bentayeb; S. Alleg; B. Bouzabata; J.M. Grenèche. (2005), Study of alloying mechanisms of ball milled Fe–Cr and Fe–Cr–Co powders. Journal of Magnetism and Magnetic Materialshttp://dx.doi.org/10.1016/j.jmmm.2004.09.108

Résumé: Mechanical alloyed Fe–31Cr and Fe–31Cr–12Co powder mixtures have been investigated using 57Fe Mössbauer spectrometry and X-ray diffraction (XRD). The ball milling of Fe–31Cr and Fe–31Cr–12Co mixtures during 3 h results, respectively, in formation of nanostructured (Fe,Cr) and (Fe,Cr,Co) solid solutions with body-centred cubic (BCC) and two metastable paramagnetic structures: face centred cubic (FCC) and primitive cubic (PC). The corresponding Mössbauer spectra present a single-line component relative to the paramagnetic phases superposed to a sextet attributed to a BCC disordered alloy. The analysis of the hyperfine field distribution in terms of Fe atomic surroundings further prove the reality of atomic alloying after this short time of milling. The progress of the milling procedure leads to a very disordered structure of weakly magnetic solid solution. Different fitting procedures have been used to model the structural and magnetic changes.

2004
H. Moumeni; S. Alleg; C. Djebbari; F. Z. Bentayeb; J. M. Grenèche. (2004), Synthesis and characterisation of nanostructured FeCo alloys. Journal of Materials Sciencehttp://dx.doi.org/10.1023/b:jmsc.0000039262.37788.b7

Résumé: Nanocrystalline Fe(1−x)Co x (x = 0.12, 0.5, 0.6) mixtures have been prepared by mechanical alloying using a planetary ball mill under several milling conditions. The alloying process between the elemental powders and the microstructure changes of the prepared samples have been investigated using X-ray diffraction (XRD) and 57Fe Mössbauer spectrometry. The XRD patterns refinement on the mechanical alloying products according to the Rietveld method (Maud software) reveals the allotropic transformation of Co from fcc to hcp form and the progressive dissolution of Co into the α-Fe lattice as a function of both Co concentration and milling conditions. The grain size values of the obtained powders reaches a nanometer scale of about 10 nm. Mössbauer results show that the beginning of the solid state reaction between Fe and Co elemental powders depends on the milling conditions. After 24 h of milling, the average hyperfine magnetic fields values of Fe88Co12, Fe50Co50 and Fe40Co60 mixtures are consistent with a disordered and an ordered FeCo solid solution, respectively.

2002
F. Z. Bentayeb; S. Alleg; B. Bouzabata; J. M. Greneche. (2002), Mössbauer Study of Mechanically Alloyed Fe57Cr31Co12. physica status solidi (a) http://dx.doi.org/10.1002/1521-396x(200202)189:3<841::aid-pssa841>3.0.co;2-f

Résumé: Nanostructured powders of Fe57Cr31Co12 were prepared by mechanical alloying from elemental Fe, Cr and Co powders, using a planetary ball mill type Fritsch Pulverisette 7. The powders were characterized by X-ray diffraction and 57Fe Mössbauer spectrometry. A detailed analysis of the diffraction patterns reveals a decrease of the crystalline grain size as a function of milling time. For the first hours of milling, Mössbauer spectra are composed of a magnetic contribution and a single line. The paramagnetic component, whose relative area increases with milling time, can be attributed to paramagnetic Cr-rich clusters. The results are compared to those obtained on the same alloy prepared by conventional melting technique.

F.Z. Bentayeb; S. Alleg; B. Bouzabata; J.M. Grenèche. (2002), Structural Study of Fe-Cr-Co Alloys Obtained by Mechanical Alloying. Hyperfine Interactions (C)http://dx.doi.org/10.1002/1521-396x(200202)189:3<841::aid-pssa841>3.0.co;2-f

Résumé: Nanostructured Fe-Cr-Co alloys were prepared by mechanical alloying (MA) of elemental powders in the following proportions: Fe57Cr31Co12, (Fe,Cr)88Co12 and (Fe,Co)69Cr31. 57Fe Mössbauer and X-ray diffraction (XRD) are used to model the atomic scale alloying mechanism which occurs as a function of milling conditions.

2000
F.Z. Bentayeb; B. Bouzabata; S. Alleg. (2000), Mössbauer study of the annealing effect on low‐alloyed steels. Hyperfine Interactionshttp://dx.doi.org/10.1023/a:1012652119925

Résumé: Structural analyses of Fe-Cr and Fe-Cr-Ni low‐alloyed steels before and after annealing at 600○C using Mössbauer spectrometry, X‐ray diffraction and scanning electron microscopy are reported. At the received state, the two steels present a fine bainitic microstructure with equal hardness. From Mössbauer analysis, two iron sites are identified as substitutional by Cr, Mo, Ni atoms and as insertional by carbon in bainitic ferrite. Both sites are locally deformed by residual stresses. The presence of small quantities of retained austenite and ε carbide has been observed. Annealing for one hour at 600○C causes a decrease in hardness for both steels with a decrease of retained austenite. After longer time of annealing, precipitation of (Fe,Ni)23C6 occurs in the Fe-Cr-Ni steel and increases hardness.