Liste des publications
Effet du niobium sur la résistance à l’usure d’une fonte au chrome traitée thermiquement
RésuméLes fontes au chrome sont bien connues pour leurs propriétés à l’usure. Elles sont utilisées dans les domaines miniers, cimentiers ainsi que tant d’autres. Leurs facultés de résister à l’usure sont principalement dues à leur microstructure qui est constituée d’un réseau de carbure eutectique du type M7C3 contenu dans une matrice austénitique ou martensitique. Plusieurs chercheurs ont exploré la possibilité d’améliorer les propriétés à l’usure de ces fontes en agissant sur la microstructure, la morphologie des composants microstructuraux ainsi que sur leur distribution. Le présent travail consiste à étudier l’effet du niobium sur le comportement à l’usure d’une fonte au chrome. Des caractérisations par microscopie optique, usure par abrasion et par frottement sont réalisées dans le but de déterminer la résistance à l’usure de cette fonte et le type de microstructure ayant été à l’origine de cette amélioration. Les résultats obtenus montrent que la fonte étudiée est une fonte à 15 % de chrome. L’addition du niobium a eu un effet sur la microstructure ainsi que sur les résistances par abrasion et par frottement des échantillons de fontes traitées. La résistance à l’usure augmente avec l’accroissement de la teneur en niobium. Voir les détails
Mots clés : Fontes au chrome, usure, carbures eutectiques, éléments d’alliages
Combined use of principal component analysis and self organization map for condition monitoring in pickling process
Process monitoring using multivariate statistical process control (MSPC) has attracted large industries types due to its practical importance and application. In this paper, a combined use of principal component analysis (PCA) and self organization map (SOM) algorithms are considered. Habitually PCA method uses T2 Hoteling's and squared predicted error (SPE) as indexes to classify processes variability. In this paper, new version of indexes called metric distances obtained from the self organization map (SOM) algorithm replace the conventional indexes proper to PCA. A comparative study between SOM, the conventional PCA and the hybrid form of PCA–SOM is examined. Application is made on the real data obtained from a pickling process. As shown in different figures, the combined approach remains important comparatively to PCA but not more than SOM. Voir les détails
Mots clés : component analysis, Condition monitoring
CARACTÉRISATION DES ASSEMBLAGES SOUDÉS PAR LEPROCÉDÉ DE SOUDAGE TIG DES ALLIAGESD’ALUMINIUM 7075 T6
Notre travail consistait à étudier l’influence des traitements thermiques surla dureté de l’alliage d’aluminium 7075 T6 et de mieux distinguer lescaractéristiques de l'évolution de la structure lors du procédé de soudage TIG dansla zone affectée thermiquement. On a remarqué que les évolutions de la solutionsolide sursaturée aux cours des traitements de vieillessement sont conformes auxséquences des précipitations classiques. Une augmentation ou un prolongement à un maintien isotherme, conduit à une apparition de phases d’équilibres incohérentes avec la matrice. L’expérience a permis de mettre en évidence l’évolution de l’état deprécipitation à travers la soudure. Voir les détails
Mots clés : Procédé de soudage TIG, alliages d’aluminium 7075 T6, traitements thermiques, propriétés mécaniques et m icrostructures
Ultrasonic Inspection of Composite Materials Using Minimum Entropy Deconvolution
In this work, the Minimum Entropy Deconvolution (MED) method, developed for ultrasonic signals, is used to address the problem of delamination defect detection in Composite Materials. Standard deconvolution techniques suppose that the wavelet is minimum phase but generally make no assumptions about the amplitude distribution of the primary reflection coefficient sequence. For a white reflection sequence the assumption of a Gaussian distribution means that recovery of the true phase of the wavelet is impossible; however, a non-Gaussian distribution in theory allows recovery of the phase. It is generally recognized that primary reflection coefficients typically have a non-Gaussian amplitude distribution. The minimum entropy deconvolution (MED) method supposes whiteness but seek to exploit the non-Gaussianity. This method do not assume minimum phase. The deconvolution filter is defined by the maximization of a function called the objective. The algorithm is tested on simulated data and also tested on real ultrasonic data from multilayered composite materials. Voir les détails
Mots clés : blind deconvolution, composite, Nondestructive Testing (NDT), Ultrasonic
The Effect of Solar Spectral Irradiance and Temperature on the Electrical Characteristics of a ZnO-SiO2-Si(N) Photovoltaic Structure
The aim of this article is to present an analytic study of the impact of changing solar spectrum and temperature on the performance and electrical characteristics of a MIS solar cell. With this intention, one simulation of the spectral response and the current-voltage characteristic was carried out using a simulation program designed under ‘Visual Basic 5’ language for this reason. Our study is made on a ZnO-SiO2-Si (N) solar cell; it proves that the spectral response has higher collection efficiency for carriers generated by ultraviolet light and a conversion efficiency of about 18 % can be obtained under AM1 solar spectrum and at ambient temperature. The results presented indicate also that the increase in solar cell’s temperature results a degradation of their performances. Voir les détails
Mots clés : MIS solar cell, Solar spectrum, Spectral response, I (V) characteristics, Temperature
Solid state amorphization transformation in the mechanically alloyedFe27.9Nb2.2B69.9 powders
Mössbauer spectrometry and Rietveld analysis of X-ray diffraction patterns were used to follow the solid state amorphization transformation during the milling process of the Fe27.9 Nb2.2 B69.9 powders. The reaction between elemental Fe, Nb and B powders leads to the formation of the Nb(B) and Fe(B) solid solutions after 1 and 10 h of milling, respectively. A mixture of -Fe, Nb(B) and highly disordered Fe(Nb, B) solid solution is found after 25 h of milling. An amorphous structure is obtained on further milling time (100 h). From the Mössbauer spectrometry results, it is observed that the total mixing of the elemental powders, at the atomic level, is achieved after 50 h of milling and a stationary state corresponding to a full paramagnetic amorphous phase is reached after 100 h of milling. The amorphization process can be described by an Avrami parameter close to n = 1. Voir les détails
Mots clés : Nanostructures Powder metallurgy X-ray diffraction Mössbauer effect
SOLID STATE AMORPHISATION OF A Fe-Co-Nb-B POWDER MIXTURE BY MECHANICAL ALLOYING
L'alliage Fe61Co21Nb3B15 a été préparé à partir d'un mélange de poudres par broyage mécanique haute énergie. Les changements structuraux et microstructuraux ont été suivis par diffraction des rayons X (DRX), spectrométrie Môssbauer, et calorimétrie différentielle programmée (DSC). Une structure amorphe, hautement désordonnée dans laquelle sont logés des grains de taille nanométrique de borure de fer, a été décelée, après un broyage de 48 h, par DRX et par spectrométrie Môssbauer. Un processus de recristallisation mécanique mène à la formation de nano-grains de α-Fe et α-FeCo, après un temps de broyage prolongé. Le désordre dans les poudres broyées a été confirmé par DSC où plusieurs courbes exothermiques se chevauchent sur un large domaine de température. Ce comportement provient de la relaxation des contraintes et du grossissement des grains. Voir les détails
Mots clés : Recristallisation ; Poudremétallique ; Etatamorphe ; Microstructure ; Amorphisation ;Alliage base fer ;Alliage mécanique ;Métallurgie poudre ; Broyage ;
Plasma diagnostics in gas metal arc welding by optical emission spectroscopy
The plasma column in a metal inert gas welding process is investigated by optical emission spectroscopy and high-speed imaging. The concentration and repartition of iron vapours are measured and correlated with the plasma and electrode geometric configuration. Plasma temperatures and electron densities are also measured for each studied position in the plasma. The temperatures are calculated using two different methods, allowing validation of the local thermodynamic equilibrium state of the plasma. The results show a maximum temperature of 12500K in the upper part of the arc, away from the arc axis. The iron concentration reaches a maximum of 0.3% close to the anode and strongly decreases along both the vertical and radial directions.The plasma thermophysical properties, calculated from this plasma composition, are then discussed regarding the metal transfer mode. Voir les détails
Mots clés : GMAW, Optical Emission Spectroscopy, Boltzmann Plot, Sola method, LTE
Anode carbon enrichment in GMAW
The shielding gas used in the welding process has a strong influence on the metal transfer characteristics. When the gas is chemically active the physicochemical properties of the electrodes can be strongly altered which can increase or decrease arc stability. In order to get a better control over the process it is essential to understand how the electrodes are affected. As the electrode extremities are molten they can easily adsorb gases from the shielding gas, which can affect their microstructure. CO2 is one of the most commonly used active shielding gases. It is then interesting to know if the liquid metal at the extremity of the electrode can adsorbed the carbon it supplies, as it has strong influence on steel mechanical properties. Besides, various phases can form during metal cooling, depending on its concentration. It is then possible to get information on the carbon content by studying the ratio between phases. In order to show a possible enrichment, only the relative spatial evolution can be studied and no accurate phase identification is needed. Cross sections of the samples have been studied, using mainly optic microscopy. The two main phase ratio have been calculated after processing the obtained images. The results show a higher ratio of the phase associated to the highest carbon content close to the sample periphery, which support the hypothesis of carbon adsorption by the molten metal. Voir les détails
Mots clés : welding, microstructure, CO2, carbon, anode, Ferrite
Contribution to crystallographic slip assessment by means of topographic measurements achieved with atomic force microscopy
In this paper, atomic force microscopy (AFM) is used to quantitatively characterize the plastic glide occurring during tensile deformation of a duplex 2205 stainless steel sample. We demonstrate that an appropriate treatment of the topographic image issued from AFM measurements allows precise and quantitative information about the characteristics of plastic deformation and especially the amount of crystallographic slip. Voir les détails
Mots clés : AFM, Crystallographic slip, Plastic deformation, Duplex steel