Liste des publications
Segmentation of Weld Defects Using Multiphase Level Set by the Piecewise-Smooth Mumford-Shah Model
This paper deals with the problem of the X-ray image segmentation used to detect weld defects for a non-destructive testing task. In this work we have implemented a multiphase method using the Mumford and Shah piecewise smooth model to extract the size and the texture information of defect and its region. Using this model which is more robust to the noise and less sensitive to the position of the initial curve, we have obtained a maximum of information for several regions in the X-ray image (the geometry of weld beads and defects). Our results show that the model developed can do at the same time the image segmentation and restoration. Voir les détails
Mots clés : Level set
Microstructure and mechanical behavior of dissimilar AISI 304L/WC-Cocermet rotary friction welds
In this work, dissimilar rapid Rotary Friction Welding of WC-Co cermet to AISI 304 L austenitic stainless steel hasbeen conducted using different friction times. The microstructural examination showed that the increase infriction time from 4s to 12s increases the grain size in both the heat affected zone and the thermo-mechanicallyaffected zone and enlarges the extent of the fully dynamically recrystallized zone. EDS analysis revealed theexistence of a FeeCreW rich band along the WC-Co/AISI 304 L interface in the central region of the weld jointand its absence from the peripheral region. The formation of this band suggests the occurrence of a mutual inter-diffusion between the cermet and the steel which enhanced the metallurgical bonding of the interface. Themechanical behavior investigated by nano-indentation measurements and nano-scratch tests revealed that, re-gardless the friction time effect and considering the 304 L ASS side, the highest hardness (HIT) and the lowestYoung's modulus (EIT) values were recorded in the fully dynamically recrystallized zone. Besides, the increase offriction time resulted in an increase of hardness and Young's modulus of each zone in the AISI 304 L steel side. Voir les détails
Mots clés : Rotary friction welding, WC-Co cermet, AISI 304L ASS, microstructure, Intre-diffusion, Bonding strength
Comparative investigation of the Ni and the Fe effect on the structure andmechanical response of a WC-W-Ni hardmetal obtained by infiltration
In the present work, and in order to enhance the efficiency of drilling tools for the oil and gas industry, theinfluence and performance of Ni and Fe during spontaneous infiltration on a WC-W-Ni composite materialmechanical behaviour was addressed. Solid-state activity of Fe and Ni during infiltration exhibits partial dissolution in the metallic binder. The chemical affinity between Fe and Ni, provided by the Fe powder and thebinder respectively, derived on the formation of the (Fe, Ni) solid solution and FeNi3 intermetallic precipitates inthe particle/matrix diffusion region, with a hardness (12 GPa) close to that of WC and high elastic modulus (230 GPa). Furthermore, the diffusion of Fe to the matrix leads to the formation of sub-micrometer precipitatesof α-Fe with some (Ni, Mn) in solid solution and of Ni3Sn with a small amount of Cu dissolved, driving to anincrease of about 30% in its elastic modulus, and without appreciable effect in the hardness observed. Voir les détails
Mots clés : Metal matrix composites, Liquid-solid reactions, Precipitation, powder metallurgy, diffusion, mechanical properties
Microstructure and mechanical behavior of dissimilar AISI 304L/WC-Co cermet rotary friction welds
In this work, dissimilar rapid Rotary Friction Welding of WC-Co cermet to AISI 304L austenitic stainless steel has been conducted using different friction times. The microstructural examination showed that the increase in friction time from 4s to 12s increases the grain size inboth the heat affected zone and the thermo-mechanically affected zone and enlarges the extent of the fully dynamically recrystallized zone. EDS analysis revealed the existence of a Fe-Cr-W rich band along the WC-Co/AISI 304L interface in the central region of the weld joint and its absence from the peripheral region. The formation of this band suggests the occurrence of amutual inter-diffusion between the cermet and the steel which enhanced the metallurgical bonding of the interface. The mechanical behavior investigated by nano-indentation measurements and nano-scratch tests revealed that, regardless the friction time effect and considering the 304 L ASS side, the highest hardness (HIT) and the lowest Young’s modulus (EIT) values were recorded in the fully dynamically recrystallized zone. Besides, the increase of friction time resulted in an increase of hardness and Young’s modulus of each zone in the AISI 304L steel side. Voir les détails
Mots clés : Rotary friction welding, WC-Co cermet, AISI 304L ASS, microstructure, Intre-diffusion, Bonding strength.
Nitriding effect on structural stability and magnetic properties of FeAl alloys:DFT study
Using the DFT calculations, the phase stability, structural deformation and magnetic momentof Fe-riche FeAl alloys in presence of different percents of nitrogen were calculated. Theformation enthalpy of these Fe-Al alloys indicates that N preferred the octahedral site than thesubstitution one. Significant changes occur in this energy, affected by N and Fe contentcausing local distortions. From 25 at.% N, the phenomenon of saturation appeared and thesubstitution takes place. The addition of 6 at.% N stabilizes Fe 9 Al 7 and Fe 10 Al 6 . The presenceof N atom leading to decrease the total magnetic moment of FeAl nitride when the magneticorder is antiferromagnetic between N and Fe atom. This magnetic moment increased by theferromagnetic coupling between Fe and N, thus increasing the Fe local magnetic moment andthe magneto-volume effect. Voir les détails
Mots clés : Nitriding, Magnetic Properties, Structural Stability., FeAl Alloys, DFT
Structural, Electronic and Mechanical Properties of C14-Mg 2 RE(RE=Eu, Er, Tm, Yb and Lu) Laves Phases: A DFT Study
The Pseudo-Potential Density Functional Theory (PP-DFT) method is applied to investigatethe structural, electronic and mechanical properties of C14-Mg 2 RE Laves phases, with RE being Eu,Er, Tm, Yb and Lu. The predicted cell parameter and c/a ratio of each compound are in good agreement with experimental and theoretical results. Moreover, the studied alloys exhibit a metalliccharacter, which is attributed to the presence of Mg atoms in the C14 Laves phase. Also, theformation of C14-Mg 2 RE is found to be controlled by the hybridisation between Mg p states and RE-d and f states. From a mechanical property analysis, the studied alloys are found to be mechanicallystable. The Mg 2 Lu compound exhibits higher ductility, while Mg 2 Er exhibits the smallest one.Finally, Mg 2 Yb is found to be more anisotropic than other phases. Voir les détails
Mots clés : A DFT calculations, B Magnesium based Laves phases, C Density Functional Theory (DFT), D Mechanical properties, E Electronic properties
Effect of solution treatment on the microstructure, micromechanical properties, and kinetic parameters of the β → α phase transformation during continuous cooling of Ti-6Al-4V titanium alloy
The aim of this study is to examine the effect of solution treatment temperature (STT) on the microstructure, the micromechanical properties, and the kinetic parameters of the β → α phase transformation during continuous cooling of the dual phase titanium alloy Ti-6Al-4V. Increasing the STT from 1050 °C to 1200 °C delays the formation of the α phase during cooling and increases the value of its activation energy. The microstructural analysis reveals the emergence of αW platelets from protuberances on the αGB / αW interface. The investigation of the morphology of the αW platelets reveals the presence of ledges on their longest side showing a sharp extremity. The micromechanical properties determined by nanoindentation and microhardness tests are almost insensitive to the cooling rate but are strongly affected by the STT; the higher the STT, the lower the overall microhardness of the Ti-6Al-4V alloy. In addition, the STT affects the microhardness and the Young’s modulus of both α and β phases differently; when the STT increases, the microhardness and the Young’s modulus of the α phase decrease whereas those of the β phase increase. Voir les détails
Mots clés : Ti-6Al-4V, solution treatment, ledge mechanism, interface instability, Nanoindentation, partitioning
Isothermal and non-isothermal precipitation kinetics in Al–Mg–Si-(Ag) alloy
In the present work, isothermal and non-isothermal precipitation kinetics in a 6063 aluminium alloy containing a small silver (Ag) addition have been investigated using Vickers microhardness and Differential Scanning Calorimetry (DSC) measurements respectively. Isothermal kinetics analysis showed that β'' phase precipitation obeyed the Johnson-Mehl-Avrami (JMA) model. The DSC analysis revealed that Ag addition modified the precipitation sequence in the investigated 6063 aluminium alloy through the formation of an additional metastable pre-β'' phase. An approach based on the additivity concept has been applied to the heating DSC diagrams to investigate the β'' phase precipitation. The obtained Avrami exponent values from this approach led to suggest that the β'' phase precipitation proceeded through two processes during continuous heating. The Avrami exponent value obtained at the final stage of the transformation was consistent with that obtained from the isothermal analysis, whereas the corresponding activation energy was higher than the one calculated from the isothermal analysis and Kissinger's method. It was also established that the precipitation kinetics of the β'' phase was enhanced by the formation of the precursor phase pre-β''. Voir les détails
Mots clés : 6063 aluminium alloy, Ag addition, Precipitation kinetics, JMA model, Additivity concept
Natural extract of Opuntia ficus indica as green inhibitor for corrosion ofXC52 steel in 1M H3PO4
The purpose of this study is to evaluate the anti-corrosive effect of natural extract of Opuntia Ficus Indica (O.F.I) for XC52steel in 1M H3PO4. Experimental work has been achieved by weight loss, potentiodynamic polarization and EISmeasurement, as well as SEM surface characterization. Among the results obtained, we can mention an inhibitory efficiencyof 90% by gravimetric method and 83.9% by electrochemical method at 10% (v/v) of O.F.I. Moreover, The O.F.I extract actsas a mixed inhibitor; however, adsorption free enthalpy indicates a physisorption. The adsorption obeys the Langmuirisotherm model. These results have been improved by SEM micrographs Voir les détails
Mots clés : corrosion, Opuntia ficus indica, EIS, green inhibitor, XC52 steel
Endurance and Damage in Fatigue of Symmetrical Configuration 2P-2V-2P Perlon-Glass-Acrylic Composite Laminates of Orthopaedic Use
In this paper, an experimental characterization of fatigue behaviour on prismatic specimens of a symmetrical laminated composite material perlon- glass- acrylique 2P-2V-2P for orthopaedic use is conducted. Cyclic repeated solicitation is employed corresponding to applied minimum stress σmin equal zero. The various loading levels imposed on the specimens are 80%, 70%, 60%, 55%, 45%, 35% and 25% of the value of the static failure strength measured in flexure. A significant scatter characterizes the results of material fatigue lifetime. That is the consequence of the heterogeneity of the material structure. The scattered phenomenon prevents any prediction of the lifetime with a good probability using Wohler equation. This enables defining a constant degradation rate by 10% cycle decade. The microstructure morphology study through microscopic observations is also discussed and analyzed. The damage state in fatigue is characterized by a combination of density and orientation of micro-cracks. This damage is mainly due to mechanisms complexity of matrix micro-cracking, inter facial exfoliation, debonding and delamination. The damage evolution stages in the case of cyclic loading have the same nature than those found in static loading but have different chronology and scale Voir les détails
Mots clés : perlon, acrylic, Orthopaedic, fatigue, Scatter