Métallurgie
Assemblage des Alliages Légers (Aluminium, Magnésium) par Faisceau de Haute Energie (TIG & Laser).
Le soudage des alliages légers aluminium et magnésium est un domaine de recherche en cours d’exploration de par la demande de plus en plus accrue d’allègement des structures dans les domaines aéronautique et automobile. Leur propriété physique de conductibilité thermique et chimique de formation d'oxyde, compliquent leur soudabilité opératoire dans un premier lieu et la soudabilité métallurgique de transformation de phases et de structures dans un second. C’est dans un contexte de compréhension et de maitrise technologique des procédés de soudage TIG et Laser Yb:YAG, que ce travail est initié et évaluer le comportement métallurgique et mécanique des jonctions. Pour cela, un protocole d'essais est élaboré pour s'assurer de la soudabilité opératoire mais aussi l'utilisation de techniques d'acquisition thermiques par implantation de thermocouples et par thermographie infrarouge, sont appliquées. Les caractérisations métallurgiques par diffraction des électrons radiodiffusésEBSD et Diffraction des rayons X (DRX) en plus de la microscopie optique et électroniques sont utilisées. Le comportement mécanique est évalué par des essais de dureté Vickers et de traction et par corrélation d’images Voir les détails
Mots clés : Procédé TIG, Procédé Laser Yb :YAG, Alliage de magnésium, Diffraction des électrons radiodiffusés EBSD, propriétés mécaniques
Investigation ?n Dry Sliding Wear Performance and Corrosion Resistance of 13Cr5Ni2Mo Supermartensitic Stainless Steel
This work aimed to study the microstructure, wear and corrosion resistance of supermartensitic stainless steel (SMSS). Heat treatment applied to samples consists of quenching after austenitization at elevated temperature (1250 °C) followed by a double tempering at 650 °C. Conventional mechanical properties, scanning electron microscopy (SEM/EDS) analysis and X-ray diffraction methods (XRD) are used to analyze the microstructure and to evaluate the wear mechanisms. The potentiodynamic polarisation and the electrochemical impedance spectroscoopy (EIS) methods are used to evaluate the corrosion resistance in both the 0.5M H2SO4 and 0.5M NaCl aggressive media. The microstructure is mainly composed with tempered lath martensite, small quantity of retained austenite and carbides. Oxidative and abrasive wear dominated the wear process in dry condition. During the corrosion process, the same mechanism of degradation was found in both the 0.5M NaCl and 0.5M H2SO4. Voir les détails
Mots clés : Supermartensitic steel, microstructure, friction, Wear Corrosion
Plastic Deformation Effect on Wear and Corrosion resistance of Super Martensitic Stainless Steel
The microstructure and the mechanical properties of a super martensitic stainless steel (SMSS) were investigated in this study. Test specimens were taken from seamless tube generally used in oil and gas industries. The specimens were plasti- cally deformed by tension from its as-received state to different levels of elongation at 2%, 10%, and 15%, respectively. The focus was to study the influence of plastic deformation on the tribological behavior against alumina balls in dry conditions and the corrosion resistance in 3.5% NaCl solution. Analysis results showed an abrasive wear as the main wear mechanism. Plastic deformation prior to sliding wear test increases wear resistance as the deformation rate increases. Based on the elec- trochemical experiments, all of the specimens showed an increase in their corrosion resistance i.e., the corrosion potential Ecorr (vs. Ag/AgCl) tends to move toward more noble values with respect to the initial potential. The greatest polarization resistance was displayed by the specimen with 10% of deformation rate. Voir les détails
Mots clés : Super Martensitic Stainless Steel, Cold deformation, wear, corrosion
On the evolution of microstructure, texture and corrosion behavior of ahot-rolled and annealed AZ31 alloy
The microstructure and texture evolution of an AZ31 alloy were investigated after hot rolling and subsequentannealing using electron backscatter diffraction (EBSD). First, the alloy was hot-rolled at 350 ? C up to low,medium and high strain (20, 50 and 85% of thickness reduction, respectively). The alloy samples where thenannealed at 350 ? C for 2, 10 and 60 min. The effect of strain level and annealing on corrosion behavior inseawater was also evaluated using electrochemical tests. At low strain, the microstructure was characterised bythe absence of twinning, mainly due to the prior thermo-mechanical history of the as-received alloy. However,various modes of twinning were observed at medium strain. At high strain, the dynamic recrystallization processresulted in a microstructure with a typical basal texture. The results demonstrate that twins are responsible forthe deviation of {0002} basal poles from normal towards the transversal direction. Annealing at 350 ? C for up to60 min led to normal grain growth in all the samples. In medium and highly strained samples, the deformationtexture was retained, while the low strain sample underwent noticeable changes due to the absence of dynamicrecrystallization. A synergetic effect of grain refinement and texture weakening was responsible for the alloy’senhanced corrosion resistance.AZ31 alloyCorrosionDynamic recrystallizationStatic recrystallizationRolling Voir les détails
Mots clés : AZ31 alloy, corrosion, Dynamic recrystallization, Static recrystallisation, rolling
Study of The Structure and Corrosion Behavior of Al-15%MoAlloy
The influence of the addition of molybdenum on the structure and corrosion behaviour of aluminium was studied using optical microscopy, scanning electron microscope (SEM),potentiodynamic polarization and electrochemical impedance spectroscopy. The results showthat the addition of 15%wt molybdenum causes the precipitation of the Al12Mo intermetallic phase which appears in plate form on the αAl matrix. The results of the electrochemical tests show that the addition of molybdenum displaces the corrosion potential of aluminium towards positive values from -699 mV/ECS to -633 mV/ECS and increases the charge transfer resistance from to 4752 Ω.cm2 to 6608 Ω.cm2. Voir les détails
Mots clés : corrosion, Al-15%MoAlloy, Electrochemical behavior
Tribological behavior and microstructural characterization ofaustenitic stainless steel stabilized with Nb and V
This study deals with the influence of the addition of vanadium and niobium with concentrations of 1.2% and 0.14%, respectively, on the variation of the microstructure, and the tribological behavior of an AISI309 austenitic stainless steel. The studied specimens were structurally characterized by optical microscopy, scanning electron microscopy (SEM) X-ray diffraction and differential scanning calorimetry (DSC). These samples were also subjected to a tribological study using the friction wear test. The results show that the addition of vanadium and niobium causes precipitation of stable carbides (VC, NbC) which in turn causes a decrease of the chromium carbide precipitation rate. Tribological test results have also shown that the addition of these two elements improves the wear resistance of AISI309 austenitic stainless steel by decreasing the coefficient of friction from 0.824 to 0.554. Voir les détails
Mots clés : Vanadium, niobium, tribological, wear, friction, AISI309
Heat Treatment Effect on the Microstructural, Hardness and TribologicalBehavior of A105 Medium Carbon Steel
The present work is a contribution in investigating the effect of heat treatment on microstructure, hardness, and friction wear of A105N steel. Samples of 25x25 mm² cross-section and15mm thickness have been prepared from the as-received material and then heat-treated. The samples were austenitized at 1050°C for 60 minutes followed by water quenching, then tempered at 500 and700°C for 120 minutes. Microstructural changes and their effect on the wear resistance and hardness were investigated according to the applied heat treatments. The main results show that after quenching the structure is mostly composed of quenched martensite, which confers high hardness and friction resistance to the steel. While the tempered structure is composed of tempered martensite and ferrite.As the temperature rises to 700°C, the tempered martensite decreases and is fully transformed to ferrite and cementite. A good wear resistance is expressed by a low friction coefficient and a low wear rate is achieved by tempering at 500°C. Voir les détails
Mots clés : tempering, Quenching, friction, A105, hardness, heat treatment, wear
Investigation оn Dry Sliding Wear Performance and Corrosion Resistance of 13Cr5Ni2Mo Supermartensitic Stainless Steel
This work aimed to study the microstructure, wear and corrosion resistance of supermartensitic stainless steel (SMSS). Heat treatment applied to samples consists of quenching after austenitization at elevated temperature (1250 °C) followed by a double tempering at 650 °C. Conventional mechanical properties, scanning electron microscopy (SEM/EDS) analysis and X-ray diffraction methods (XRD) are used to analyze the microstructure and to evaluate the wear mechanisms. The potentiodynamic polarisation and the electrochemical impedance spectroscoopy (EIS) methods are used to evaluate the corrosion resistance in both the 0.5M H2SO4 and 0.5M NaCl aggressive media. The microstructure is mainly composed with tempered lath martensite, small quantity of retained austenite and carbides. Oxidative and abrasive wear dominated the wear process in dry condition. During the corrosion process, the same mechanism of degradation was found in both the 0.5M NaCl and 0.5M H2SO4. Voir les détails
Mots clés : Supermartensitic steel, microstructure, friction, wear, corrosion
Élaboration par pulvérisation cathodique magnétron de couches minces en vue de leur utilisation comme biomatériaux. Caractérisation à l’usure et à la corrosion
The design and development of biomaterials with multifunctional surfaces by magnetron sputtering is the final objective of this work. Different mechanical and structural properties of the films obtained in monolayers (ZrN and Ta) and in multilayers (Ta / ZrN) were determined and analyzed. Investigative tools were X-ray diffraction (DRX), optical microscopy (OM) and scanning electron microscopy (MEB) and atomic force microscopy (AFM).Mechanical properties such as nanoindentation, stress measurements and adhesion tests were also carried out. The tribological and electrochemical performances of the different coatings were analyzed and compared. The Ar / N2 + O2 ratio in the plasma shows a negative influence of the O2 on the performances in wear and corrosion of ZrN Less oxygen leads to better results. The results obtained on multilayer ZrN/Ta coatings with different thicknesses show that they have intermediate properties to those of the monolayers that constitute them. Mechanical and tribological properties, low coefficient of friction of the Ta layer and good wear resistance of the ZrN layer. The M2 multilayer coating (ZrN/Ta) having the thickness of the layers which decreases with the increase in the number of periods has the best mechanical characteristics highlighted by scratch test and nanoindentation. Voir les détails
Mots clés : Biomaterials, PVD, tribology, corrosion
Dry sliding wear performance of an annealed TiNi alloy with differentnickel contents
The wear behaviour of the TiNi alloy tested at different conditions (2 and 4Nas applied loads and 40,50 an 60 wt%as nickel contents) was investigated. For this purpose, two main experimentaltechniques consisting of wear and indentation tests were used. Scanning electron microscopy (SEM)and laser source profilometry were employed to reveal the wear mechanisms and the affected wornsurfaces. Furthermore, design of experiments planning introducing factorial design as well as responsesurface was adopted to attempt predicting the coefficient friction according to the planned testparameters. Nanoindentation results showed that all the TiNi alloys are harder than a TA6V4 alloywhich is commonly used in dental implant. Particularly, the TiNi60 alloy exhibited superiorsuperelasticity, characterized by a lower E/Hratio and a higher depth recovery ratio than the TA6V4alloy. Besides, the wear rates underwent a substantial increase with the increase of the applied load buta decrease with increasing the Ni content. The worn surfaces analyses revealed an enhanced resistanceto adhesive and abrasive wear with increasing nickel content. Voir les détails
Mots clés : TiNi alloy, factorial design, Wear Resistance, superplastic behaviour