Sciences des matériaux
Experimental study of shot peening effect onthe surface of austenitic stainless steels :roughness, residual stresses and workhardening
Shot peening is a mechanical surfacetreatment widely used in automotive and aerospaceindustries to enhance the fatigue life of mechanicalparts. In this process, many small and hard particles,called shots, are projected at high velocities on to thesample. The multiple impacts plastically deform thematerial surface and induce an in-plane compressiveresidual stress field near the surface. Roughness,compressive residual stress and work hardening of anAISI 304 austenitic stainless steel was studied toexplain it evolution according to the Almen intensityand mechanical properties. Shot peening increasessurface hardness levels. We can confirm in case ofCSP the highest microhardness observed at topmostsurface. According to these results it can beconsidered, that after CSP application, themicrohardness in depth of 0.025 mm increased fromabout 220 HV to 350 HV. Voir les détails
Mots clés : -shot peening, residual stresses, work hardening, Almen intensity, roughness, FWHM.
Study of nickel silicide by X- ray diffraction
In order to understand fully the results from X-ray diffraction oscattering analysis, it is benefecial to understand the interactionsbetween X-rays and matter. X-ray methods are generally nondestructive, in that sample preparation is not required, and they canprovide a very appropriate route to obtain structural information onthin films and multilayers. Analysis can be performed across thewhole spectrum of material types from perfect single crystals toamorphous materials.In this work, X-ray diffraction was involved to study the formationof crystalline nickel silicide phases. For this purpose, Ni nanometricthin films were deposited on Si (100). XRD technique have shownthat the NiSi silicide is the predominant phase at 350°C. For theannealed samples at 500°C, only NiSi monosilicide is detectedWhen the annealing temperature increases to 750°C the NiSi2disilicide is the main formed phase. The obtained samples wereanalyzed using scanning electron microscopy (SEM), it show asurface morphology depending strongly on the substrateorientation. Voir les détails
Mots clés : thin film, nickel silicides, X-ray, XRD
Effect of roller burnishing parameters on roughnesssurface and hardness of steel S355J0 specimens byusing response surface methodology
Burnishing is a cold working process with superficialplastic deformation, which is to exert an external pressurethrough a very hard and smooth roller or ball on a surface tooccurs a uniform and work-hardened surface, makes it possibleto reduce roughness, to increase the hardness and to produceresidual stresses of compression The steel S 355 J0 specimenswere machined on a conventional lathe to the proper dimensions,these machined specimens were then burnished by a simplelocally designed and fabricated roller-burnishing tool. The mainobjective in this work is to determine a mathematical modelsstatistically based on experimental design (response surfacemethodology) using central composite second-order rotatabledesign which allows to give the relationship between the two outparameters surface roughness and hardness representative of thesuperficial layer surface caused by the four internal rollerburnishingparametersnamely:burnishingspeed,force,feedandnumberof passes of the tool. The experimental results indicatethat feed, burnishing force and speed are the most important andsignificant parameters to improve roughness surface and feed,speed, burnishing force and number of passes are the mostimportant and significant parameters to improve superficialhardness of steel S 355 J0 specimens. The surface roughness andhardness were improved to 0.15µm from about 2.5µm and to 226Hv from 176 Hv respectively. Voir les détails
Mots clés : roller-burnishing, steel S355J0, surface roughness, superficial hardness, response surface methodology
Influence of sintering temperature on thedensification of copper matrix composite reinforcedwith CoAl particle developed by SHS
This work focuses on the influence of the sinteringtemperature of a copper matrix composite and CoAl particlesproduced by SHS (Self Propagating High temperatureSynthesis).In a first step, Co-50at.%Al mixture is sintered at 950°C to obtainthe CoAl compound that will be milled for 24 hours and sinteredin presence of copper in order to a preparation of a metal matrixcomposite. Then, the CoAl-50wt. %Cu mixtures are compressedunder a pressure of 350MPa and sintered at two differenttemperatures (solid and liquid phase) under argon.The SEM examination of the composite sintered in solid phaseshows the ramifications of copper in CoAl particles, whichhighlights a diffusion of Cu through the nano pores particles.Some particles present a phase contrast, which reveals theinhomogeneity of diffusion. The EDS-X analysis confirms thisresult since we find an important quantity of copper inside aparticle. The Cobalt and aluminum are also found in the matrix.Moreover, the discontinuity is observed with the interface CoAlCu. It seems that liquid sintering phase would leads to ahomogeneous diffusion, better wetting of particles and higherdensification. A sphering of CoAl particles is also observed in thecase of the composite sintered in liquid phase, which reflects thephenomenon of dissolution-precipitation at the edges of CoAlparticles.To a complementary results, X-ray diffraction analysis (XRD)was also performed. The diffractogram of CoAl-Cu compositesintered in liquid phase reveals the presence of Cu and CoAl withshift of the Cu peaks to the left, reflecting an increase in theparameter. This swelling of the mesh of copper is due to thesubstitution of copper atoms by those of aluminum and cobalt.After the calculation of the open porosity in the compositessintered in liquid and solid phase, we found a better densificationof the composite sintered in liquid phase with a rate porosity of2%. Voir les détails
Mots clés : composite materials, intermetallics, SHS, SEMEDS X, XRD
Behaviour of dislocations near phaseboundaries in the anisotropiclinear elasticity theory
The image force undergone by amatrix dislocations close and parallel to aninterphase boundary is studied in Ag-X bicrystalswith X : Pb, Cu and Ni for disorientations rangingbetween 0° and 90°. The elastic energy of dislocationboundaryinteraction is calculated within theframework of anisotropic linear elasticity. It isrelated to the difference of the two metals shearmoduli. It is about a few hundred pico Joule permeter. The image force can be repulsive or attractiveaccording to the sign and the intensity of shearmoduli difference. The isoenergy maps have varioussymmetries according to the disorientation. Voir les détails
Mots clés : nterphase Boundary, Dislocation, Elastic Interaction, Image Force, Anisotropic elasticity, CFC Structure.
Study Ni70al20Si10prepared by mechanical alloying
Alloys based on nickel, aluminum and siliconhave been extensively studied because they are of great interestfor high temperature structural applications (low density, highspecific strength, greater resistance to oxidation, hightemperature resistance). The properties of these materials can beimproved by mechanical alloying. In this work we havedeveloped and studied intermetallic Ni70al20Siprepared bymechanical alloying. The powder mixtures were crushed in aplanetary ball mills for synthesizes shades off balance, the millingtime was a factor in the study of structural changes of thiscompound to 50 hours of milling. Characterizations by SEM andXRD are used to derive the properties of this compound. Voir les détails
Mots clés : intermetallic alloy, Mechanical Alloying, Aluminum- Nickel-Silicon, SEM, XRD
Effects of the stacking fault on free surfaceFePt L10
Chemical ordered FePt L10, which is characterizedby a tetragonal distortion of a few percent along the c-axis,accompanied by an alternating stacking of elemental layers alongthe [001] direction, is attractive candidate for many advancedmagnetics material applications, such as high density magneticrecording media. The stacking fault effects on free surfaces wasexamined by first-principles calculations based on densityfunctional theory (DFT), within the pseudopotential plane wavemethod as implemented in VASP (Vienna Ab initio SimulationPackage). The projector augmented wave method with exchangecorrelation function is used for spin polarized generalizedgradient approximation (GGA). The layer atomic relaxation forfree surfaces show a compression on the relative displacementamount to about 1.35 %, 9.02 % for Fe and FeFe surfacesrespectively, the magnetic moment decrease about 3.90 % forFeFe surfaces. Voir les détails
Mots clés : L1 0 FePt, FePt; stacking fault, free surfaces
Expertise sur l’usure d’un outil de forage pétrolier à tète d’acier et caractérisation physico-chimique des multi-matériaux (Acier/CA/rechargement dur/ brasure)
Dans l’industrie pétrolier, les outils PDC sont les plus adaptées au forage des profiles tendres à mi-durs [1]. L’avancée technologique dans l’usinage numérique et la maitrise des paramètres relatifs à la projection thermique et au rechargement dur ont permet d’avantager l’outil PDC en corps acier sur l’outil matrice. Les performances de ce type d’outil et le comportement en service dans des conditions d’usure sévères dépendent étroitement de la cohésion des interfaces considérées formant le multi-matériau. Le travail consiste à élaborer et caractériser des multimatériaux semblables à ceux constituant la partie active de l’outil monobloc en PDC, où nous nous intéresserons à l’évolution microstructurale et les propriétés mécaniques de ces derniers réalisés successivement par les procédés de projection thermique, de rechargement dur et de brasage. Voir les détails
Mots clés : Outil de forage (PDC), expertise, usure, projection thermique, rechargement dur, brasage.
The effect of theartificial aging on the precipitation kinetic in the Al-Mg-Sialloy
In this study, the effect of the artificial aging on the kinetics of the precipitationprocesses in the Al-Mg-Si alloy was investigated by differential scanning calorimetry andhardness examinations.This investigation revealed that the artificial aging has apositive effecton the precipitation kinetic.The activation energy of the precipitation process was calculatedusing Kissinger model. The result of this studyshowed a change in hardness values and in theactivation energy for all precipitated phases. The hardness have high values at the higheraging temperature. The activation energy of the metastable phase is determined as 41.55,which indicate that the formation of this phase isuncomplicatedduring artificial aging. Voir les détails
Mots clés : Al-Mg-Si, Precipitation, kinetic, DSC.
Effect Of Precipitation Processes In AluminumAlloy 6101 T1Used In The Electric TransmissionLines
Many experiments are performed on aluminumalloy 6101 T1 to characterize the processes of precipitateovercoming by the dislocations. IT has been well known thatthe nuclei of metastable phases and composition fluctuation arefound in an Al- MgSi alloy during the early stage of aging. Thecombined effects of high temperature and the cold drawing ofthis alloy causeda highest microhardness of the materialaccompanied by a development of a fibrous texture. Theelectrical resistivity of the alloy decrease with the increasingaging time. Voir les détails
Mots clés : aging, dislocations, Aluminum alloy, Microhardness, Electrical resistivity