Evolution de la microstructure et des proprietes mecaniques d'alliages Ni-Al-Ti par vieillissement thermique et sous irradiation

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Transition from intergranular to pitting corrosion in fine grained aluminum processed by equal channel angular pressing

International audienceEqual Channel Angular Pressing (ECAP) is used to improve the strength of metallic materials by grain refinement. Moreover, extensive applications become possible by combining high strength with good surface properties. In the present work, the effect of ECAP on the corrosion behavior of aluminum was investigated in a 3% NaCl medium. From electrochemical experiments, microscopic and topographic observations, we have shown that, corrosion is mainly intergranular in the coarse grained material. After ECAP, a clear pitting is observed. We related this to a destruction of the preexisting grain boundaries and to the homogenization of the microstructure achieved by ECAP

Corrosion properties of anodized aluminum: Effects of equal channel angular pressing prior to anodization

International audienceMany aluminum alloys are subjected to mechanical treatments before anodization. We have studied the effects of Equal Channel Angular Pressing (ECAP) on the properties of the passive film of aluminum 99.1%. Electrochemical measurements and micrography were used for characterisation. In 3% NaCl solution, anodization after ECAP leads to higher free potential values than that without deformation. Grain refinement and high dislocation density obtained by ECAP enhance the formation of a more continuous film after anodization. The destruction of inclusions increases pitting site density and leads to low-depth pits. The role of inclusions and pit sizes in the repassivation is illustrated

EBSD, XRD and SRS characterization of a casting Al-7wt%Si alloy processed by equal channel angular extrusion: Dislocation density evaluation

International audienceAluminum-silicon (AleSi) alloys of high silicon contents are composite materials; they are used whenever high casting properties are required. They are slightly ductile below 8wt%Si. An increase in ductility can be obtained by refining Si-crystals in elaboration or by a further hot working. In the present work, an Al-7wt%Si alloy was processed by Equal Channel Angular Extrusion (ECAE) at temperatures 20 °C and 160 °C up to three passes. The die was formed by two cylindrical channels with characteristic angles Φ = 110°and Ψ = 0. EBSD, X ray diffraction (XRD) and Strain Rate Sensitivity (SRS) were used to characterize the microstructure and the mechanical properties. High levels of strain were introduced at both temperatures. The activation volume was lowered to 125b 3 and 210b 3 at 20 °C and 160 °C respectively and was considered to be dislocation density dependent. The remaining dislocation densities calculated from EBSD, XRD and SRS experiments are quite different. This was explained by the scale difference and by the sensitivities of the methods to the free surface effect

Orientation imaging- ASTAR investigation of the grain and precipitate morphology in Al–Cu–Mg alloy processed by Equal Channel Angular Pressing

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Activation volume and the role of solute atoms in Al-Mg-Si alloy processed by equal channel angular extrusion

International audienceGrain refinement to the sub-micron scale was found to enhance both strength and plasticity. In this size range, the micro-mechanisms of deformation are not yet sufficiently specified. In the present work, strain rate sensitivity was investigated in an Al-Mg-Si alloy processed by equal-channel angular extrusion. The microstructure was controlled by conventional transmission electron microscopy and orientation imaging-ASTAR. In the as-quenched state, deformation produces grains below 100 nm in size. The activation volume V was reduced to 70b 3. Based on published theoretical models, we have shown that in such alloy, pure grain boundary sliding cannot be revealed in the low-stress range, due to the intervention of solute atoms. Beyond, the stressdependence of V consists with an inverse Cottrell-Stokes behavior. This trend was confirmed by TEM which revealed dislocation activity and grain boundary emission. Ageing at 150 °C increases the contribution of GBS whereas the residual activation volume continues to be leveled

Annealing Effects in Nanograined Al-Cu-Mg Alloy Processed by Equal Channel Angular Pressing

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DVZ-based Obstacle Avoidance Control of a Wheelchair Mobile Robot

International audienceThis paper adresses the control problem of unicycle mobile robot evolving in unknown environments using reactive behaviours. The deformable Virtual Zone (DVZ) principle is used to resolve this problem through defining a safety zone around the vehicle. This approach presents fast control laws that react depending on the presence of an obstacle in the safety zone. Experimental tests are carried out on a wheelchair mobile robot and proved the effectiveness of the studied method

Microstructure et volume d'activation d'un laiton Cu-6%Zn traité par ECAP

International audienceThe generation of a high density of twins few tens nanometers in size can enhance both strength and ductility. The present work aims to produce highly twinned microstructure in Cu-6wt% Zn alloy of a moderate stacking fault energy (SFE) by equal channel angular pressing (ECAP) using a die with angles =110° and =0. X ray diffraction (XRD) shows that a high density of defects is stored up to 2 passes then a recovery takes place. EBSD imaging reveals a high density of twins and a fibrous microstructure. Grains close to 100nm in size are formed. Strain rate sensitivity (SRS) was investigated in compression and nanoindentation (NI). Compression curves show that deformation occurs by slipping with a contribution of twins to hardening. A high contribution of shear bands was revealed during ECAP and compression tests. The activation volume V* in compression and NI is in the range 70b 3-100b 3 , consistent with the emission of dislocations from grain boundaries and twin boundaries The experimental values of V* were compared to those expected from defect densities