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International audience; Ti-V-Nb-Cr alloys have been reported as potential candidates for hydrogen storage applications. Investigating the processes of absorption and desorption is paramount to understand the hydrogen storage properties of these novel alloys and to develop more efficient hydrogen storage materials. In this work, we investigated the hydrogen absorption/desorption reactions of the (TiVNb)85Cr15 BCC multicomponent alloy by laboratory and synchrotron X-ray diffraction, Pair Distribution Function (PDF) analyses, Transmission Electron Microscopy (TEM) and thermo-desorption analyses (TDS). Hydrogen absorption behavior was studied by pressure-composition-isotherm (PCI) at room temperature, which demonstrated levels of absorption around 2 H/M (H/M = hydrogen-to-metal ratio) with low equilibrium pressure. The results showed a multi-step hydrogenation process: alloy ↔ BCC solid solution ↔ BCC intermediate hydride ↔ FCC dihydride. PDF analyses showed that the partially hydrogenated alloy at different levels of H/M and the fully hydrogenated alloy can be reasonably described by models with phases presenting random atomic distribution in the metal crystallographic sites. Moreover, the partially hydrogenated sample prior to the complete formation of the intermediate hydride showed evidence of two co-existing BCC phases.

The applicability of an alloy as a hydrogen storage media mostly relies on its pressure-composition-temperature (PCT) diagram. Since the PCT diagram is composition-dependent, the vast compositional filed of high entropy alloys, complex concentrated alloys or multicomponent alloys can be explored to design alloys with optimized properties for each application. In this work, we present a thermodynamic model to calculate PCT diagrams of body-centered (BCC) multicomponent alloys. The entropy of the phases is described using the ideal configurational entropy for interstitial solid solutions with site blocking effect. As a first approximation, it is assumed that the H partial molar enthalpy of a phase is constant, so the enthalpy of H mixing varies linearly with the H concentration. Moreover, the H partial enthalpy of a phase for a multicomponent alloy was approximated by a simple ideal mixture law of this quantity for the alloy’s components with the same structure. Experimental data and DFT calculations were used for parametrization of the enthalpy terms of eight elements (Ti, V, Cr, Ni, Zr, Nb, Hf, and Ta), which are the components of the alloys tested in this work. Experimental PCTs of six BCC multicomponent alloys of four different systems were compared against the calculated ones and the agreement was remarkable. The model and parameters presented here can be regarded as a basis for developing powerful alloy design tools for different hydrogen storage applications.

International audience; The applicability of an alloy as a hydrogen storage media mostly relies on its pressurecomposition-temperature (PCT) diagram. Since the PCT diagram is compositiondependent, the vast compositional field of high entropy alloys, complex concentrated alloys or multicomponent alloys can be explored to design alloys with optimized properties for each application. In this work, we present a thermodynamic model to calculate PCT diagrams of body-centered (BCC) multicomponent alloys. The entropy of the phases is described using the ideal configurational entropy for interstitial solid solutions with site blocking effect. As a first approximation, it is assumed that the hydrogen partial molar enthalpy of a phase is constant, so the enthalpy of hydrogen mixing varies linearly with the hydrogen concentration. Moreover, the hydrogen partial enthalpy of a phase for a multicomponent alloy was approximated by a simple ideal mixture law of this quantity for the alloy's components with the same structure. Experimental data and DFT calculations were used for parametrization of the enthalpy terms of eight elements (Ti, V, Cr, Ni, Zr, Nb, Hf, and Ta), which are the components of the alloys tested in this work. Experimental PCTs of six BCC multicomponent alloys of four different systems were compared against the calculated ones and the agreement was remarkable. The model and parameters presented here can be regarded as a basis for developing powerful alloy design tools for different hydrogen storage applications.

International audience; Grain 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.

Nano-mousses métalliques-Structure et élaboration Cet article est issu de : Matériaux | Matériaux fonctionnels-Matériaux biosourcés par Yannick CHAMPION Résumé Les nano-mousses métalliques sont des matériaux cellulaires présentant des taux de porosité supérieurs à 50 % et des dimensions structurales nanométriqueslongueur et diamètre de ligament, taille de pores, taille de grains, épaisseur de paroisqui leur confèrent des propriétés nouvelles. Cet article présente les caractéristiques structurales des nano-mousses, exploitées pour concevoir les matériaux, pour comprendre et pour optimiser leurs propriétés. Les méthodes d'élaboration sont ensuite détaillées dont la dissolution sélective d'alliage et le dépôt métallique sur un gabarit. Les principales propriétés et perspectives d'applications sont abordées.

Spark plasma sintering (SPS) of metallic glasses (MG) can be quite different from sintering crystalline metallic alloys. Indeed, MG behave differently with increasing temperature, as they encounter a glass transition and devitrification. Their shaping can thus be compared to what can be performed on thermoplastic polymers. SPS is a promising way to prepare bulk parts from amorphous powders, since it allows very fast heating and cooling rates. It gives an advantage to avoid or limit devitrification of the amorphous phase upon the thermal cycle. However, diffusion mechanisms, which generally control densification, are activated at temperatures that are not compatible with MG structural integrity. From a manufacturing point of view, one has thus to find the best compromise to achieve full density and optimal properties without degrading the amorphous phase.

A silver-based nanoporous material was produced by dealloying (selective chemical etching) of an Ag38.75Cu38.75Si22.5 crystalline alloy. Composed of connected ligaments, this material was imaged using a scanning electron microscope (SEM) and focused ion-beam (FIB) scanning electron microscope tomography. Its mechanical behavior was evaluated using nanoindentation and found to be heterogeneous, with density variation over a length scale of a few tens of nanometers, similar to the indent size. This technique proved relevant to the investigation of a material&rsquo, s mechanical strength, as well as to how its behavior related to the material&rsquo, s microstructure. The hardness is recorded as a function of the indent depth and a phenomenological description based on strain gradient and densification kinetic was proposed to describe the resultant depth dependence.

International audience; In this study, the MgAlTiFeNi high entropy alloy was processed by high-energy ball milling under both argon and hydrogen atmospheres. It is shown that this alloy forms a body-centered cubic (BCC) structure when milled under an argon atmosphere (mechanical alloying-MA) and a combination of BCC, FCC, and Mg2FeH6 when milled under hydrogen pressure (reactive milling-RM). The hydrogen storage behavior of the RM-MgAlTiFeNi samples was evaluated by a combination of thermal analyses and manometric measurements in a Sieverts apparatus. The RM-MgAlTiFeNi alloy presented an initial functional hydrogen storage capacity of 0.87 wt%, which increased to 0.94 wt% after the second absorption. Also, it exhibited a high hydrogen absorption and desorption kinetics at temperatures 100 °C lower than the one for the desorption temperature of the commercial MgH2. Electrochemical discharge of RM-MgAlTiFeNi samples showed precisely the same hydrogen content as that obtained in the gas desorption. Electrochemical charging/discharging experiments were also performed in the MA-MgAlTiFeNi samples, which presented lower electrochemical storage capacity, a behavior probably resulting from the instability of the alloy in the alkaline solution with the formation of a hydroxide layer on its surface that hinders the electrochemical reactions

In order to systematically compare high entropy alloys (HEA) and conventional diluted multi-component alloys and to observe the transition between both, 13 CrxMnxFexCoxNi100 − 4x multi-component alloys, where x takes values between 2 and 25, were processed so as to reach the stable state and then characterized. A unique fcc solid-solution is formed for a wide range composition, spanning from 0 to 90 at.% of Cr, Mn, Fe and Co. When the sum of Cr, Fe, Mn and Co contents is larger than 90 at.%, the system demixes into two quaternary phases. The existing thermodynamics models are unable to predict the range of existence of the solid-solution for the studied alloys. No microstructural transition between HEA and conventional diluted alloys is observed. The maximization of configurational entropy appears to be neither a sufficient nor a necessary condition to form a HEA. Consequently a new definition for HEA is needed. Keywords: Multi-component alloys, High entropy alloys, Solid solution, Microstructure, Thermodynamic modelling

International audience; • Nanoindentation strain rate jump tests of 3 BMGs and 3 BMGCs • Development of new method to determine activation energy and volume of shear transformation zones • Testing temperature strongly influences activation energy and volume • Rejuvenation (by HPT and thermal cycling) does not influence activation energy and volume G R A P H I C A L A B S T R A C T a b s t r a c t Nanoindentation strain-rate jump testing was used to determine activation volumes and energies of various metallic glasses and composites. Three different single phase metallic glasses and three composites (two with amor-phous/crystalline Cu and one with an amorphous/amorphous structure) were investigated. The state of the materials was additionally changed by varying the testing temperature between room temperature and 430 °C, by performing high pressure torsion and by thermal cycling. The results show that testing temperature is the main parameter controlling activation volume and energy, whereas material modifications by high pressure torsion and thermal cycling do not significantly affect them.

The aim of this study is to show that new types of bulk metallic glass composites (BMGCs) can be produced via severe plastic deformation (SPD). The initial materials are mixtures of a Zr-metallic glass (MG) and crystalline Cu powders that were mixed and then consolidated, cold welded together and refined by high pressure torsion (HPT). Four different compositions (Zr-MG Xwt% Cu, X = 20, 40, 60, 80) were produced as well as single phase Zr-MG samples as reference. To investigate the influence of the degree of deformation and the ratio of the two phases on the evolution of the microstructure and mechanical properties, scanning electron microscopy (SEM), X-ray diffraction (XRD), hardness and microcompression measurements were used.

International audience; Keywords: A metallic glass B mechanical properties B phase stability B bonding C severe plastic deformation D microstructure A B S T R A C T Two different metallic glass powders were consolidated and deformed via high-pressure torsion to synthesize amorphous dual phase composites. The influence of volume fraction of the two amorphous phases and the applied shear strain was investigated. By varying the applied strain, the dimensions of the phases could be systematically varied from the micro-to the nanometer regime and at the highest applied strain even a transition to a single phase state could be observed. The study illustrates the potential of producing novel bulk metallic glasses by deformation-induced mixing which are not accessible by the classical casting route.

The deformation micro-mechanisms of an as-cast equimolar refractory high-entropy alloy composed of Ti, Zr, Hf, Nb and Ta are analyzed by monotonic and relaxation compression tests coupled to transmission electron microscopy observations. The evolution of the work hardening with plastic strain displays 3 stages. After a sharp decrease until a plastic strain of approximately 3%, work hardening stabilizes at 1300±50 MPa and finally decreases again. The measured apparent activation volumes V a p p * slightly evolve with plastic strain and decrease from approximately 50b3 to 30b3. These values are coherent with a Peierls mechanism due to strong intrinsic lattice friction. In addition, the measured activation volumes correlate well with TEM observations, which give evidence that dislocation glide is controlled – in the first stages – by the movement of screw dislocations. The deformation is rapidly localized in bands in which dislocation dipoles, loops and tangles are induced at higher plastic strains.

The aim of this study was to show the possibility to produce bulk metallic glass with severe plastic deformation. High pressure torsion was used to consolidate Zr-based metallic glass powder and deform it further to weld the powder particles together. The produced samples were investigated with Scanning electron microscope (SEM), Transmission electron microscope (TEM), Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) to check if the specimens are fully dense and have an amorphous structure. The results show that the specimens remain amorphous during high pressure torsion and the density depends on the applied strain. Additional Vickers hardness measurements enable a comparison with literature and show for Zr-based metallic glass powder typical values (approximately 500 HV).

SUMMARY A model, which takes into account the indentation size effect, was proposed to relate hardness and its standard deviation to the quality of the sample surface, i.e., the roughness and the tilt. Stainless steel samples were mechanically polished so as to obtain various roughness and tilt. Then the quality of the surface and the hardness were measured respectively by scanning probe microscopy and by nanoindentation. The model was fitted according to those experimental data. It was shown that the standard deviation only depends on the ratio of the arithmetic roughness over the contact depth of the indent while the average hardness also depends on the contact depth and on the tilt. It was deduced that hardness measurements are performed with an uncertainty lower than 10% if: (i) the ratio of the arithmetic roughness over the contact depth of the indent is lower than 0.05, (ii) the tilt of the sample is lower than 2° and (iii) the difference of roughness between samples is lower than 50%. SCANNING 37:350–360, 2015. © 2015 Wiley Periodicals, Inc.

Copper nanopowders were sintered using Spark Plasma Sintering (SPS). Special attention was paid to the presence of natural surface oxide and reductive thermal treatments under H 2 atmosphere were carried out to remove it. The sintering mechanisms were investigated by the means of disrupted experiments at various temperatures to reach different shrinkage rates. Optimized experiments were also carried out to reach a maximum densification. The samples were characterized and compared using density measurement, X-ray diffraction, mechanical tests (tension and compression) and analysis of the fracture surfaces with scanning electron microscope. On the one hand, it results that during the SPS treatment, the raw powder undergoes a series of oxide transformations from CuO to Cu 2 O. On the other hand, reductive treatment drastically decreases the sintering temperature, from 650 °C to 260 °C, to reach 90% density without grain growth. Higher mechanical strength, up to 750 MPa, also shows better consolidation.

The microstructure and mechanical properties were investigated in an industrial Al-Cu-Mg alloy processed by Equal Channel Angular Pressing ECAP and heating. The die used is formed by two channels intersecting at an angle 90°. Transmission Electron Microscopy (TEM) and orientation (ASTAR) imaging were used in addition to hardness measurements. After heating, a sub-micron grain size is retained. In addition, a further hardening is observed due to secondary precipitation. Differential Scanning Calorimetry (DSC) showed that the activation energy of θ’ precipitation is strongly lowered after ECAP.

To study the evolution of structural and mechanical properties with composition, 10 Cr x Mn x Fe x Co x Ni 100-4x alloys were processed and characterized by X-ray diffraction and nanoindentation. Those alloys are all single-phase solid-solutions and their composition ranges from conventional diluted multi-component alloys (MCA) to high entropy alloys (HEA). The lattice parameter and the hardness were measured and were compared to existing models. The hardest studied alloy turns out to be the non-equimolar Cr 10 Mn 10 Fe 10 Co 10 Ni 60 . More precisely, it was shown that, when the composition evolves from diluted MCA to HEA: (i) the lattice parameter increases and follows a Vegard's law up to 4x=40 at%; (ii) the hardness increases and follows a Mott-Nabarro-Labush law up to 4x=40 at% and then decreases. This breakpoint of the evolution of both lattice parameter and hardness at 40 at% is proposed as the transition between conventional diluted multi-component solid solutions and HEA.

An analytical model is proposed to quantitatively describe the depth-dependence of Vickers micro-hardness in metallic glasses. The approach is based on a shear bands distribution-induced strain gradient during testing and was used to analyze thermal relaxation in the Zr55Cu20Al10Ni10Ti5, Ni53Nb20Zr8Ti10Co6Cu3, and Mg65Cu12.5Ni12.5MM10 metallic glasses. It was shown that a decrease of the free volume leads systematically to a decrease of the alloy hardness. This analysis also gives an evaluation of the shear band thickness and the role of the elastic properties in the depth-dependence of the Vickers micro-hardness.

The aim of this study was to evaluate the possibilities offered by severe plastic deformation to prepare nanoscaled composites based on a bulk metallic glass. High pressure torsion was applied to a mixture of aluminium and metallic glass powders to process a composite at the nanoscale. Ultimate mixing of the two phases was achieved for a very large level of deformation resulting in a fully amorphous structure. Using analytical scanning transmission electron microscopy, nanoscaled chemical gradients were clearly exhibited. The very high strength (HV ~ 700) of the final metallic glass is attributed to this unique nanoscaled composition modulated structure. The role of shear bands both in the partial mixing and in the amorphization mechanism is discussed on the basis of a simple geometrical model.

One of the most widely used approaches to model metallic-glasses high-temperature homogeneous deformation is the free-volume theory, developed by Cohen and Turnbull and extended by Spaepen. A simple elastoviscoplastic formulation has been proposed that allows one to determine various parameters of such a model. This approach is applied here to the results obtained by de Hey et al. on a Pd-based metallic glass. In their study, de Hey et al. were able to determine some of the parameters used in the elastoviscoplastic formulation through DSC modeling coupled with mechanical tests, and the consistency of the two viewpoints was assessed.

The substitution of Y by mischmetal was investigated on the Mg 65 Cu 25 Y 10 metallic glass, in order to reduce pure rare earth content and improve manufacturing for potential applications. Works showed that this substitution is well accommodated by partial substitution of Cu by Ni. Alloys were prepared by planar flow melt spinning, with various amounts of mischmetal (0, 5 or 10 at.%) and Ni (0, 5, 12.5, 20 or 25 at.%). With increasing content of mischmetal and nickel, the glass forming ability, especially the width of the supercooled liquid region tends to decrease. However, an optimal substitution of Cu by Ni (12.5 at.%) in an alloy free from Y has been identified to present an appreciable glass forming ability with a supercooled liquid region of 35 K.

Planar flow melt spinning was used to prepare six Zr-based metallic glasses. Evidence of the effect of chemistry was found by structural and thermal characterizations. A clear influence of chemistry was also observed on the mechanical behaviour, with differences in hardness and Young’s modulus measured by nanoindentation being noted. Using a statistical analysis of the data, the activation volume controlling initiation of shear bands in the localized deformation process was obtained, and a correlation between this volume and the intrinsic alloy properties is emphasized.

Low temperature (77 K, 243 K and 255 K) mechanical tests were carried out at strain rates between 7.10 −4 s −1 and 5.10 −2 s −1 on pure ultrafine grained (UFG) copper (grain size 100 nm) to mimick room temperature high strain rates. Variation of the activation volume measured as a function of the stress is consistent with the analytical model proposed in [C. Duhamel, Y. Brechet, Y. Champion Int. J. Plast. 26 (2010) 747–757] to explain the rheology of UFG metals. This model is based on dislocations interactions at grain boundaries and grain boundaries sliding. The experiments confirm that the strain rate sensitivity (which should be a criterion for plasticity in absence of macroscopic work hardening) increases with the strain rate (or stress) at high strain rate, as also observed for nanotwinned copper. From the model, a strain rate sensitivity criterion is derived, function of a characteristic UFG strength parameter and grain boundary properties. The analytical description of deformation of UFG including microstructural properties should help for a quantitative control of the macroscopic properties of UFG.

Self-supporting porous silver foils with an average pore size

Ultrafine grained (UFG) copper with an average grain size of 115 nm was micro-alloyed with silver (UFG CuAg) to analyze its effect on strain rate sensitivity. The materials were prepared by sintering Ag microalloyed-Cu ultrafine powder, using the spark plasma sintering (SPS) technique and after H2 pre-annealing for oxide reduction. Mechanical tests show that UFG CuAg follows the law of behavior established for UFG Cu: m ≈ B ( 1 − σ 0 / σ ) , relating the strain rate sensitivity m and the applied stress, σ . In this relation, σ 0 is a threshold grain size dependent stress and B is characterizing the grain boundaries diffusion properties. Main difference compared to pure UFG copper is a large value of the parameter B for UFG CuAg, indicating a dominant role of the grain boundaries structure and chemistry on the rheology of UFG metals.

The microstructural evolution of a recycled aluminum alloy after equal channel angular pressing (ECAP) up to four passes was investigated using X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM). Microhardness tests were performed to determine the associated changes in mechanical properties. An ultrafine-grained material has been obtained with a microstructure showing a mixture of highly strained crystallites. A high density of dislocations was achieved as a result of severe plastic deformation (SPD) through the die. Changes in mechanical behavior are also revealed after ECAP due to strain hardening. Thermal analysis and TEM micrographs obtained after annealing indicate the succession of the recovery, recrystallization, and grain growth phenomena. Moreover, the energy stored during ECAP may be related to the dislocation density introduced by SPD. We finally emphasize the role played by the precipitates in this alloy.

Composites with volume fraction from 10 vol.% to 90 vol.% were prepared by spark plasma sintering (SPS) of mixing of aluminium and metallic glass (Zr57Cu20Al10Ni8Ti5) powders with similar particle size. These materials show gradual evolution of their mechanical behaviour. First, monotonous but non linear variation of the strength is observed. That reveals two different mechanisms describing the dependence of strength with the composition and architecture. Second, stress–strain curves successively show, from low to high Al content, absence of plasticity, plasticity with intensive decrease of strength related to local damaging, and finally plasticity with work hardening. The mechanical behaviour evolutions are geometrically and analytically modelled. This reveals change in behaviour at the expected 3-dimensional percolation thresholds for a random spatial distribution of two phases.

Development of metallic glasses is hindered by the difficulties in manufacturing bulk parts. We report on the preparation of glassy alloys using the spark plasma sintering of gas atomized powders. The Zr57 Cu20 Al10 Ni8 Ti5 alloy processed has a high glass forming ability. Densification is obtained at the glass transition temperature (390 °C) under high pressure (≈500 MPa). Systematic study of the effect of powder particles size and sintering time is performed through structural and thermal analyses. Local and partial devitrification of the amorphous alloy is detected, resulting from local temperature overshoots. From these analyses, an approach of the spark plasma sintering mechanism of metallic glasses is proposed.

Development of metallic glasses is hindered by the difficulties in manufacturing bulk parts. In this paper, we report on the fabrication of glassy alloys using the spark plasma sintering of gas atomized powders. The Zr-based processed alloy has a high glass forming ability. Its densification is obtained at the glass transition temperature (390 °C) under high pressure (≈ 500 MPa). Systematic study of the effect of powder particle size and sintering time is performed through structural and thermal analyses. Local and partial devitrification of the amorphous alloy is detected, resulting from local temperature overshoots. From these analyses, an approach of the spark plasma sintering mechanism of metallic glasses is proposed.

Spark plasma sintering (SPS) was used to sinter gas-atomized Zr 57 Cu 20 Al 10 Ni 8 Ti 5 amorphous powder. Systematic analyses were performed to study particle size and annealing time effects on the parts structure and properties. Partial devitrification and particles welding were observed and correlated to particle size and thermal conditions. Mechanical testing, through compression and micro-hardness, reveals that the sintered parts show strength similar to a quenched bulk metallic glass and damaging before failure. However, the pulsed current input does not seem the most relevant way to sinter amorphous powders: during the sintering initial stages (when necks are small), excessive over-heating is generated in the vicinity of particles necks, and is responsible for partial devitrification; further current input at large necks leads to complete densification. Effects of the stress, the thermo- and electro-transports on the sintering are evaluated to provide a better understanding of the SPS mechanisms of densification of metallic glasses.

The microstructure of a promising equimolar refractory high-entropy alloy containing Ti, Zr, Hf, Nb and Ta has been investigated after arc melting and induction techniques. The high-entropy alloy displays a fully disordered bcc crystal structure. At the nanoscopic scale, the observed dislocations appear mainly patterned in sub-grain boundaries in the solid solution. At the mesoscopic level and following the cooling rate, the solidified microstructure is different: the alloy exhibits a dendritic structure with the presence of Ti, Zr and Hf-rich microsegregations in the interdendritic zones for the slowest cooled parts, whereas it is fully homogenized in the regions for which the cooling rate is intense.

Copper based materials are still the most attractive low resistivity materials for microelectronics and electrotechnics applications, though, all variants developed to combine strength and conductivity, such as solid solutions and composites, suffer from decay in electric conductivity while strength is increased . In a addition, linear decay was also conjectured for pure copper when grain size is refined below the UFG and nanostructured domains (except when grain boundaries are pure twins). Copper alloys with low content of silver and chromium were prepared by high pressure torsion (HPT) with various annealing conditions. Vickers hardness and electric resistivity in the temperature range of 4K-340K, were measured as well as microstructural characterizations were performed using quantitative X-ray diffraction. Depending on the annealing conditions the alloys exhibit from 25% to 75% of IACS electric conductivity at room temperature and hardness in the range of 200 Hv. Origins of both high strength and high electric conductivity were investigated from microstructures analysis, using transmission electron microscopy and mechanical testing.

TEM investigation was performed on a recycled aluminum processed by Equal Channel Angular Extrusion. The aluminum contains many inclusions which were identified to be rich in iron and silicon.This has a substantial effect in dragging recovery. ECAE was performed via routes B and C using a die formed by two channels characterized by the well defined angles =90° and  = 90°. The evolution of the microstructure seems to be similar whether using route B or C. a high dislocation density was introduced since the first passage together with a high density of Frank dislocation loops. The latter are due to a by-passing of inclusions by cross-slip mechanism. Weak beam experiments enable us to investigate the early stages of recovery consisting in the formation of dislocation walls and few dislocation cells. A partial arrangement of dislocations was observed since the first passage through the die. The formation of dislocation cells began already before annealing and progresses at more elevated temperatures. The substantive recovery seems to push recrystallization process to high temperatures. By contrast, DSC investigations show a significant difference: The amount of energy deduced from the area of the peak relative to recrystallization is higher when using route C.

Equal channel angular extrusion (ECAE) of aluminum alloys leads to enhanced strength. However, the effects of processing route on the resulting properties were not extensively investigated, and sometimes neglected. In the present work, an aluminum was processed by ECAE via routes B C and C using a die formed by two channels connected at an angle Ф = 90°. Coherency lengths D calculated from X-ray diffraction peaks were 85 nm after the first passage. For route B C , it was kept constant when the number of passages N was increased. For route C, an increase of D was observed when increasing N . The remaining densities of dislocations ρ were calculated using a recently published formula. A decrease of ρ was observed during ECAE in route C but not in route B C . Mechanical tests allowed us to relate the increase of D and the decrease of ρ to an enhanced recovery during ECAE via route C.

Equal channel angular pressing (ECAP) is a well-known method to obtain high hardness levels through a strong refinement of grains. To obtain fine grains, a subsequent heating is performed after deformation. The main difficulty is to retain a sufficiently small grain size. Alloy purity is an important parameter in recristallization kinetics. In the present work, an industrial and a recycled Al-4%Cu alloys were subjected to ECAP. The evolution of the microstructure of the deformed and annealed alloys was investigated. The alloys exhibit different hardness values for a given equivalent deformation. In industrial alloy, no recovery was observed at low temperatures. On the other hand, enhanced precipitation in this alloy leads to an increase in hardness balancing then softening due to recovery. A substantial decrease in hardness is observed around 250 ∘ C and seems to depend on alloy purity.