28 research outputs found
Microstructure and mechanical properties of AA6082-T6 by ECAP under warm processing
An AA6082 alloy deformed by equal channel angular pressing (ECAP) was studied. The evolution of microstructure as a function of the strain imparted was evaluated by optical microscopy (OM), scanning electron microscopy (SEM) coupled with an electron backscattered diffraction (EBSD) detector, X-ray diffraction (XRD) and Differential Scanning Calorimetry (DSC). XRD showed that MgSi2 precipitates developed in the ECAPed specimens. Texture analysis showed the apparition of two types of textures, one associated with shearing deformation and the second due to the recrystallization phenomena. Mechanical strength properties measured by tensile tests increased in the first ECAP pass, and then progressively diminished. This phenomenon was associated to the activation of continuous softening phenomena. Calorimetric analysis indicated a slightly rise in the recrystallization temperature of the deformed specimens. Also, the stored energy increased with rising ECAP passes due to the production of new dislocations. The average geometrically necessary dislocation (GND) density, measured by EBSD, increased with increasing ECAP passes. However, the rate of increase slows down with the progress of ECAP passes.Peer ReviewedPostprint (author's final draft
Microstructure and Mechanical Properties of AA6082-T6 by ECAP Under Warm Processing
An AA6082 alloy deformed by equal channel angular pressing (ECAP) was studied. Microstructural evolution of the alloy processed by ECAP with different passes were evaluated by using optical microscope, scanning electron microscopy coupled with an electron backscattered diffraction (EBSD) detector and X-ray diffraction. Texture analysis showed the apparition of two types of textures, one associated with shearing deformation and the second due to the recrystallization phenomena. Mechanical strength properties measured by tensile tests increased in the first ECAP pass, and then progressively diminished due to the presence of concurrent softening phenomena. Calorimetric analysis indicated a slightly increase in the recrystallization temperature of the deformed specimens. Also, the stored energy increased with increasing ECAP passes due to the production of new dislocations. The average geometrically necessary dislocation density, measured by EBSD, increased with increasing ECAP passes. However, the rate of increase slows down with the progress of ECAP passes.Fil: Khelfa, T.. Northwestern Polytechnical University; China. University of Sfax; TĂșnezFil: Muñoz Bolaños, Jairo Alberto. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Rosario. Instituto de FĂsica de Rosario. Universidad Nacional de Rosario. Instituto de FĂsica de Rosario; Argentina. Universidad PolitĂ©cnica de Catalunya; EspañaFil: Li, F.. Northwestern Polytechnical University; ChinaFil: Cabrera -Marrero, J. M.. Universidad PolitĂ©cnica de Catalunya; EspañaFil: Khitouni, M.. University of Sfax; TĂșne
Plastic behavior and microstructure heterogeneity of an AA6063-T6 aluminium alloy processed by symmetric and asymmetric rolling
Rolling is one of the most employed industrial processes which can be used at multiple manufacturing stages, allowing different geometries such as plates, rods, profiles, billets, slabs, tubes, and seamless tubes to be obtained. However, rolled products develop anisotropy due to the preferential orientation of crystals in the rolling direction. Thus, some process configurations and different processing parameters (e.g., thickness reduction per rolling pass, deformation routes, roll diameters, and strain rate) have been proposed to deal with the desired anisotropy. In this context, this investigation evaluates and compares the effect of symmetrical and asymmetrical rolling on an aluminum alloy sheet deformed until a 38% thickness reduction using multiple rolling passes. The asymmetrical process displayed larger texture and microstructure gradients across the sheet thickness than the symmetrical one, manifested as more grain refinement and more intense shear texture components close to sheet surfaces. In terms of plastic anisotropy, the visco-plastic self-consistent model predicted higher average anisotropy for the symmetric rolling than the asymmetric process due to a strong combination of recrystallization and deformation texture components. Conversely, the asymmetric process showed lower planar anisotropy values due to the increase in the fraction of shear and deformation texture components near the sheet surfaces, producing a less intense overall texture than the symmetric rolling. The additional shear strain component was mainly responsible for the material strengthening and texture weakening after the asymmetrical rolling process. In addition, the shear strain produced grain refinement, decreased misorientation, and higher dislocation densities than the as-received and symmetrically rolled materials. After asymmetrical rolling, the microstructure and texture showed heterogeneous profiles across the sheet thickness. This gave rise to a heterogeneous grain size refinement, decreased misorientation close to sheet edges, and plastic gradients.Peer ReviewedPostprint (published version
Direct Observation of Propagating Gigahertz Coherent Guided Acoustic Phonons in Free Standing Single Copper Nanowires
We report on gigahertz acoustic phonon waveguiding in free-standing single
copper nanowires studied by femtosecond transient reflectivity measurements.
The results are discussed on the basis of the semianalytical resolution of the
Pochhammer and Chree equation. The spreading of the generated Gaussian wave
packet of two different modes is derived analytically and compared with the
observed oscillations of the sample reflectivity. These experiments provide a
unique way to independently obtain geometrical and material characterization.
This direct observation of coherent guided acoustic phonons in a single
nano-object is also the first step toward nanolateral size acoustic transducer
and comprehensive studies of the thermal properties of nanowires
Structure and microstructure evolution of Al-Mg-Si alloy processed by equal-channel angular pressing
An ultrafine grained AlâMgâSi alloy was prepared by severe plastic deformation using the equal-channel angular pressing (ECAP) method. Samples were ECAPed through a die with an inner angle of F = 90° and outer arc of curvature of Âż = 37° from 1 to 12 ECAP passes at room temperature following route Bc. To analyze the evolution of the microstructure at increasing ECAP passes, X-ray diffraction and electron backscatter diffraction analyses were carried out. The results revealed two distinct processing regimes, namely (i) from 1 to 5 passes, the microstructure evolved from elongated grains and sub-grains to a rather equiaxed array of ultrafine grains and (ii) from 5 to 12 passes where no change in the morphology and average grain size was noticed. In the overall behavior, the boundary misorientation angle and the fraction of high-angle boundaries increase rapidly up to 5 passes and at a lower rate from 5 to 12 passes. The crystallite size decreased down to about 45 nm with the increase in deformation. The influence of deformation on precipitate evolution in the AlâMgâSi alloy was also studied by differential scanning calorimetry. A significant decrease in the peak temperature associated to the 50% of recrystallization was observed at increasing ECAP passes.Peer ReviewedPreprin
Severe plastic deformation for producing superfunctional ultrafine-grained and heterostructured materials: An interdisciplinary review
Ultrafine-grained and heterostructured materials are currently of high interest due to their superior mechanical and functional properties. Severe plastic deformation (SPD) is one of the most effective methods to produce such materials with unique microstructure-property relationships. In this review paper, after summarizing the recent progress in developing various SPD methods for processing bulk, surface and powder of materials, the main structural and microstructural features of SPD-processed materials are explained including lattice defects, grain boundaries and phase transformations. The properties and potential applications of SPD-processed materials are then reviewed in detail including tensile properties, creep, superplasticity, hydrogen embrittlement resistance, electrical conductivity, magnetic properties, optical properties, solar energy harvesting, photocatalysis, electrocatalysis, hydrolysis, hydrogen storage, hydrogen production, CO2 conversion, corrosion resistance and biocompatibility. It is shown that achieving such properties is not limited to pure metals and conventional metallic alloys, and a wide range of materials are currently processed by SPD, including high-entropy alloys, glasses, semiconductors, ceramics and polymers. It is particularly emphasized that SPD has moved from a simple metal processing tool to a powerful means for the discovery and synthesis of new superfunctional metallic and nonmetallic materials. The article ends by declaring that the borders of SPD have been extended from materials science and it has become an interdisciplinary tool to address scientific questions such as the mechanisms of geological and astronomical phenomena and the origin of life
Ductility and plasticity of ferritic-pearlitic steel after severe plastic deformation
A ferritic-pearlitic steel was subjected to severe plastic deformation (SPD) through Equal Channel Angular Pressing (ECAP) at room temperature, obtaining strengths greater than 1 GPa. Steel constituents were identified by light microscopy displaying similar grain sizes around 14 ”m for the pearlite, and 13 ”m and 18 ”m for the ferrite before and after heat treatment, respectively. Texture changed from a rolling type to a simple shear texture with higher intensity after 4 ECAP passes. After different severe plastic deformation magnitudes, an ultra-fine grain structure was obtained with grain sizes between 0.9 ”m-0.36 ”m. The substantial grain size reduction was related to heterogeneous Geometrically Necessary Dislocations (GNDs) distribution in the as-received material with pearlite showing higher GNDs densities than ferrite. The remarkable strength increase after ECAP processing was found to be dependent on both small grain sizes and high dislocation densities. On the other hand, the low ductility of the ultrafine-grained (UFG) material was associated with a high annihilation rate of mobile dislocations at deformations greater than 0.39. Additionally, excellent plasticity properties were associated with a high density of immobile dislocations as well as high GND densities inside the deformed grains.Peer ReviewedPostprint (author's final draft
Electron microscopy investigation and Mossbauer properties in new LaBaFe0.5Zn0.5MnO6-delta perovskite compound
Structure and microstructure evolution of Al-Mg-Si alloy processed by equal-channel angular pressing
An ultrafine grained AlâMgâSi alloy was prepared by severe plastic deformation using the equal-channel angular pressing (ECAP) method. Samples were ECAPed through a die with an inner angle of F = 90° and outer arc of curvature of Âż = 37° from 1 to 12 ECAP passes at room temperature following route Bc. To analyze the evolution of the microstructure at increasing ECAP passes, X-ray diffraction and electron backscatter diffraction analyses were carried out. The results revealed two distinct processing regimes, namely (i) from 1 to 5 passes, the microstructure evolved from elongated grains and sub-grains to a rather equiaxed array of ultrafine grains and (ii) from 5 to 12 passes where no change in the morphology and average grain size was noticed. In the overall behavior, the boundary misorientation angle and the fraction of high-angle boundaries increase rapidly up to 5 passes and at a lower rate from 5 to 12 passes. The crystallite size decreased down to about 45 nm with the increase in deformation. The influence of deformation on precipitate evolution in the AlâMgâSi alloy was also studied by differential scanning calorimetry. A significant decrease in the peak temperature associated to the 50% of recrystallization was observed at increasing ECAP passes.Peer Reviewe
Microstructure and strengthening mechanisms in an Al-Mg-Si alloy processed by equal channel angular pressing (ECAP)
The microstructure, mechanical properties, and strengthening mechanisms of an Al-Mg-Si alloy (AA6060) subjected to severe plastic deformation using equal channel angular pressing (ECAP) were investigated. Samples were passed through a die with an inner angle of F = 90° and outer arc of curvature of Âż = 37° at room temperature up to 12 passes via route Bc. Electron backscatter diffraction (EBSD) was used to evaluate the microstructure and misorientation boundaries. The microstructure showed a large fraction of low-angle boundaries associated with subgrain formation in the first ECAP pass, while after eight and 12 passes, a heterogeneous ultrafine grain structure with an average grain size around 0.57 and 0.47 ”m, respectively, was obtained. In order to characterize the mechanical properties, microhardness and tensile tests were carried out. Results of mechanical property tests show that microhardness, yield stress, and ultimate tensile strength increase as ECAP pass number increases up to a maximum value of 120 HV, 344 MPa, and 355 MPa, respectively, after five passes. The HallâPetch effect, dislocation, solid solution, and precipitation strengthening were evaluated to determine the dependence of the yield stress on the ECAP pass number. The results show that the strength effect arises from the subgrain microstructure rather than from the high-angle grain boundaries developed.Peer ReviewedPostprint (published version