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Plastic deformation of ARMCO iron processed by ECAP up to a maximum equivalent strain of sixteen (i.e., 1, 4, 8, and 16 ECAP passes) following route Bc was investigated by analyzing its microstructure and the stress-strain curves obtained after tensile tests at different levels of deformation. Three values of deformation (two in the plastic region taking into account the modified Crussard-Jaoul analysis and one after failure) were considered. Fractions of LAGB and HAGB, grain size and grain aspect ratio were calculated and compared for the different ECAP passes and tensile deformation levels. The dislocation density evolution calculated by the Bergström model for both the tensile curves and the ECAP curve showed a higher increase in the amount of dislocations during the initial stages of deformation than at higher values of deformation due to higher probabilities of dislocations annihilation. The strain hardening exponents calculated via the Bergström model for each ECAP pass shows that there is a continuous decrease in the strain hardening capacity until the eighth pass where a small increase with a subsequent stabilization was found. The dislocation densities calculated by the Estrin model presented a good correlation with values reported in bibliography for iron especially with those calculated by X-ray diffraction.This latter model predicted well the strain hardening evolution for stages 2 III, IV and V for ARMCO iron processed by ECAP, where the main increments in hardening for stages IV and V were coming from the cell interiors.

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The thermal stability of ARMCO iron processed by equal-channel angular pressing (ECAP) up to a true strain of sixteen was investigated by differential scanning calorimetry (DSC). Particularly, the analysis was focused on deriving the recrystallization behavior (onset, peak and offset temperatures) at three different heating rates (10, 20 and 40ºC/minute). Additionally, the stored and activation energies were calculated. As well, the microstructure and the tensile response were evaluated at different numbers of passes before and after annealing heat treatment to assess any significant grain growth and its influence on the material ductility. The different energy contributions (dislocations, grain boundaries, and vacancies) were calculated, being verified that the main contribution came from vacancies.

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The high-cycle fatigue behavior of ARMCO iron severely deformed by Equal Channel Angular Pressing (ECAP) at room temperature through route Bc until 8 passes, with an average grain size of ~365 nm, was studied and compared with the same material in the annealed state with an average grain size of ~72 µm. The fatigue limit of the 8 passes ECAPed sample increased with respect to the annealed material by more than 250% rising from 274 MPa to 717 MPa. Striations and dimpled relief were observed on the fracture surfaces of the fatigued ultrafine and coarse grain fatigue samples. The microstructure was characterized by Electron Backscattered Diffraction (EBSD) before and after the fatigue tests and it was observed in both samples an increment in the fraction of Low Angle Grain Boundaries (LAGB) at high number of cycles to failure. A texture analysis for the materials after the fatigue failure was done. This study shown a preferential orientation towards the ¿ fiber for both conditions.Peer ReviewedPostprint (author's final draft

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We study the deformation inducing heterogeneity in an Aluminum alloy 6063-T6 in the form of a sheet processed at room temperature by Equal Channel Angular Sheet Extrusion (ECASE) up to a maximum equivalent strain of 1.86 following route C. The through thickness strain distribution showed higher strains in the edge vicinities than in the sheet core. The texture was heterogeneous between the edges and the sheet core with a strong Cube component in the initial deformation stages, and a rolling texture with the S component in the sheet edges. Different microstructural characteristic, like grain size, average misorientation and fraction of High Angle Grain Boundaries (HAGB) decreased by increasing the deformation. The Geometrically Necessary Dislocation (GND) calculations corroborated the existence of a heterogeneous microstructure along the sheet thickness, giving rise to gradients of plastic deformation which allowed to obtain a good strength-ductility relationship. It was demonstrated that ECASE process was a good alternative to produce heterogeneous microstructures. The material heterogeneity was found not to be randomly distributed across the sheet thickness but rather showing higher dislocation concentration and bigger grain size reductions in the edge's vicinities than in its middle zone.