Navegando por Autor "Pereira, Pedro Henrique Rodrigues"
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Item Influence of strain amplitude on the microstructural evolution and flow properties of copper processed by multidirectional forging.(2020) Flausino, Paula Cibely Alves; Nassif, Maria Elisa Landim; Bubani, Franco de Castro; Pereira, Pedro Henrique Rodrigues; Aguilar, Maria Teresa Paulino de; Cetlin, Paulo RobertoCommercial-purity copper (99.8%) is processed by multidirectional forging (MDF) using strain amplitudes per compression (Δε) of 0.15 and 0.30, leading to accumulated strains (ε) of up to 10.8. It is shown that increasing the accumulated strain causes continuous reactions at the substructural level, involving the progressive evolution of dislocation arrangements toward structures having high misorientation angles. This evolution depends upon the strain amplitude in MDF processing and is characterized by the fragmentation of the original grains due to formation and intersection of micro shear bands (MSBs) assisted by dynamic recovery processes. Higher Δε enhances the “monotonic” character of processing, resulting in a higher fraction of MSBs and band intersections, increased work hardening, flow stresses, and dislocation density, lower cell/subgrain and grain sizes, and faster grain refinement kinetics, compared with MDF under lower Δε. The yield strength of copper, measured along a direction orthogonal to that of the previous compression step, is lower than the flow stress at the end of this compression step, and this behavior becomes more prominent with increasing ε and Δε.Item Mechanical behavior and microstructures of aluminum in the MultiAxial Compression (MAC) with and without specimen re-machining.(2019) Stemler, Pedro Malaquias Araujo; Flausino, Paula Cibely Alves; Pereira, Pedro Henrique Rodrigues; Faria, Cleber Granato de; Almeida, Natanael Geraldo e Silva; Aguilar, Maria Teresa Paulino de; Cetlin, Paulo RobertoSevere Plastic Deformation (SPD) leads to grain refinement and strengthening of metals. The most utilized SPD techniques are Equal Channel Angular Pressing (ECAP), High Pressure Torsion (HPT) and Multi-Axial Compression (MAC). Only MAC allows the determination of the stress–strain curves of the material during processing. Although ECAP and HPT processing has been analyzed in detail, there are few studies of MAC procedures and their consequences. It is shown that only specimens re-machined after each compression lead to adequate MAC stress–strain curves of the material, whose microstructures are not affected by re-machining.Item Microstructural evolution and mechanical behavior of copper processed by low strain amplitude multi-directional forging.(2019) Flausino, Paula Cibely Alves; Nassif, Maria Elisa Landim; Bubani, Franco de Castro; Pereira, Pedro Henrique Rodrigues; Aguilar, Maria Teresa Paulino de; Cetlin, Paulo RobertoExperiments were performed to analyze the microstructural evolution and mechanical behavior of commercial-purity copper (99.8%) processed by up to 48 cycles of multi-directional forging (MDF) using a low strain amplitude of ∼0.075 (total accumulated strain ε ≈ 10.8). Parabolic work-hardening concomitantly with increasing dislocation densities was observed up to ε ≈ 2, followed by a practically constant flow stress due to dynamic recovery. The average grain size was reduced from 30.5 μm in the annealed metal down to 4.1 μm for ε ≈ 7.2; the fraction of sub-micrometric grains reached ∼12% for ε ≈ 10.8. The microstructural changes were attributed to the fragmentation of the original grains by dislocation structures having low misorientation angles which gradually evolved into arrays of high-angle grain boundaries with increasing numbers of MDF cycles. The Cu samples subjected to 48 cycles of MDF displayed limited dynamic recrystallization, exhibiting basically dislocation cells and sub-grains with an average size of ∼0.6 μm. It is demonstrated that low strain amplitude MDF delays the kinetics of grain refinement in copper compared with MDF using higher strain amplitudes.Item Thermal stability of copper processed by multidirectional forging : effect of deformation amplitude and cumulative strain.(2022) Flausino, Paula Cibely Alves; Corrêa, Elaine Carballo Siqueira; Pereira, Pedro Henrique Rodrigues; Aguilar, Maria Teresa Paulino de; Cetlin, Paulo RobertoExperiments were performed in order to evaluate the effect of deformation amplitude (Δε) and cumulative strain (ε) on the thermal stability of Copper 99.8% pure, after processing with 8 and 48 Multidirectional forging (MDF) cycles at room temperature with Δε ≈ 0.075 (MDF0.075) or 2 and 12 MDF cycles with Δε ≈ 0.30 (MDF0.30), leading to cumulative deformations of ε ≈ 1.8 and 10.8. The microstructural stability at elevated temperatures was evaluated through Differential Scanning Calorimetry (DSC) and heat treatments, combined with Vickers microhardness measurements and Electron Backscattered Diffraction (EBSD). Further analyses were carried out through thermodynamic considerations about the stored energy and driving pressures for boundary migration. The results showed that the thermal stability associated with static recrystallization decreases as ε and Δε in MDF increase, due to the presence of finer grain structures and higher dislocation density in the as-deformed material. In addition, the MDF-processed specimens deformed with high ε and Δε exhibited finer recrystallized grains than those processed with low ε and Δε as a result of their increased number of nucleation sites. Thermal stability increases in the following order: 12C-MDF0.30, 2C-MDF0.30, 48C-MDF0.075 and 8C-MDF0.075.