Navegando por Palavras-chave "severe plastic deformation"

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    Dissolution of the second phase particles in the course of the equal channel angular pressing of diluted Cu-Cr-Zr alloy
    (Russian Acad Sciences, Inst Metals Superplasticity Problems, 2018) Faizov, I. A.; Mulyukov, R. R.; Aksenov, D. A.; Faizova, S. N.; Zemlyakova, N. V.; Cardoso, K. R. [UNIFESP]; Zeng, Yu.
    Changes of properties and the second phase particles' distribution in diluted CuCrZr alloy in the course of equal channel angular pressing (ECAP) and post-deformation annealing are investigated. To decrease the concentration of alloying elements dissolved in the copper matrix, samples of the alloy were thermally aged prior to the ECAP. Temperature of annealing, 450 degrees C, was the same as the one used for the subsequent post-deformation aging, and the time of annealing was long enough to reach a practically equilibrium state. The enthalpy release rate curve of the ECAP-processed sample, unlike the one for the initial state exhibits an exopeak in the temperature range 440..470 degrees C, which is typical for breakdown of the solid solution in alloys of this system. The post-deformation aging causes a significant increase in the tensile strength as compared to the value immediately after the ECAP. This increase can be related only to the dispersion strengthening that is confirmed by the observation of higher density of particles after the aging. These facts unambiguously indicate that the solid solution at the aging temperature is supersaturated, i.e. its concentration increased in the course of the ECAP due to the deformation-induced dissolution of the second phases. This conclusion agrees with the behavior of the electrical conductivity that noticeably decreases upon the ECAP and recovers its initial value after the aging. As the density of structural defects is significantly different in the initial and final states, the observed decrease can be related only to the lattice distortion due to dissolved foreign atoms.
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    Microstructure evolution of AA7050 Al alloy during Equal-Channel Angular Pressing
    (ABM, ABC, ABPol, 2012-10-01) Cardoso, Kátia Regina [UNIFESP]; Travessa, Dilermando Nagle [UNIFESP]; Jorge Junior, Alberto Moreira; Botta, Walter José; Universidade Federal de São Paulo (UNIFESP); UFSCar Departamento de Engenharia de Materiais
    High strength AA7050 aluminum alloy was processed by ECAP through route A in the T7451 condition. Samples were processed at 423 K, with 1 and 3 passes. The resulting microstructure was evaluated by optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The phases were identified by X-ray diffraction (XRD) using monochromatic Cu Kα radiation. Rockwell B hardness and tensile tests were performed for assessment of mechanical properties. The microstructure was refined by the formation of deformation bands, with dislocation cells and elongated subgrains, with an average width of 240 nm, inside these bands. The number of deformation bands increased with the number of passes. A reduction of precipitates size was observed with increase in the number of passes, when compared to initial condition, probably resulting from particle fragmentation during ECAP. After three passes the precipitates tend to a more equiaxed morphology and have sizes smaller than 10 nm. Phases Η' and Η coexist in the microstructure, but Η is the dominant phase, mainly after three passes. The hardness of alloy after the first pass of ECAP is almost equal to the initial condition. After three passes the hardness showed a slight reduction which must be result from recovery process. There was a slight improvement in the yield strength and elongation after one pass, when compared to the initial T7451 condition. The improvement in the ultimate tensile strength was less significant.