Papers by Author: I. Mazurina

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Authors: I. Mazurina, Oleg Sitdikov, Rustam Kaibyshev, Hiromi Miura, Taku Sakai
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Authors: Rustam Kaibyshev, I. Mazurina, Oleg Sitdikov
Abstract: The mechanism of new grain evolution during equal channel angular extrusion (ECAE) up to a total strain of ~12 in an Al-Cu-Mn-Zr alloy at a temperature of 475oC (0.75Tm) was examined. It was shown that the new grains with an average size of about 15 µm result from a specific process of geometric dynamic recrystallization (GRX) which can be considered as a type of continuous dynamic recrystallization (CDRX). This process involves three elementary mechanisms. At moderate strains, extensive elongation of initial grains takes place; old grain boundaries become progressively serrated. Upon further ECAE processing, transverse low-angle boundaries (LAB) with misorientation ranging from 5 to 15o are evolved between grain boundary irregularities subdividing the initial elongated grains on crystallites with essentially equiaxed shape. The misorientation of these transverse subboundaries rapidly increases with increasing strain, resulting in the formation of true recrystallized grains outlined by high-angle boundaries from all sides. In the same time, the average misorientation of deformation-induced boundaries remains essentially unchanged during ECAE. It is caused by the fact that the evolution of LABs with misorientation less than 4o occurs continuously during severe plastic deformation. The mechanism maintaining the stability of the transverse subboundaries that is a prerequisite condition for their further transformation into highangle boundaries (HABs) is discussed.
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Authors: Rustam Kaibyshev, I. Mazurina
Abstract: The mechanisms of grain refinement during severe plastic deformation have been studied, by comparing the microstructure evolution in an AA2219 aluminium alloy, containing Al3Zr nanoscale particles, with that in a dilute Al-3%Cu alloy deformed identically by equalchannel angular extrusion (ECAE) at 250oC to a maximum strain of ~12. Transmission electron microscopy (TEM) was used on the AA2219 alloy to reveal the misorientations of deformationinduced boundaries. Microstructural evolution in the Al-3%Cu alloy was studied by electron-back scattering diffraction (EBSD) orientation mapping. It was shown that the mechanism of grain refinement in the AA2219 alloy is continuous dynamic recrystallization (CDRX) consisting of two main elementary processes. In the initial stages of plastic deformation, the formation of threedimensional arrays of low-angle boundaries (LABs) takes place. Further strain results in increasing misorientation of these boundaries providing their gradual transformation into high-angle boundaries (HABs). A fully recrystallized structure with an average grain size of ~0.9 µm is evolved after a total strain of ~12. In the dilute Al-Cu alloy the evolution of ultrafine grains with an average size of ~6 µm is attributed to the formation of deformation bands outlined by HABs and extended medium to high-angle boundaries at moderate strains. The subdivision of these deformation bands into fine grains rarely occurs through the mechanism of geometric recrystallization (GRX). In this alloy the main contribution in the grain refinement gives CDRX occurring within fibrous structural features. At e~12, a partially recrystallized structure is formed in the Al-3%Cu alloy.
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Authors: I. Mazurina, Alexandre Goloborodko, Rustam Kaibyshev, Hiromi Miura, Taku Sakai
Abstract: Microstructural evolution during equal channel angular extrusion (ECAE) was investigated in a coarse-grained dilute aluminum alloy, Al-3%Cu, at a temperature of 250oC. Scanning electron microscopy (SEM) with electron back scattering diffraction (EBSD) and optical metallography (OM) was used to reveal the structural changes in the alloy deformed up to a strain of ε=12. The microstructural evolution at initial and moderate stages of deformation is characterized by the formation of low angle boundaries and deformation bands with moderate misorientations in grain interiors. With further deformation the number and the misorientation of the deformation bands increase, finally leading to the subdivision of original grains by these bands and then the development of fine grains with an average size of about 6 μm at ε=12. The evolution of deformation bands in initial grain interiors and their role on new grain formation are discussed in detail.
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