Papers by Keyword: Geometric Dynamic Recrystallization

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Authors: Jian Shen, Yong Heng ShangGuan, Xiao Dong Yan
Abstract: Evolution of flow stress and microstructures of an Al-Zn-Mg series alloy during deformation at elevated temperatures and large ranges of strain rates have been investigated by isothermal compression testing on Gleeble 1500 thermomechanical simulator. The results showed that the flow stress exhibited a characteristic of peak stress followed by smoothing out in the imposed strain rate and temperature ranges. The hot deformation of the alloy is a thermally activated process, which is controlled by rate-controlling mechanisms of dislocation generation and dislocation annihilation. The flow stress decreases with the increase of true strain at higher temperature and lower strain rate, indicating that dynamic softening dominates instead of strain hardening during hot deformation of the alloy. Microstructure observation revealed that typical subgrain cluster structures obviously developed in the original elongated grains of the alloy during hot deformation. The subgrain size of the alloy increased with deformation temperature and downturn of strain rate, where the Zener-Hollomon parameter increased. Fine equiaxed recrystallized grains with large-angle grain boundaries developed significantly in the alloy during hot compression at low Z values, implying activation of dynamic recrystallization.
Authors: Wolfgang Blum, Q.S. Zhu, R. Merkel, H.J. McQueen
Authors: M.E. Kassner, H.J. McQueen, E. Evangelista
Authors: S.R. Barrabes, M.E. Kassner, Maria Teresa Pérez-Prado, E. Evangelista
Abstract: The micron-size grain refinement of pure a-zirconium obtained with elevated temperature tensile deformation was investigated. The development of low-misorientation subboundaries caused the serration of the original grain boundaries at low strains. The final microstructure (e.g. strains > 3) was predominantly composed of fine, equiaxed “crystallites” with ⅔ of the boundaries being of very low misorientations (< 3°) and the remaining ⅓ being high angle boundaries (θ > 8°, and typically 25-35°). Discontinuous dynamic recrystallization was excluded as a possible mechanism due to the absence of newly formed grain nuclei. The bimodal distribution of the crystallite or (sub)grain boundary misorientations is inconsistent with the occurrence of continuous dynamic recrystallization and rotational recrystallization. The continual thinning of the original grains, the serration of the high angle boundaries, the bimodal misorientation distribution of misorientations, ⅔ of boundaries of very low misorientations at high strains all strongly suggest geometric dynamic recrystallization and dynamic recovery as the grain refinement and restoration mechanisms.
Authors: G. Avramovic-Cingara, H.J. McQueen
Abstract: Specimens of commercial purity aluminum were subjected to a strain path change test during high temperature deformation. Specimens were deformed at 4000 C and strain rate of 0.1 s-1 up to various strains of 0.2, 0.5, and 1. Then in a strain path change test, specimens were first deformed to a strain of 0.5, and subsequently deformed to strains of 0.2 and 0. In order to further the understanding of the deformation mechanisms in aluminum, the subgrain sizes and misorientations were characterized in detail by comparative studies using optical microscopy in polarized light (POM), orientation imaging microscopy (OIM/SEM) and transmission electron microscopy (TEM). The analysis revealed that while subgrain size is relatively insensitive to strain, overall misorientations increased with increasing strain. These analyses confirmed a strong bimodal distribution of boundaries during deformation coupled with a low fraction of medium angle boundaries. The results contribute to the understanding that dynamic recovery in aluminum maintains subboundaries with low misorientation but as grains elongate and more subgrain become adjacent to grain boundaries the fraction of high angle boundaries rises.
Authors: Rampada Manna, N.K. Mukhopadhyay, G.V.S. Sastry
Abstract: Grain refinement of aluminum deformed by equal channel angular pressing is strongly dependent on the amount of strain. The refinement process at low to high strain level involves elongation of the existing grains by shear deformation, their subdivision into bands and subgrain formation within bands, intersection of the bands during subsequent passes and finally conversion of the subgrains to grains by continuous dynamic recrystallization process. At room temperature the conversion of subgrains to grains takes place by progressive lattice rotation.
Authors: Pavel Sherstnev, Adrian Zamani
Abstract: Under certain conditions of extrusion temperature and strain rate Al-Mg-Si alloys produce coarse recrystallized grains at and near the surface. Current FEM models are able to analyze grain size evolution for extruded profiles, but cannot predict the coarse recrystallized grains near the surface. A new model using DEFORM 2D and local state variables such as strain, strain rate and temperature is compared with Al-Mg-Si rods extruded at 440°C and 500°C for two extremes of strain rate. The model is found to be sensitive to the processing conditions and to accurately predict the recrystallized grain size and fraction.
Authors: Jian Shen, Y.Q. Song, Shui Sheng Xie, Günter Gottstein
Authors: S. Gourdet, E.V. Konopleva, H.J. McQueen, Frank Montheillet
Authors: Ali Gholinia, John F. Humphreys, Philip B. Prangnell
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