Papers by Keyword: Dynamic Grain Growth

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Authors: Oleg V. Rofman, Pete S. Bate
Abstract: The effect of deformation on the microstructure of a Al-4wt.%Cu alloy has been investigated. Evaluation of the microstructural changes was made by comparing results after both static annealing and tensile testing (deformed and non-deformed regions) at 450 °C. Uniaxial perturbed-rate tests showed that the Al-4wt.%Cu has a low value of the strain rate sensitivity index (m ~ 0.22) and cannot be considered as a superplastic material. It was found that in the deformed regions, specimens showed a significant increase in the grain and particle size. These changes were accompanied by an increase in the aspect ratio of the matrix grains. Tensile tests carried out at constant strain rates and stopped at intermediate strains helped to estimate the rate of the grain and particle growth and the contribution of deformation to it. To examine in detail the mechanism of the particle coarsening during deformation, additional tensile tests were made using the Al-4wt.%Cu alloy annealed at temperature conditions leading to abnormal grain size. Results of these tests also showed strain-induced particle coarsening, so that dynamic particle coarsening was not simply caused by boundary migration effects.
Authors: K.B. Hyde, Pete S. Bate
Authors: Pete S. Bate, K.B. Hyde, S.A. Court, John F. Humphreys
Authors: Keijiro Hiraga, Byung Nam Kim, Koji Morita, Yoshio Sakka
Authors: A. Kellermann Slotemaker, J.H.P. de Bresser, C.J. Spiers, M.R. Drury
Abstract: Microstructures provide the crucial link between solid state flow of rock materials in the laboratory and large-scale tectonic processes in nature. In this context, microstructural evolution of olivine aggregates is of particular importance, since this material controls the flow of the Earth’s upper mantle and affects the dynamics of the outer Earth. From previous work it has become apparent that if olivine rocks are plastically deformed to high strain, substantial weakening may occur before steady state mechanical behaviour is approached. This weakening appears directly related to progressive modification of the grain size distribution through competing effects of dynamic recrystallization and syn-deformational grain growth. However, most of our understanding of these processes in olivine comes from tests on coarse-grained materials that show grain size reduction through dynamic recrystallization. In the present study we focused on fine-grained (~1 µm) olivine aggregates (i.e., forsterite/Mg2SiO4), containing ~0.5 wt% water and 10 vol% enstatite (MgSiO3), Samples were axially compressed to varying strains up to a maximum of ~45%, at 600 MPa confining pressure and a temperature of 950°C. Microstructures were characterized by analyzing full grain size distributions and textures using SEM/EBSD. We observed syndeformational grain growth rather than grain size reduction, and relate this to strain hardening seen in the stress-strain curves.
Authors: H. Jazaeri, John F. Humphreys, Pete S. Bate
Abstract: Al-0.1Mg with a 3μm grain size was deformed in channel die plane strain compression at temperatures up to 200oC. It was found that the reduction in grain thickness was significantly less than that predicted from geometric considerations, and at larger strains, a minimum high angle grain spacing, which was equal to the crystallite size was achieved. The velocity of the high angle boundaries during this process is very many orders of magnitude larger than that predicted for curvature driven grain growth, and some possible explanations for this are discussed.
Authors: Kasra Sotoudeh, Pete S. Bate, John F. Humphreys
Abstract: The effect of copper content on dynamic grain growth in Al-Cu-Zr system was investigated by studying the microstructural development and texture evolution during uniaxial tensile deformation of Al-2wt%Cu-0.3wt.%Zr and Al-4wt%Cu-0.4wt.%Zr alloys at 450°C with a strain rate of 10-3s-1, with a similar initial microstructure in both materials. The initial microstructure consisted of layers of different orientations, the layers being separated by high-angle grain boundaries with low-angle boundaries separating grains within the layers. The initial grain spacing was about 5m and the texture was typical of rolled aluminium alloys. The 4wt.%Cu alloy gave a higher strain rate sensitivity index, m, and a greater ductility compared to the low copper content alloy. An increase in grain size occurred in both materials due to deformation, but this dynamic grain growth (DGG) was much greater in the material with the higher copper content. This was associated with a more rapid conversion of low-angle boundaries to high angle ones in the 4wt%Cu material which is consistent with changes in crystallographic texture occurring during deformation.
Authors: B. Zhang, Pete S. Bate, Norman Ridley
Abstract: Dynamic grain growth in superplastic AA5083 deformed at constant strain rates and varying strain rates has been studied. It has been found that the strain rate history has a significant influence on the grain growth behaviour. It is proposed that differences in mechanical behaviour of AA5083 for the strain rate conditions examined can be attributed to differences in the grain growth behaviour. The influence of dynamic grain growth on the superplastic behaviour of AA5083 is discussed.
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