Subgrain growth and low angle boundary mobility in aluminium crystals of orientation {110}〈001〉
TL;DR: In this paper, the subgrain growth kinetics of a high purity Al-0.05% Si single-phase aluminium alloy were investigated at room temperature and 350°C.
Abstract: Single crystals of orientation {110}〈001〉 of a high purity Al–0.05% Si single-phase aluminium alloy have been deformed in channel die plane strain compression at room temperature and 350°C. The specimens were annealed at temperatures between 250 and 400°C and detailed measurements have been made of the extensive subgrain growth which occurs in these crystals. It was found that subgrain growth tended to be discontinuous, confirming earlier experimental and theoretical work, and showing that subgrain growth is quite different from normal grain growth. The mean misorientation between subgrains decreased during annealing and this was shown to have a strong effect on the kinetics of subgrain growth. The mobilities of low angle boundaries (2.6°<θ<5.6°) at temperatures between 250 and 400°C were determined from the subgrain growth kinetics and the activation energies for migration found to be consistent with control by lattice diffusion of solute. The boundary mobilities were found to increase rapidly with increasing misorientation and the results have been compared with the predictions of current theories.
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TL;DR: The application of automated electron backscatter diffraction (EBSD) in the scanning electron microscope, to the quantitative analysis of grain and subgrain structures is discussed and compared with conventional methods of quantitative metallography.
Abstract: The application of automated Electron Backscatter Diffraction (EBSD) in the scanning electron microscope, to the quantitative analysis of grain and subgrain structures is discussed and compared with conventional methods of quantitative metallography. It is shown that the technique has reached a state of maturity such that linescans and maps can routinely be obtained and analysed using commercially available equipment and that EBSD in a Field Emission SEM (FEGSEM) allows quantitative analysis of grain/subgrains as small as ∼0.2 μm. EBSD can often give more accurate measurements of grain and subgrain size than conventional imaging methods, often in comparable times. Subgrain/cell measurements may be made more easily than in the TEM although the limited angular resolution of EBSD may be problematic in some cases. Additional information available from EBSD and not from conventional microscopy, gives a new dimension to quantitative metallography. Texture and its correlation with grain or subgrain size, shape and position are readily measured. Boundary misorientations, which are readily obtainable from EBSD, enable the distribution of boundary types to be determined and CSL boundaries can be identified and measured. The spatial distribution of Stored Energy in a sample and the amount of Recrystallization may also be measured by EBSD methods.
943 citations
TL;DR: The absolute grain boundary mobility of 388 nickel grain boundaries was calculated using a synthetic driving force molecular dynamics method; complete results appear in the Supplementary materials as discussed by the authors. But the authors did not consider the effect of boundary mobility on grain boundary roughening.
Abstract: The absolute grain boundary mobility of 388 nickel grain boundaries was calculated using a synthetic driving force molecular dynamics method; complete results appear in the Supplementary materials. Over 25% of the boundaries, including most of the non-Σ3 highest mobility boundaries, moved by a coupled shear mechanism. The range of non-shearing boundary mobilities is from 40 to 400 m/s GPa, except for Σ3 incoherent twins which have mobilities of 200–2000 m/s GPa. Some boundaries, including all the 〈1 1 1〉 twist boundaries, are immobile within the resolution of the simulation. Boundary mobility is not correlated with scalar parameters such as disorientation angle, Σ value, excess volume or boundary energy. Boundaries less than 15° from each other in five-dimensional crystallographic space tend to have similar mobilities. Some boundaries move via a non-activated motion mechanism, which greatly increases low-temperature mobility. Thermal roughening of grain boundaries is widely observed, with estimated roughening temperatures substantially among boundaries.
646 citations
TL;DR: Very-high-rate shear deformation with high strain gradients was applied in the top surface layer of bulk nickel, where a 2D nanometer-scale laminated structure was induced, producing a stronger, more thermally robust nickel microstructure.
Abstract: Heavy plastic deformation may refine grains of metals and make them very strong. But the strain-induced refinement saturates at large strains, forming three-dimensional ultrafine-grained (3D UFG) structures with random orientations. Further refinement of this microstructure is limited because of the enhanced mobility of grain boundaries. Very-high-rate shear deformation with high strain gradients was applied in the top surface layer of bulk nickel, where a 2D nanometer-scale laminated structure was induced. The strongly textured nanolaminated structure (average lamellar thickness of 20 nanometers) with low-angle boundaries among the lamellae is ultrahard and ultrastable: It exhibits a hardness of 6.4 gigapascal--which is higher than any reported hardness of the UFG nickel--and a coarsening temperature of 40 kelvin above that in UFG nickel.
426 citations
TL;DR: In this article, the motion of planar symmetrical and asymmetrical tilt boundaries in high-purity aluminium with -and -tilt axes under the influence of an external mechanical stress field was investigated.
Abstract: We investigated the motion of planar symmetrical and asymmetrical tilt boundaries in high-purity aluminium with - and -tilt axes under the influence of an external mechanical stress field. It was found that the motion of low-angle grain boundaries as well as high-angle grain boundaries can be induced by the imposed external stress. The observed activation enthalpies allow conclusions on the migration mechanism of the grain boundary motion. The motion of planar low- and high-angle grain boundaries under the influence of a mechanical stress field can be attributed to the movement of the grain boundary dislocations which comprise the structure of the boundary. A sharp transition between low-angle grain boundaries and high-angle grain boundaries was observed at 13.6°, which was apparent from a step of the activation enthalpy for the grain boundary motion. For the investigated boundaries the transition angle was independent of tilt axis, impurity content and tilt boundary plane.
230 citations
TL;DR: In this paper, the development of texture and boundary character during annealing, three-dimensional grain crystallography and crystallographically mediated grain boundary properties were incoporated into a finite temperature Monte Carlo model for grain growth.
Abstract: In order to study the development of texture and boundary character during annealing, three-dimensional grain crystallography and crystallographically mediated grain boundary properties were incoporated into a finite temperature Monte Carlo model for grain growth. Randomly textured microstructures evolve normally, with growth exponent n=0.96. While texture remains random, the steady-state boundary misorientation distribution favors low-angle boundaries. To first order, low-angle boundaries increase by lengthening, not by proliferating. In contrast, microstructures with a strong single-component texture develop four-grain junctions and highly curved grain boundaries, which alter evolution. The boundary misorientation distribution narrows and shifts to low angles, and no steady state is observed. The accompanying decrease in mean boundary mobility causes growth to slow, resulting in a growth exponent n=0.62. The dependence of the growth exponent on average boundary mobility may explain experimental observations of exponents less than unity.
215 citations
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07 Nov 1996
TL;DR: In this paper, the authors discuss the extent to which we are able to formulate quantitative, physically-based models which can be applied to metal-forming processes, and the subjects treated in this book are all active research areas and form a major part of at least four regular international conference series.
Abstract: Paperback. The annealing of deformed materials is of both technological importance and scientific interest. The phenomena have been most widely studied in metals, although they occur in all crystalline materials such as the natural deformation of rocks and the processing of technical ceramics. Research is mainly driven by the requirements of industry, and where appropriate, the book discusses the extent to which we are able to formulate quantitative, physically-based models which can be applied to metal-forming processes.The subjects treated in this book are all active research areas, and form a major part of at least four regular international conference series. However, there have only been two monographs published in recent times on the subject of recrystallization, the latest nearly 20 years ago. Since that time, considerable advances have been made, both in our understanding of the subject and in the techniques available to the researcher.The
7,149 citations
TL;DR: In this paper, an analysis of the growth and stability of cellular microstructures, which takes account of the orientation dependence of boundary energies and mobilities, is presented and used to develop a simple unified theory of continuous and discontinuous recovery, recrystallization and grain growth.
Abstract: An analysis of the growth and stability of cellular microstructures, which takes account of the orientation dependence of boundary energies and mobilities, is presented and used to develop a simple unified theory of continuous and discontinuous recovery, recrystallization and grain growth. The analysis shows that low angle subgrain structures are intrinsically very unstable whilst medium to high angle structures may be very stable. The model is used to analyse discontinuous subgrain growth, primary recrystallization, the effects of texture on grain growth and the stability of highly strained metals.
517 citations
TL;DR: A combination of in situ annealing and electron backscattered diffraction in the SEM has been used to determine the mobility of high angle grain boundaries in a deformed single-phase Al-Si alloy as mentioned in this paper.
Abstract: A combination of in situ annealing and electron backscattered diffraction in the SEM has been used to determine the mobility of high angle grain boundaries in a deformed single-phase Al–Si alloy. It is found that the boundary velocity is directly proportional to the driving pressure and that the activation energy for boundary migration over all the conditions investigated is consistent with control by lattice diffusion of the solute. It is confirmed that tilt boundaries of recrystallized grains misoriented by 40±10° about axes within ±10° of 〈111〉 have an increased mobility compared to other high angle boundaries, whereas the mobilities of 40°〈111〉 twist boundaries are similar to those of general high angle boundaries. The mobility maximum for the 40°〈111〉 tilt boundaries is very broad, which is in contrast to the sharp mobility peaks reported for curvature-driven grain growth, and possible reasons for these differences are discussed.
170 citations
TL;DR: In this article, an extended impurity drag theory is presented that takes into account interaction of the adsorbed atoms in the boundary, which predicts a concentration dependence of the activation enthalpy.
Abstract: The influence of impurities on grain boundary mobility in a Σ7 (38.2° ) and in an off-coincidence boundary (40.5° ) was investigated. The grain boundary mobility was found to strongly depend on grain boundary crystallography and material purity. The measured concentration dependence of activation enthalpy and preexponential mobility factor did not comply with predictions of traditional impurity drag theory. An extended impurity drag theory is presented that takes into account interaction of the adsorbed atoms in the boundary. This theory predicts a concentration dependence of the activation enthalpy. For the Σ7 boundary it can explain qualitatively the frequently observed high values of preexponential mobility factor and activation enthalpy. The compensation temperature was found to depend on composition.
136 citations