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The present laboratory diffraction contrast tomography suffers from poor spatial resolution – only grains larger than 40 µm can be reliably imaged. In this work, it is shown how this serious limitation can be lifted and the spatial resolution improved significantly., Laboratory diffraction contrast tomography (LabDCT) is a novel technique for non-destructive imaging of the grain structure within polycrystalline samples. To further broaden the use of this technique to a wider range of materials, both the spatial resolution and detection limit achieved in the commonly used Laue focusing geometry have to be improved. In this work, the possibility of improving both grain indexing and shape reconstruction was investigated by increasing the sample-to-detector distance to facilitate geometrical magnification of diffraction spots in the LabDCT projections. LabDCT grain reconstructions of a fully recrystallized iron sample, obtained in the conventional Laue focusing geometry and in a magnified geometry, are compared to one characterized by synchrotron X-ray diffraction contrast tomography, with the latter serving as the ground truth. It is shown that grain indexing can be significantly improved in the magnified geometry. It is also found that the magnified geometry improves the spatial resolution and the accuracy of the reconstructed grain shapes. The improvement is shown to be more evident for grains smaller than 40 µm than for larger grains. The underlying reasons are clarified by comparing spot features for different LabDCT datasets using a forward simulation tool.

A deep learning neural network has been developed to efficiently and accurately clean the background noise in experimental lab-based X-ray diffraction images. A better spot segmentation is obtained and thus grain mapping in 3D is improved compared with the conventional method., Laboratory X-ray diffraction contrast tomography (LabDCT) is a novel imaging technique for non-destructive 3D characterization of grain structures. An accurate grain reconstruction critically relies on precise segmentation of diffraction spots in the LabDCT images. The conventional method utilizing various filters generally satisfies segmentation of sharp spots in the images, thereby serving as a standard routine, but it also very often leads to over or under segmentation of spots, especially those with low signal-to-noise ratios and/or small sizes. The standard routine also requires a fine tuning of the filtering parameters. To overcome these challenges, a deep learning neural network is presented to efficiently and accurately clean the background noise, thereby easing the spot segmentation. The deep learning network is first trained with input images, synthesized using a forward simulation model for LabDCT in combination with a generic approach to extract features of experimental backgrounds. Then, the network is applied to remove the background noise from experimental images measured under different geometrical conditions for different samples. Comparisons of both processed images and grain reconstructions show that the deep learning method outperforms the standard routine, demonstrating significantly better grain mapping.

In this work, it is investigated how grain boundaries influence the local strain determination by the microstructural feature tracking (MFT) algorithm. In this method, tetrahedra are used as the strain calculation unit. We apply the MFT processing procedure on data obtained by a crystal plasticity finite element modeling (CPFEM) simulation to explore the uncertainties in the calculated strains caused by grain boundaries. Effects of tetrahedron types and radius ratios are discussed.

Nucleation of recrystallization at large second phase particles during annealing is essential in many industrially relevant aluminum alloys. To adequately quantify the spatial distribution of such particles and their impact on nucleation in bulk materials, 3D investigations are needed. This study presents a multimodal characterization method to investigate particle stimulated nucleation in a heavily deformed AA5182 alloy. To map the spatial distribution of large second phase particles, conventional laboratory absorption contrast X-ray tomography is used, while the recrystallization nuclei are revealed by Laue micro-diffraction using synchrotron X-rays. The registration of data obtained by the two different non-destructive high-resolution experimental techniques is described. Finally, some preliminary results are presented.

The penetration behavior of liquid gallium in aluminum is characterized using laboratory X-ray attenuation tomography and related to grain boundary properties obtained from the 3D grain map reconstructed by laboratory diffraction contrast tomography (LabDCT). The data is unique because more than 100 grain boundaries are analyzed. It is suggested that it is the grain boundary energy which determines if a boundary is wetted or not: low energy boundaries are much more resistant to liquid gallium than higher energy ones. The potentials of using laboratory diffraction contract tomography for statistical studies of grain boundaries are thereby demonstrated.

The recovery dynamics of 498 individual subgrains within the non-recrystallized matrix of a 50% recrystallized aluminum sample is studied using high resolution X-ray diffraction at a synchrotron source. The subgrains’ change in size, orientation, axial strain and internal disorder are monitored as functions of temperature. The subgrains are surprisingly active, and the individual subgrains exhibit markedly different growth kinetics. Contradictory to common knowledge we find that the individual subgrains’ sizes change significantly even though the average size remain constant. Furthermore we observe no correlation between subgrain size and growth rate. An analysis of the volume changes of the individual subgrains indicates a broad spectrum of critical temperatures above which the subgrains grow or shrink. Possible mechanisms are discussed and related to relaxation of local stresses.

A flexible and standalone forward simulation model has been developed to compute the diffraction projections for laboratory diffraction contrast tomography (LabDCT). The outputs are expected to be of great value for all present users of LabDCT as well as interested new users., Laboratory X-ray diffraction contrast tomography (LabDCT) has recently been developed as a powerful technique for non-destructive mapping of grain microstructures in bulk materials. As the grain reconstruction relies on segmentation of diffraction spots, it is essential to understand the physics of the diffraction process and resolve all the spot features in detail. To this aim, a flexible and standalone forward simulation model has been developed to compute the diffraction projections from polycrystalline samples with any crystal structure. The accuracy of the forward simulation model is demonstrated by good agreements in grain orientations, boundary positions and shapes between a virtual input structure and that reconstructed based on the forward simulated diffraction projections of the input structure. Further experimental verification is made by comparisons of diffraction spots between simulations and experiments for a partially recrystallized Al sample, where a satisfactory agreement is found for the spot positions, sizes and intensities. Finally, applications of this model to analyze specific spot features are presented.

Three-dimensional orientation mapping of samples of aluminum prepared by spark plasma sintering (SPS) with average grain sizes of 5 μm and 1 μm has been carried out using high-brightness synchrotron radiation, from which the geometrically necessary dislocation (GND) density has been determined. The low average measured GND density values confirm that the SPS process can be used to produce samples containing grains with dislocation density similar to that of fully recrystallized coarse-grained samples. Values of GND density are also compared to those obtained from electron back-scatter diffraction studies on the same material, highlighting the significantly higher angular resolution of the synchrotron data. For the 5 μm grain-size sample the measured GND density can account for a large fraction of the previously observed positive Hall-Petch deviation of this material. For the 1 μm grain-size sample, however, the GND-based strengthening contribution is much smaller than the reported positive Hall-Petch deviation, such that the additional strength may be reliably associated with dislocation source-limited strengthening.

In this paper, we discuss the impact that non-destructive 3D (x,y,z) and 4D (x,y,z,time) X-ray experimental methods have had on the understanding of recrystallization of deformed metals. Well-planned experiments on nucleation and grain boundary migration are reviewed with focus on information gained, which could not have been obtained by traditional 2D or destructive 3D methods. It has also been found that the 3D/4D X-ray measurements sometimes happen to reveal phenomena, which were not expected and therefore not planned to investigate. Examples of this are also reviewed here. Finally, the implications of the new findings for modelling of recrystallization are discussed, key experiments for the future are suggested and the needs for technique advancements are summarized, all seen from the recrystallization perspective.

Switches and crossings (S&Cs) in rail networks suffer from damage and deformation due to severe loading of their complex geometric shapes. This article presents a comparative study of the cyclic deformation characteristics and fatigue behavior of two typical crossing materials, namely head-hardened pearlitic steel and Hadfield manganese steel, as well as the associated microstructural changes. Both uniaxial and biaxial loadings (proportional and non-proportional) are studied. The pearlitic steel endured more cycles to failure for a given strain amplitude compared to the manganese steel. The cyclic response of manganese steel shows significant hardening whereas softening was observed for the pearlitic steel except under biaxial non-proportional loading. The microstructures developed in the two types of steels after deformation are characterized by optical (OM) and transmission electron microscopy (TEM). TEM micrographs reveal that the deformed microstructure of the pearlitic steel consists of threading dislocations and dislocation tangles in the ferrite lamellae. The microstructures in the manganese steel after the different loadings are composed of dislocation cells with dislocation tangles inside, intersected by straight stacking fault lamellae. The observed microstructures are related to the results of the mechanical test, and the suitability of the steels for use in S&Cs is discussed.

We present direct evidence of a network of well-defined ultra-low-angle boundaries in bulk recrystallizing grains of 99.5% pure aluminium (AA1050) by means of a new, three-dimensional X-ray mapping technique; dark-field X-ray microscopy. These boundaries separate lattice orientation differences on the order of 0.05° and thus subdivide the recrystallizing grain into 2–7 μm wide domains. During further annealing the orientation differences decrease and the overall structure become more uniform while the network remains. It is observed that the morphology of the grain boundaries surrounding the recrystallizing grains relate to the intragranular network and effects hereof on the boundary migration is discussed.

The roughness of grain boundaries in partly recrystallized microstructures has been quantified. Effects of material and processing parameters on the roughening behavior have been statistically investigated. Parameters are sample purity, deformation strain and boundary migration direction in two cold rolled aluminum samples. The results show that particle pinning is not the main reason accounting for recrystallization boundary roughness in the present samples. The roughness is however shown to relate to the deformation microstructure and possible effects of migration rate are discussed.

The volumetric growth rate of individual grains has been found to be directly proportional to the individual grain volume V as dV/dt = β(Vo -V). This simple result is explained through the DeHoff relationship dV/dt = −kMs between growth rate and the integral mean curvature of individual grains, M s , combined with the experimentally observed relationship between M s and grain volume, M s = α(Vo -V). These relationships have now been observed consistently in both 3D grain growth simulations and experiments. This paper describes the relationships among these kinetic and geometric grain characteristics that provide this simple description of 3D grain growth.

The annealing kinetics of two aluminum alloys AA5xxx is investigated. The volume fraction of recrystallized material, Vv, is determined for a series of partly recrystallized samples both by hardness measurements and by electron back scattering diffraction (EBSD). Because of extended recovery overlapping with recrystallization, in particular in AA5182, it is not straightforward to estimate Vv from the hardness measurements. Two methods are suggested: one relying solely on the hardness data, and one in which EBSD data are used to estimate the hardness at the onset of recrystallization. Effects of the choice of method and of parameters on the resulting annealing kinetics are analysed, and the potential and limitations of the two methods are discussed.

The microstructure and residual elastic strain at graphite nodules (GNs) in ductile cast iron produced using either a fast or slow cooling rate have been characterized using synchrotron 3D X-ray Laue microdiffraction. The results show that thermal stress is introduced during cooling and that part of this stress is relaxed by plastic deformation of the polycrystalline ferrite matrix. It is found that the plastic deformation is accommodated by the formation of dislocations and dislocation boundaries, which are organized in a cell structure. The dislocation density quantified based on the microstructure is most pronounced at the GN/matrix interface around small GNs in the fast cooled sample. Residual elastic strain is also present, which is mainly compressive with a maximum of 6.0–9.9 × 10−4 near the GNs. Gradients of plastic deformation and elastic strain field around the GNs are observed. The results document for the first time that both the elastic strain field and the plastic strain field averaged over the grains around the GNs is approximately scaling with GN size and not affected by the cooling rate. The experimental data are compared with simulations by a finite element method, and agreement and disagreement are discussed in detail.

Lab-based diffraction contrast tomography (LabDCT) has recently enabled nondestructive 3D characterization of the crystallographic orientations and grain morphologies in bulk materials. Despite the wide accessibility and availability of lab-based X-rays, the current spatial resolution of LabDCT is only about 20 μm and has to be improved to make this technique a more versatile tool. Conventional LabDCT takes advantage of the Laue focusing effect, i.e. the diffracted beam from a sample illuminated by an incoming polychromatic beam, is focused when the source and the detector are symmetrically positioned. In this study we have investigated the possibility of increasing the spatial resolution of LabDCT by placing the detector at a distance beyond that required for Laue focusing. We first developed a forward projection simulation tool to elucidate the effects of placing the detector at a larger distance. Next, we performed LabDCT measurements on a partially recrystallized pure aluminum sample at different sample-to-detector distances. The results show that the diffraction spots can be magnified by a factor of about three compared to the current LabDCT setup. The benefits and limitations resulting from increasing the sample-to-detector distance are discussed.

The migration of recrystallization boundaries into spatially varying deformation energy fields are simulated based on a two-dimensional phase-field model. The energy fields are chosen as idealized versions of deformation microstructures subdivided by two sets of intersecting geometrically necessary dislocation boundaries (GNBs), and effects of the sharpness of the GNBs are investigated. The simulations show that the shape of the recrystallizing grain as well as the recrystallization kinetics are considerably affected by the wall characteristics of the GNBs. Recrystallization occurs faster in the deformed matrix with "sharper" walls. The simulation results highlight the importance of the deformation microstructure characteristics on the recrystallization kinetics, and as the deformation microstructures depend on the initial grain orientations, the results also indicate tight relations between initial, deformation and recrystallization textures. ispartof: IOP Conference Series : Materials Science and Engineering vol:1121 status: published

Summary A method is presented, which allows quantification of the roughness of nonplanar boundaries of objects for which the neutral plane is not known. The method provides quantitative descriptions of both the local and global characteristics. How the method can be used to estimate the sizes of rough features and local curvatures is also presented. The potential of the method is illustrated by quantification of the roughness of two recrystallization boundaries in a pure Al specimen characterized by scanning electron microscopy.

Pure tungsten is considered as armor material for the most critical parts of fusion reactors (i.e. the divertor and the first wall), among other reasons due to its high melting point (3422 °C) and recrystallization temperature. The thermal stability of a pure tungsten plate warm-rolled to a high plastic strain by 90% thickness reduction was investigated by isothermal annealing for up to 190 h in the temperature range between 1100 °C and 1250 °C. Vickers hardness testing allowed tracking the changes in mechanical properties caused by recovery and recrystallization. The hardness evolution could be rationalized in terms of a logarithmic recovery kinetics and a Johnson–Mehl–Avrami–Kolmogorov recrystallization kinetics accounting for an incubation time of recrystallization. The observed time spans for recrystallization and the corresponding recrystallization activation energy for this highly deformed plate suggest that large plastic deformations (e.g. applied during shaping) are only suitable to produce tungsten components to be used at relatively low temperatures (up to 900 °C for a 2 years lifespan). Higher operation temperatures will lead to fast degradation of the microstructure during operation.

This work revisits the classical subject of recrystallization of cold-rolled copper. Two characterization techniques are combined: three-dimensional X-ray diffraction using synchrotron X-rays, which is used to measure the growth kinetics of individual grains in situ, and electron backscatter diffraction, which is used for statistical analysis of the microstructural evolution. As the most striking result, the strong cube texture after recrystallization is found to be related to a few super large cube grains, which were named supercube grains. These few supercube grains become large due to higher growth rates. However, most other cube grains do not grow preferentially. Because of the few supercube grains, the grain size distribution after recrystallization is broad. Reasons for the higher growth rates of supercube grains are discussed, and are related to the local deformed microstructure.

How boundaries surrounding recrystallization grains migrate through the 3D network of dislocation boundaries in deformed crystalline materials is unknown and critical for the resulting recrystallized crystalline materials. Using X-ray Laue diffraction microscopy, we show for the first time the migration pattern of a typical recrystallization boundary through a well-characterized deformation matrix. The data provide a unique possibility to investigate effects of both boundary misorientation and plane normal on the migration, information which cannot be accessed with any other techniques. The results show that neither of these two parameters can explain the observed migration behavior. Instead we suggest that the subdivision of the deformed microstructure ahead of the boundary plays the dominant role. The present experimental observations challenge the assumptions of existing recrystallization theories, and set the stage for determination of mobilities of recrystallization boundaries.

Pure tungsten is a potential candidate material for the plasma-facing first wall and the divertor of fusion reactors. Both parts have to withstand high temperatures during service. This will alter the microstructure of the material by recovery, recrystallization and grain growth and will cause degradation in material properties as a loss in mechanical strength and embrittlement. The thermal stability of a pure tungsten plate warm-rolled to 67% thickness reduction was investigated by long-term isothermal annealing in the temperature range between 1150 °C and 1350 °C up to 2200 h. Changes in the mechanical properties during annealing are quantified by Vickers hardness measurements. They are described concisely by classical kinetic models for recovery and recrystallization. The observed time spans for recrystallization and the obtained value for the activation energy of the recrystallization process indicate a sufficient thermal stability of the tungsten plate during operation below 1075 °C.

Three Cu 100− x Ni x alloys, with x = 23, 33 and 45 at.%Ni, have been evaluated for use as substrates for coated conductors on the basis of measurements of their microstructure, crystallographic texture and hardness. It is found that high-temperature annealing after heavy rolling generates strong cube textures in each investigated alloy. For all of these alloys an increase in the annealing temperature from 800 to 1000 °C strengthens the cube texture and reduces the fraction of high angle grain boundaries. In the Cu–23 at.%Ni and Cu–33 at.%Ni alloys annealed at 1000 °C for 1 h, the fraction of the cube texture approaches 100% and the fraction of high angle boundaries is less than 4%. These two alloys are however very soft in the annealed condition. The cube texture in the Cu–45 at.%Ni substrate is slightly weaker than in the two other alloys, but this substrate is considerably harder, which makes it better suited for large scale production of superconducting tapes.

Rail wheel contact at switches and crossings (S&Cs) induces impact stresses along with rolling contact stresses, resulting in plastic deformation and eventually crack formation. Damaged and deformed wing rails of a manganese steel crossing are studied and the microstructure, hardness and 3D crack network within the steel are characterized. It is found that the surface of the rail receives the maximum deformation resulting in a hardened top layer. The deformation is manifested by a high density of twins and dislocation boundaries in the microstructure. A complex crack network is revealed in high resolution by X-ray tomography.

The effects of aging on the microstructural development and mechanical properties of a 3D-printed maraging steel have been investigated. The microstructures within printed, solution treated and aged samples are characterized by X-ray tomography and optical microscopy, as well as by scanning and transmission electron microscopy. The mechanical properties are estimated based on hardness measurements. The distribution of voids is found to be inhomogeneous, and even though the samples are 99.9% dense in the sample interior, the remaining voids affect significantly the hardness in the aged condition. In addition to precipitation, the aging treatment leads to formation of about 12% of reverted austenite. Together this leads to a strengthening of the material. Solution treatment results in homogenization of the microstructures such that after aging the solution treated samples are found to have higher strength than the samples that are just aged after printing. These results are discussed and compared to the aging behaviour of conventionally manufactured samples.

The onset of plastic yielding has been studied in samples of aluminum with near-micrometer average grain size using in situ tensile loading combined with synchrotron radiation. A white-beam Laue 3D micro-diffraction technique was used allowing the collection of diffraction signal from a volume with a resolution of 1 μm in all three dimensions. The orientation data obtained from the micro-diffraction are used to estimate the local variation in geometrically necessary dislocation density, and correction factors are suggested for voxels where neighbors are missing in either one or two dimensions. The results demonstrate a considerable heterogeneity in deformation in the early stages of plastic deformation.

Recent synchrotron measurements have shown the presence of local residual stress within nearly defect-free grains in partially recrystallized samples. A detailed quantification of such local stress is very important for understanding local boundary migration during recrystallization and for tailoring the microstructure of materials. In this study, we utilize high resolution electron backscatter diffraction (HR-EBSD, Wilkinson’s method) to investigate the local residual stress in recrystallized grains in a sample of partially recrystallized iron. The effects of reference selection on the strain distribution are also discussed.

The microstructure and crystallographic texture have been investigated in a Cu–45 at.%Ni alloy after heavy rolling and subsequent annealing at different temperatures. Cold-rolling to a von Mises strain of 5.7 produced a sample with an average boundary spacing along the normal direction of ~70 nm and a large fraction of high-angle boundaries (HABs), ~70 %. Annealing of this sample for 1 h at temperatures ≤450 °C causes structural coarsening, during which the fraction of HABs decreases. Annealing at higher temperatures results in pronounced discontinuous recrystallization accompanied by twinning. Large frequencies of twin boundaries contribute to high HAB fractions measured in the as-recrystallized condition. Cube-oriented grains demonstrate a size advantage compared to grains of other orientations, thus creating a strong cube texture in the recrystallized material. Further annealing of the recrystallized microstructure promotes grain growth, which leads to a significant strengthening of the cube texture and to a dramatic loss of HABs. After 1 h of annealing at 1000 °C the fraction of the cube texture reaches 99 % and the HAB fraction is 12 %.

A method is presented, which allows quantification of the roughness of nonplanar boundaries of objects for which the neutral plane is not known. The method provides quantitative descriptions of both the local and global characteristics. How the method can be used to estimate the sizes of rough features and local curvatures is also presented. The potential of the method is illustrated by quantification of the roughness of two recrystallization boundaries in a pure Al specimen characterized by scanning electron microscopy.

This introductory tutorial describes the so called 3 dimensional X-ray diffraction (3DXRD) technique, which allows bulk non-destructive structural characterizations of crystalline materials. The motivations and history behind the development of this technique are described and its potentials are sketched. Examples of the use of the technique are given and future trends and developments are suggested. The primary aim of the paper is to give 3DXRD novices an easy introduction to the technique and to describe a way from a dream to reality and new results.

It is shown how new discoveries and advanced experimental techniques in the last 25 years have led to paradigm shifts in the analysis of deformation and annealing structures of metals and in the way the strength of deformed samples is related to structural parameters. This is described in three sections: structural evolution by grain subdivision, recovery and recrystallisation and strength–structure relationships.

Columnar grained Ni is used as a model material allowing simultaneous non-surface investigations of the evolution of crystallographic orientations and deformation microstructures within individual grains as a function of rolling strain up to e = 0.7. Electron channelling contrast and electron backscattered diffraction are used to visualise microstructures and crystallographic orientations. It is found that both the microstructural and the textural development depend strongly on the initial grain orientation. A grain size effect is observed on the deformation-induced orientation scatter within the grains. Large grains have microstructure and orientation scatters similar to those observed in single crystals of similar orientation. The observations are interpreted based on a slip system analysis, considering the relative effects of the initial grain orientation and the interaction between neighbouring grains as well.

Three-dimensional X-ray diffraction has been used to study the growth kinetics of 1406 individual grains recrystallizing in 50% cold-rolled aluminium. It is found that each grain follows its own kinetics. The radial growth of individual grains is found to often be piecewise linear, and an explanation based on the cell block microstructure of cold-rolled aluminium is proposed. Grain-averaged activation energies of 793 individual grains are determined, and found to constitute a broad distribution. Reasons and implications of these findings are discussed.

A method to map the microstructure in deformed aluminum in three dimensions is presented. The method employs serial sectioning by mechanical polishing, and electropolishing to obtain a good surface quality, and orientation mapping of individual grains in each section by electron backscattered diffraction. Techniques to carefully align the sample and to accurately measure the thickness of the material removed in each serial section are described. A new method for stacking the two dimensional maps together to produce a three dimensional visualization of the microstructure is presented. The data are analyzed in terms of the deformation-induced orientation spread within each grain. In particular the advantage of using three dimensional data, as opposed to two dimensional data, is illustrated, by inclusion of information about the three dimensional morphology of a grain and its neighbors.

The microstructure and texture of commercial purity aluminum (AA1050) have been investigated after cold rolling to von Mises strains of 3.6 to 6.4 followed by recovery and recrystallization during annealing. The evolution of structural parameters of the deformed microstructure, such as boundary spacing and fraction of high-angle boundaries (HABs), did not reach saturation in the given strain range. Recovery was accompanied by structural coarsening and by a decrease in the fraction of HABs. The coarsening rate increased with increasing strain prior to annealing. Recrystallization nuclei were found to form both in deformation zones around coarse particles and in recovered lamellar structures. The process of recrystallization in the present material can thus be characterized as discontinuous recrystallization. In recrystallized conditions, the average grain size was related to the grain orientation: the mean size of grains having orientations of the rolling texture was smaller than the size of grains with other orientations. The orientation dependence of the recrystallized grain size was more pronounced in the samples rolled to ultrahigh strains.

A 30% deformed aluminum sample was mapped non-destructively using three-dimensional X-ray diffraction (3DXRD) before and after annealing to nucleation of recrystallization. Nuclei appeared in the bulk of the sample. Their positions and volumes were determined, and the crystallographic orientations were compared with the orientations of the deformed grains. It was found that nuclei with new orientations can form and their orientations have been related to the dislocation structure in the deformed grains.

The growth of individual grains during recrystallization in 96% cold-rolled pure nickel has been followed using electron backscatter pattern maps of the same surface area taken after each of several annealing steps. It was found that the growth is quite complex, with boundaries moving, stopping and moving again. The growth kinetics differ from grain to grain and, on average, cube-oriented grains grow the fastest. The growth of the grains has also been analyzed as a function of boundary misorientation. This analysis shows that there is no significant difference in misorientation distribution between boundaries that move and those that do not. This is contrary to the usual assumption that the boundary mobility and the migration rate depend on the misorientation across a boundary. This observation and the reasons for the faster growth of cube-oriented grains are discussed.

Computer simulations are used to study effects of an experimentally determined 3D distribution of nucleation sites on the recrystallization kinetics and on the evolution of the recrystallized microstructure as compared to simulations with random nucleation. It is found that although the experimentally observed clustering is not very strong, it changes the kinetics and the recrystallized microstructural morphology plus leads to a recrystallized grain size distribution, which is significantly broadened compared to that of random nucleation simulations.

The isothermal recrystallisation of commercial purity aluminium alloy AA1200 cold deformed to either a true strain of 2 (86·5% reduction in thickness) or 4 (98·2% reduction in thickness) was studied phenomenologically in each material by means of quantitative microscopy. The microstructural path descriptors, V V, the volume fraction recrystallised, and S V, the interfacial area density separating recrystallised grains from deformed grains were measured stereologically by electron backscatter diffraction and microstructural path model parameters were deduced for each strain. The effects of strain were delineated and compared with the results of recrystallisation in a slightly different commercial aluminium alloy AA1050 deformed to a true strain of 2·3.

Grain growth in an Al–0.1% Mn sample has been measured non-destructively using a three-dimensional X-ray diffraction (3DXRD) microscope. The 3-D grain morphology as well as the crystallographic orientation was determined for 483 grains in the illuminated volume prior to annealing. After annealing, a second map revealed that significant grain growth had taken place, with only 27 remaining grains in the same volume. The correlation between grain orientation, growth of grains and neighbouring relationships is explored.

A directionally solidified, high-purity nickel sample with a strong 〈0 0 1〉 fiber texture was cold rolled to 40% reduction. Electron backscattered diffraction (EBSD) was used to identify triple junctions (grain edges) before annealing the sample at 430 °C, after which further EBSD was performed to identify 17 recrystallization nuclei at the initially characterized triple junctions on the rolling plane. In addition, a longitudinal section was cut on which a further seven recrystallization nuclei were found and characterized. This characterization of all nuclei revealed that the majority of nuclei could be broadly associated with a 40° 〈1 1 1〉 misorientation to the matrix in which they formed, while a much lower percentage were found to have orientations as those of the local deformation substructure. However, a substantial fraction (around one-third) could not be associated with either of these types. Mechanisms for the formation of nuclei with new orientations are discussed, as is evidence of reorientation of material ahead of the recrystallization front.

Three single crystals of typical fcc rolling texture orientations—{112} (C), {123} (S), and {110} (B)—have been deformed by plane strain compression at room temperature, and the stored energy of deformation in each has been calculated from measurements in the transmission electron microscope (TEM) of dislocation boundary spacings and misorientation angles. The stored energy has been determined on two length scales: the single crystal scale and, for orientations in which localized glide bands (LGBs) are present, on the local length scale. On the crystal scale, it is found that the stored energy shows a strong dependence on the crystallographic orientation; the highest is for the C orientation and the lowest is for the B orientation. For the C and S orientations, where LGBs develop during deformation, the differences in stored energy between the LGB and matrix regions can be as large as the differences between the average values for each single crystal. The observed variation of stored energy on the crystal scale and the local scale can be related to the experimental observations of the flow stress and to the recrystallization behavior of the three crystal orientations.

The development of texture and microstructure during recrystallization of pure nickel rolled to very high strains has been investigated. Low-temperature annealing was chosen in order to separate the effects of recrystallization and grain growth. Particular attention was focused on the nucleation and growth of the cube orientation texture component, and on the effect of twinning in producing texture components of other orientations. The growth rates for recrystallizing grains of cube and non-cube orientations were analyzed from the EBSP data using an extended Cahn–Hagel method. Within the estimated experimental errors the growth rates of both orientation classes remain constant during recrystallization, with the cube orientation grains having a higher growth rate by a factor of ∼3. Some minor recrystallization texture components result from twinning, with the role of twinning being most important in the early stages of recrystallization.

Recrystallization in copper deformed by dynamic plastic deformation was investigated using electron backscatter diffraction. The recrystallized grains show a broad size distribution. The kinetics of grains of different sizes is observed to be different: In the beginning of recrystallization, the area fraction of small recrystallized grains increases rapidly. At later stages of recrystallization, the area fraction of small recrystallized grains is stable, while the area fractions of medium and large recrystallized grains increase. Correlation between the broad grain size distribution (and its evolution) and the heterogeneous deformed microstructure is discussed. © Published under licence by IOP Publishing Ltd. Conference code: 114064; Cited By :1; Export Date: 18 November 2021; Conference Paper; References: Leffers, T., Ray, R.K., (2009) Prog. Mater. Sci., 54, p. 351; Bhattacharyya, A., Rittel, D., Ravichandra, G., (2005) Scr. Mater., 52, p. 657; Luo, Z.P., Mishin, O.V., Zhang, Y.B., Zhang, H.W., Lu, K., (2012) Scr. Mater., 66, p. 355; Hong, C.S., Tao, N.R., Lu, K., Huang, X., (2009) Scr. Mater., 61, p. 289; Morri, K., Meching, H., Nakayama, Y., (1985) Acta Mater, 33, p. 379; Lin, F.X., Zhang, Y.B., Tao, N.R., Pantleon, W., Juul Jensen, D., (2014) Acta Mater, 72, p. 252; Wu, G.L., Juul Jensen, D., (2008) Mater. Charact., 59, p. 794; Pande, C.S., (2000) Proc. 21st Risø Inter. Symposium on Mater. Sci., p. 491; Lin, F.X., Zhang, Y.B., Pantleon, W., Juul Jensen, D., Submitted; Li, Y.S., Tao, N.R., Lu, K., (2008) Acta Mater, 56, p. 230; Li, Y.S., Zhang, Y., Tao, N.R., Lu, K., (2008) Scr. Mater., 59, p. 475; Yan, F., Zhang, H.W., (2012) J Mater. Sci. Technol., 28, p. 289

Three-dimensional (3-D) microstructural characterization has proven to be indispensable for the thorough understanding of the often highly complex microstructures studied in materials science. However, most 3-D characterization techniques of opaque materials such as metals and ceramics are destructive and therefore prohibit 3-D studies of the dynamic microstructural evolution processes. In this paper we describe two complimentary techniques capable of nondestructive 3-D characterization and provide examples of the application of these techniques to investigate microstructural evolution processes in metallic systems.

Three-dimensional X-ray diffraction (3DXRD) is used to characterize the nucleation and early growth of individual bulk nuclei in situ during recrystallization of 92% cold-rolled copper. It is found that some cube nuclei, but not all, have a significantly faster initial growth than the average growth kinetics. These results are discussed and compared to previous 3DXRD results for recrystallization of aluminum alloys, and implications of the results on modeling of recrystallization are considered. Finally, a new 3DXRD technique suitable for non-destructive 3D characterization is outlined and its potential for recrystallization studies is discussed.

This paper shows that interfacial area density between transformed grains during nucleation and growth transformations and the contiguity are useful descriptors of microstructural evolution. These descriptors are evaluated analytically and compared with results from computer simulation. Usage of these descriptors makes microstructural path analysis even more reliable and robust.