Materials Science Forum Vols. 715-716

Abstract: A combination of electron backscatter diffraction (EBSD) and focused ion beam (FIB) techniques were used to obtain 3D EBSD data in an investigation of dynamic recrystallization in a Cu-2%Sn bronze alloy. The results of this investigation show the origin of the nucleation sites for dynamic recrystallization and also elucidates the orientation relationship of the recrystallized grains to the deformed, prior grains and between the dynamically recrystallized grains.

Abstract: The understanding of the dynamics of substructures during deformation and annealing is fundamental in our ability to predict microstructural and physical properties such as rheological behaviour of crystalline materials. Here, we present an overview of new insights into substructure dynamics through a combination of in-situ heating experiments, detailed Electron Backscatter Diffraction (EBSD) analysis and numerical modelling.

Abstract: Deformation and recrystallization textures in nanocrystalline nickel with average grain size of 20 nm were investigated using X-ray diffraction, electron microscopy and differential scanning calorimetry. The deformation behaviour of nanocrystalline nickel is quite complicated due to intervention of other deformation mechanisms like grain boundary sliding and restoration mechanisms like grain growth and grain rotation to dislocation mediated slip. Recrystallization studies carried out on the deformed nanocrystalline nickel showed that the deformation texture was retained during low temperature annealing (300°C), while at higher temperature (1000°C), the texture got randomised. The exact mechanism of texture formation during deformation and recrystallization has been discussed.

Abstract: Within the last decade a number of x-ray diffraction methods have been presented for non-destructive 3D characterization of polycrystalline materials. 3DXRD [1] and Diffraction Contrast Tomography [2,3,4] are examples of such methods providing full spatial and crystallographic information of the individual grains. Both methods rely on specially designed high-resolution near-field detectors for acquire the shape of the illuminated grains, and therefore the spatial resolution is for both methods limited by the resolution of the detector, currently ~2 micrometers. Applying these methods using conventional far-field detectors provides information on centre of mass, crystallographic orientation and stress state of the individual grains [5], at the expense of high spatial resolution. However, far-field detectors have much higher efficiency than near-field detectors, and as such are suitable for dynamic studies requiring high temporal resolution and set-ups involving bulky sample environments (e.g. furnaces, stress-rigs etc.)

Abstract: The evolution of cube texture has been investigated in pure Ni (~99.97%) following ultra high straining by Accumulative Roll Bonding (ARB) and annealing. Fully annealed sheets of pure Ni with average recrystallized grain size of ~28 (henceforth termed as fine grained starting material) and 650 µm (henceforth termed as coarse grained starting material) were used as the starting material for the ARB processing. ~50% reduction was imparted in each cycle of ARB and the process was carried up to 8 cycles resulting in an accumulated equivalent strain (ε_eq) of 6.4. The deformed materials were subsequently annealed at temperatures ranging between 300 to 800°C for one hour. In addition few samples were annealed at 300°C for different time intervals to observe the evolution of texture components. In all cases textures were carefully characterized using Electron Back Scatter Diffraction (EBSD) technique.

Abstract: Al-Sn alloys for tribological applications are industrially important alloys which have attracted little attention over their history. Being cold rolled directly from thin cast slabs and consisting of two ductile phases, their processing and physical behaviour are distinct from classical Al-Alloys. During cold rolling, the coarse-grained, random texture of the slab is transformed into the classical rolling texture of a fine-grained Al-alloy, with elongated Al-grains delimited by thin Sn-ribbons. During annealing at 300°C, the interior of the Al-grains recrystallises rapidly while the liquid Sn-phase migrates toward Al-grain triple lines to form a reticular structure. A weak texture, dominated by Goss and P is produced. Grain growth within the original cold-rolled grains is fast, but once the recrystallised grain size reaches the length scale of the second-phase distribution, it slows down and both phases coarsen simultaneously, accompanied by a significant texture change.

Abstract: Grain growth processes in real polycrystalline materials are mostly characterized by the presence of restraining forces, originating, among others, from second phase particles dispersion (Zener drag) or solute atoms segregating at the grain boundaries (solute drag). Both the restraining mechanisms were introduced in the framework of the statistical theory of grain growth, showing their peculiar effects on kinetics and on grain size distribution evolution [1,2,. The present work moves from the previous results and gives a further clarification of pseudo-steady state kinetics occurring under particular solute drag inhibition intensity and will discuss it in comparison with grain growth stagnation conditions produced by Zener drag. In case of second phase particle inhibiting grain growth, the normal case in real systems is the time and temperature dependence of the inhibition intensity due to the evolution of precipitates (e.g. Ostwald ripening. Such evolutions of inhibition, which typically drops with increasing temperature, can cause microstructure instabilities like abnormal grain growth or secondary recrystallization. It is thus introduced in the model a time-temperature depending inhibition drop, which influences both kinetics and grain size distribution evolution. Conditions for the onset of particular effects like abnormal grain growth are assessed and discussed.

Abstract: Modern steel plate manufacture relies on the manipulation of recrystallisation and grain growth in order to obtain maximised and precise mechanical properties from low-alloyed feedstock. The models that describe this metallurgical process nowadays inform the design of the plant itself. They are also capable of application to the on-line control of rolling, as well as to several of the ancillary mill operations.

Abstract: Abnormal grain growth (AGG), which is also called the secondary recrystallization, often takes place after primary recrystallization of deformed polycrystalline materials. A famous example is the evolution of the Goss texture after secondary recrystallization of Fe-3%Si steel. A selective AGG of Goss grains has remained a puzzle over 70 years in the metallurgy community since its first discovery by Goss in 1935. We suggested the sub-boundary enhanced solid-state wetting as a mechanism of selective AGG of Goss grains. According to this mechanism, if Goss grains have sub-boundaries of low energy, they have an exclusively high probability to grow by solid-state wetting along a triple junction compared with other grains without sub-boundaries. This aspect has been confirmed by Monte-Carlo and Phase Field Model simulations. The simulations showed that if the abnormally-growing grain has a high fraction of low energy boundaries with the matrix grains, it favors the sub-boundary enhanced solid-state wetting and produces many island and peninsular grains frequently observed near the growth front of abnormally-growing Goss grains. For example, the {111}<112> orientation has a S9 relationship with a Goss grain. Therefore, grains with the {111}<112> orientation provide a favorable condition for sub-boundary enhanced solid-state wetting. Three or four-sided grains with convex-inward boundaries, which are observed on a two-dimensional section of polycrystalline structures, are not shrinking but are growing, indicating that they are growing by wetting along a triple junction. These and other microstructural evidences of solid-state wetting could be observed relatively easily near the growth front of abnormally-growing Goss grains. The existence of sub-boundaries exclusively in abnormally-growing Goss grains has been experimentally confirmed. In order to understand why only Goss grains have sub-boundaries, the cold rolling process of the hot-rolled Fe-3%Si steel was analyzed by finite element method (FEM). The analysis showed that a small portion of Goss grains formed during hot rolling survives after cold rolling; the survived Goss grains have the lowest stored energy and are expected to undergo only recovery without recrystallization, producing sub-boundaries.

Abstract: The microstructure evolution in commercial AlMgSi alloys during and after extrusion of a simple U-shaped profile has been modelled. The strain, strain rate and temperature along a set of particle paths are taken from FE-HyperXtrude simulations and used as input to the work hardening model ALFLOW, to predict the evolution of the subgrain size and dislocation density during deformation. As soon as the profile leaves the die, the subsequent recovery and recrystallization behaviour is modelled with the softening model ALSOFT. This procedure enables the modelling of recrystallization profiles, i.e. the fraction recrystallized through the wall thickness of the extruded profile. The sensitivity to chemistry (alloy composition), profile deflection and the cooling rate at the die exit has been investigated by means of a set of generic modelling cases.