Recrystallization Of Single Crystals Research Articles

Peculiarities of microstructure of YBa2Cu3O7-δ single crystals heat treated under different conditions

The microstructure of single-crystal YBa2Cu3O7-δ samples has been studied after a reaction with water vapor at 200–300°C and after restoring annealings at 400–930°C. The absorption of water from air during low-temperature annealing was found to lead to the disappearance of twin structure and appearance of stress fields around precipitated particles. During restoring annealing at 930°C, the primary recrystallization of single crystals takes place. The initial twin structure was not formed in the course of subsequent oxidation.

Simulations of deformation and recrystallization ofsingle crystals of aluminium containing hard particles

The deformation of a single crystal of aluminium in the Goss orientation{011}⟨100⟩ containing a coarse particle of silicon was modelled by using afinite-element (FE) code based on the crystal plasticity approach. Thesimulations clearly captured the heterogeneous deformation of the aluminiummatrix, resulting in a region of high deformation in the vicinity of the hardparticle, surrounded by a region where the amount of deformation wassignificantly lower. The evolution of the corresponding deformationsubstructure during annealing was simulated using a Monte Carlo technique. Thesimulations clearly demonstrated the discontinuous evolution of the subgrainsin the deformation zone to form recrystallization nuclei around the hardparticle, and the subsequent growth of these nuclei to consume the matrixregion around the particle. For plane strain compression up to εzz = -0.4 that was usedin this study, the deformation texture components near the particle consistedof rotations up to 20° from the initial Goss orientation about the transversedirection. Recrystallization simulations captured the formation andgrowth of nuclei from the deformation heterogeneities existing near the hardparticle and predicted a significant strengthening of the orientations presentin the particle deformation zone. The simulation results are shown to capturemany of the experimentally observed features of deformation andrecrystallization textures in aluminium single crystals containing coarseparticles of silicon.

Dynamic recrystallization in Al single crystals revealed by rapid X-ray Laue method

An experimental study on the microstructure development and stress-strain behavior during high temperature deformation of aluminum single crystals was made by the use of an in-situ X-ray technique. The main purpose of this experiment was to detect the dynamically recrystallized grains during deformation. The specimens for the compressive test (3 x 3 x 6 mm 3 ) were prepared from high purity (five nine grade) Al single crystal ingots. Compressive deformation was made at 373-473 K with initial strain rate 10 -4 -10 -3 s -1 using a test machine designed so as to fit on the camera stage of the X-ray apparatus. The crystallographic orientation was chosen as the compression axis. Transmission Laue diffraction patterns was recorded during deformation. The utilization of imaging plates. Fuji ST-VA, instead of conventional photographic emulsion films, enabled to reduce the exposure time down to < 2 s for the X-ray radiation generated from a normal focus W-tube operated at 1.4 kW. The deformed specimens were subjected to optical microscopy. For all the deformation conditions employed in the present work, a large stress fall was observed after the first stress peak. At 473 K, the strain corresponding to the first stress peak was around 0.15 and tended to increase with decreasing strain rate. X-ray Laue spots began to streak as strain increased, and new spots without streak appeared at around or just after the first stress peak, indicating that new fresh grains had been dynamically formed. These results are in consistent with those of the previous workers. Mechanisms of dynamic recrystallization in single crystals were discussed.

Creep and Evolution of Dynamic Recrystallization in Single Crystals of Ti-48at%Al with Different Orientation between Stress Axis and γ Lamellar Plate

Creep and Evolution of Dynamic Recrystallization in Single Crystals of Ti-48at%Al with Different Orientation between Stress Axis and γ Lamellar Plate

Influence of external constraint on deformation banding of copper single crystals of {110} orientations

Extensive researches have been done on deformation and recrystallization of single crystals. One main reason is that complicated intergranular interactions can be avoided during deformation of single crystals and hence single crystals are very suitable for fundamental researches. However, it is also due to this major difference, the results obtained from single crystals are not directly applicable to polycrystalline materials. In this paper, the influence of external constraint on the deformation behavior of copper single crystals with {l_brace}110{r_brace} orientations was investigated by embedding them into metal frames of different strengths. Hence, the deformation environments of the embedded single crystals are in between those of unconstrained single crystals and crystals in ordinary polycrystalline aggregates. Thus, the present work should help to bridge the gap between the present understandings on the deformation of single crystals and polycrystalline samples.

Mechanism of Diffusion Induced Recrystallization in Single Crystals of Copper

Mechanism of Diffusion Induced Recrystallization in Single Crystals of Copper

Diffusion induced recrystallization in single crystals of copper

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Dynamic softening of copper during deformation at high temperatures and strain rates

The response of single crystals of pure copper to hot deformation was investigated and found to be similar to that of a polycrystalline aggregate. The flow curve exhibited an oscillation in the flow stress before attaining a steady state when deformed under the conditions of low Z (Zener-Holloman parameter) and a single maximum when deformed under conditions of high Z. However, the strain to the peak stress was consistently higher for single crystals than for polycrystals deformed under identical conditions. The critical strain to initiate dynamic recrystallization in single crystals was found to be less than the strain to the peak stress, and the difference gradually increased upon increasing Z. Interrupted compression tests performed on polycrystalline copper and aluminium demonstrated that dynamic recrystallization is essentially quasi-static in nature. However, dynamic recovery is achieved through the accelerated softening kinetics which are assisted by the applied stress and/or strain rate. Both optical and transmission electron microscopy observations reveal that the dynamically recrystallized structure is essentially composed of annealing twins. The association of the occurrence of annealing twins with dynamic softening has led to the proposal of a mechanism for dynamic recrystallization. This mechanism can account for the structural instability which must occur within the deformation time necessary for dynamic recrystallization. In this view, the role of stacking fault energy in initiating dynamic recrystallization is exerted through its influence on twin boundary interfacial energy.