Recrystallization and Grain Growth

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Authors: Duk Yong Yoon, Young Kyu Cho, Hyun Min Jang
Abstract: Flat surfaces and grain boundaries lying on low crystal planes are singular corresponding to the cusps in the polar (Wulff) plots of their energy against their orientation. The theoretical analysis of the entropy effect at high temperatures shows that these interfaces undergo roughening transitions. The molecular dynamics simulations also show disordering to liquid-like structures at high temperatures that can be interpreted as the roughening transition. Experimentally, singular flat surfaces and grain boundaries become curved at high temperatures or with additives, indicating their roughening transition. The grain boundaries in polycrystals are often faceted with hill-and-valley shapes and their defaceting at high temperatures also show their roughening transition.
825
Authors: Fuyuki Yoshida, Masato Uehara, Kenichi Ikeda, Hideharu Nakashima, Hiroshi Abe
Abstract: Migrations of <110> tilt S 11 and S 27 boundaries in 99.99% purity aluminum have been investigated by Sun and Bauer technique as a function of temperature. In the S 11 tilt boundary, the activation energy for grain boundary migration is about 1/2 of the energy for Al-atom bulk-diffusion, indicating that the boundary motion may be governed by the grain boundary diffusion. While in the S 27 tilt boundary, the activation energy for grain boundary migration is about 125kJ/mol, which agrees with the energy for Al-atom bulk-diffusion. Study of boundary structure observation by high resolution electron microscopy revealed that the grain boundary structure of S 27 tilt boundary was consisted of edge dislocation array in which a space between dislocations was very short. It is considered that climb motion of the dislocations controlled to the motion of tilt boundaries consisted of edge dislocation array. From these results, it is concluded that the boundary motion of S 27 tilt boundary may be governed by climb motion of their dislocations controlled by Al-atom bulk-diffusion.
835
Authors: Roger D. Doherty, Elizabeth Hoffman, Christopher Hovanec, Arnaud Lens
Abstract: The prior literature on abnormal grain coarsening (AGC) at low volume fractions (f) of stable second phase particles in high purity Al alloys is reviewed and reanalyzed in the light of developments in modeling particle inhibition of grain boundary migration. With the usual assumptions (i) of incoherent particles that retain their shape on contact with the grain boundaries and (ii) that all the grain boundaries are equally mobile, it appears impossible to account for process of AGC. Normal grain coarsening (NGC) is shown to be less inhibited by the particles than is AGC. This idea is explored using a new but simple model of particle inhibition by curvature removal. The curvature of the smallest grains is always larger than that of the larger grains. Two possible hypotheses to overcome this difficulty are proposed: First the possible change of shape of particles on slowly moving grain boundaries, of grains with near 14 neighbors should, after a small increment of NGC, promote AGC at low values of the volume fraction f. The second hypothesis involves the observed high density of immobile, low angle grain boundaries (LAGBs) found in recent experiments on high purity Al-Fe-Si alloys cast with very coarse grain sizes. These alloys undergo rapid AGC even at higher values of f (> 0.01). These LAGBs are expected to inhibit the shrinkage of many of the small grains, whose loss is the fundamental mechanism of NGC.
843
Authors: Yoshiyuki Ushigami, Tomoji Kumano, Tsutomu Haratani, Shuichi Nakamura, Shigeto Takebayashi, Takeshi Kubota
Abstract: Mechanism of Goss secondary recrystallization in grain-oriented silicon steel has been investigated by temperature gradient annealing and by in situ observation utilizing synchrotron x-ray topography. The results support the selective growth theory. Migration of Goss grains is controlled by second phase particles (inhibitor) and sharper Goss grains, which have higher frequency of CSL boundaries to the matrix, start to grow preferentially while the other matrix grains are stagnated by inhibitor. CSL boundaries are supposed to have lower grain boundary energy, thus suffer lower pinning force from the inhibitor and start to migrate at higher inhibition level. Based on this model, we have made a computer simulation and have found that this model successfully depicts the important features of secondary recrystallization; grain growth behavior of secondary grains, secondary grain size and sharpness of Goss texture.
853
Authors: Carlos Capdevila, Tommy De Cock, Francisca García Caballero, Carlos García-Mateo, Carlos García de Andrés
Abstract: The influence of the deformation grade on the recrystallised grain size has been studied in the AISI 304 stainless steel. Therefore, cold rolled samples of this material with reductions varying between 30% and 80% were annealed at different temperatures and subsequently quenched. The mean austenitic grain sizes were measured and compared. Moreover, the correlation between the variation of the thermoelectric power and the grain growth was investigated for each degree of prior deformation.
863
Authors: Marco Antônio Da Cunha, Sebastião Da Costa Paolinelli
Abstract: The evolution of annealing texture of non-oriented grain silicon steel as a function of annealing temperature was investigated from hot rolled samples taken from industrial production. Hot band samples were annealed at 900°C, cold rolled to final thickness of 0.5mm in a single stage cold rolling process or in two stages with intermediate annealing at 900°C, and final annealed in the temperature range from 540°C to 980°C. The results show that the [001]||RD fibre is an important recrystallization texture component, but it may be consumed by further grain growth and become a minor component. The effect of grain growth in the temperature range investigated seems to be that of strengthening the main components at the expenses of the others. The results suggest that to avoid the reduction of the [001]||RD fibre on grain growth a volume fraction ratio between the texture components (111)[112] and (110)[001] close to unity is necessary after recrystallization. This can be obtained under conditions that enhance [001]||RD fibre on recrystallization, such as: strong [111]ND fibre in the deformation texture, large initial grain size and enhanced grain boundary mobility, by proper composition and purity.
869
Authors: I.M. Fielden
Abstract: The development of the converter plate detector has allowed the generation of real-time, in-situ image sequences of evolving microstructures in model and industrial polycrystalline metals. The principal metals investigated were steel, aluminium and gold. The raw video results allow a number of qualitative statements to be made about grain growth behaviour in these systems and some simplistic quantitative statements. However, the sheer volume and variety of data available in the time-stream of micrographs presents its own problems in identifying and extracting the information most useful for rigorous characterisation of the behaviour of a dynamically evolving microstructure. We present and discuss our approach to the analysis of this data and results of that analysis.
875
Authors: Yan Hu, Valerie Randle, Terry Irons
Abstract: A matrix of twelve laboratory heat treated iron-silicon specimens were investigated to identify the microtextures, grain misorientations and grain size distributions present and to relate them to the various silicon contents and annealing cycles. The steel grades examined contained either 1.0%, 2.4% or 3.0% silicon. The results showed that the higher strain levels present in the hot rolled microstructures as silicon content increased created a greater driving force for recovery, recrystallisation and grain growth processes.
881
Authors: N. Maazi, N. Rouag, Richard Penelle
Abstract: A grain growth simulation based on the concept of grain boundary migration driven by the radius curvature has been tested to study the abnormal grain growth (AGG) of the Goss grains in silicon steels in presence of particles. In the classical simulation of AGG, the grain size is generally assumed to be homogeneous. In order to introduce the influence of the morphological and crystallographic heterogeneities on AGG around the Goss grain, the simulation procedure has been implemented using as starting state an experimental microstructure characterized by Orientation Imaging Microscopy (OIMTM). Abnormal growth results are compared for the two grades, Hi-B and CGO of Fe-3%Si alloys. It has been notably shown that the large grains resist AGG so that the Goss grain shape becomes anisotropic.
887
Authors: Kenichi Murakami, Jacek Tarasiuk, H. Réglé, Brigitte Bacroix
Abstract: Texture formation through strain induced boundary migration (SIBM) was investigated. Temper rolling reduction before final annealing for SIBM was varied between 0 and 26% and grain sizes and textures were measured using EBSD. In the specimen which was temper rolled to 5%, in which grain growth by SIBM occurred most efficiently, a strong Goss component (which was a minor component after rolling), developed during annealing. From the EBSD image quality analysis, it was found that stored energy increased significantly in the Goss component with strain (from 5 to 9 %), whereas it was always relatively small in the D-Cube component ({001}<110>), compared to Goss and g-fibre components. Based on these results, a mechanism of grain growth by SIBM was suggested. Texture evolution during annealing could thus be explained by the hypothesis, speculated from the analysis of orientation stability, that D-Cube grains are associated with more homogeneous dislocations distributions than Goss grains, in which the co-existence of high and low dislocation density zones could favour grain growth by SIBM.
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