Formation Of Recrystallization Nuclei Research Articles

A Multilevel Physically Based Model of Recrystallization: Analysis of the Influence of Subgrain Coalescence at Grain Boundaries on the Formation of Recrystallization Nuclei in Metals

This paper considers the influence of subgrain coalescence at initial high-angle boundaries on the initiation and growth of recrystallization nuclei (subgrains) under thermomechanical treatment. With certain processing regimes, adjacent subgrains in polycrystalline materials can be assembled into clusters during coalescence. Subgrain clusters at high-angle boundaries are the preferred potential nuclei of recrystallization. Coalescence is one of the dynamic recovery mechanisms, a competing process to recrystallization. When intensive coalescence develops on both sides of the grain boundary, recrystallization slows down or even stops. The problem formulated is solved using a multilevel modeling apparatus with internal variables. Application of the statistical multilevel model modified to take into account the local interaction between crystallites makes it possible to explicitly describe dynamic recrystallization and recovery. The results of modeling the behavior of a copper sample are presented and the effects of temperature, deformation velocity and subgrain structure on the formation and growth of recrystallization nuclei at arbitrary and special grain boundaries during coalescence are analyzed.

On the formation of recrystallization nuclei in austenitic nitrogencontaining steel under hot deformation

This article presents the results of studying the structure of high-strength corrosion-resistant austenitic nitrogen-containing steel formed as a result of hot deformation. It was found that, depending on the temperature, degree and rate of deformation, the mechanism of formation of nuclei of dynamic recrystallization changes. At temperatures above 1100°C, nuclei are formed due to bending and subsequent migration of grain boundaries; however, with a decrease in temperature and an increase in the degree and rate of deformation, subgrains become centers of recrystallization near the initial boundaries.

The crystallographic relationship of molybdenum textures after hot rolling and recrystallization

Using the method of orientation microscopy, based on electron backscatter diffraction (EBSD), the texture of molybdenum sheet, produced by hot rolling at 1100°C with a total strain exceeding 90%, was characterized. Throughout its whole thickness, the molybdenum texture consisted of a set of stable orientations: (001)[110], {112}〈110〉, {111}〈112〉, {111}〈110〉. During recrystallization at 1200°C {001}〈110〉 orientation became weaker, while the other orientations enhanced. The orientations of recrystallized grains were related with the orientations of deformed grains by rotations at defined angles around their axes 〈110〉. The formation of recrystallization texture can be explained by the migration of CSL boundaries of Σ9 type and/or the formation of recrystallization nuclei at the Σ3 and Σ11 CSL boundaries, which was preceded by the appearance of CSL misorientations between the components of deformed texture.

Precipitation and Recrystallization Behaviors of a High-Nitrogen Austenitic Stainless Steel Aging at 90°C

The behaviors of precipitation and recrystallization aging at 900 after cold work in a Fe-18Cr-12Mn-0.48N high-nitrogen austenitic stainless steel were investigated by means of optical microscopy (OM) and transmission electron microscopy (TEM). The results show that precipitation and recrystallization occur simultaneously after aging at 900 for 10min. The precipitates firstly appear at dislocation, sub-boundary and inside the subgrain. Precipitation at these positions hinders the formation of recrystallization nucleus. With aging time increasing, precipitates appear in the recrystallized grain boundary and inside the grain. Precipitation at these positions hinders the growth of the recrystalized grains.

Primary recrystallization mechanisms in ceramic materials

Data on the mechanisms of primary recrystallization in covalent type ceramics under temperature-and-pressure treatment are generalized and discussed. There are three types of structural transformations governing nucleation during primary recrystallization. I. Formation of intragrain boundaries. As a result of plastic shears boundaries appear to be kinked due to dislocation pile-ups (materials based on 2H BN, 6H SiC). With deformation by total dislocations the boundaries arise as a result of dynamic recovery due to rebuilding of dislocation pile-ups (AlN, β-Si3N4, TiB2). II. Twinning. This structural transformation promotes the formation of recrystallization nuclei in the following cases: a) with insertion of lattice dislocations into the boundaries of strain-induced twins; b) with formation of annealing twins; c) with development of multiple twinning near grain boundaries (3C BN). III. Structural transformations in migrating boundaries: a) splitting of boundaries and ternary junctions (3C BN); b) local bulging of boundaries (3C BN); c) generation of high-angle and platelet twins (3C BN); d) plastic rotation of material microvolumes near grain boundaries (3C BN, SiC).

Single Grain Orientation Measurements Applied to the Formation and Growth of Recrystallization Nuclei

Measurements of the crystallographic orientation of individual grains provide information on the spatial arrangement and distribution of orientations in a crystalline solid, i.e. on the orientation topography, which can be utilized to establish a basis for a deeper understanding of the microstructural mechanisms during deformation and recrystallization of metallic materials.Techniques for the convenient measurement of single grain orientations with high accuracy by evaluation of Kikuchi diagrams in a TEM and SEM (EBSD) are introduced. The principles of Kikuchi pattern formation as well as the measuring and evaluation procedures are outlined. Particular attention is focused on the automation of pattern indexing in order to provide fully automated evaluation routines. The unique potential of these techniques is demonstrated by two examples pertaining to the microstructural evolution during the formation of recrystallization nuclei and their subsequent growth.

EBSP: A powerful tool in studying recrystallization of metals

The Electron Back Scattering Pattern Technique (EBSP), for measurements of crystal orientations is now a well established technique for microtexlure detennination. The application of the technique to material problems has increased quite substantially the last years, both in basic research and in more industry related problems. When studying the recrystallization process in detail a relatively large area of a specimen has to be investigated to obtain good statistical results. With a resolution of the order of 0.5-1 μm and a short processing time the EBSPtechnique has shown to be advantageous compared to TEM on one side and X-ray and neutron diffraction on the other. By the EBSP-technique we are able to follow the local texture evolution during transformation and are at the same time able to analyse changes in the untransfonncd matrix (i.e. subgrain growth etc.).It is well accepted that the formation of recrystallization nuclei is a highly heterogeneous process.

Structure of well-defined deformation bands and formation of recrystallization nuclei in aluminium

AbstractIn order to investigate by transmission electron microscopy the same type of deformation band before and after annealing a study was made of the microstructure of a twisted aluminium crystal. Between the mainly single slip regions, bands of multiple slip were observed, with the development of misoriented deformation bands between the single and multiple slip regions. For one of the two types of deformation band, with a local misorientation of 25° over 15–25 μm the subgrains in the section studied were found to be equiaxed with a small spread of subgrain sizes but a large spread in subgrain angles (0.5–10°). On annealing, large subgrains developed which were somewhat elongated along the band, and these subgrains, which had the orientation of the single slip region, invaded the multiple slip regions. The nucleation mechanism was equivalent to straininduced boundary migration of the artificial 25° boundary produced by the deformation. The evidence of the microstructural changes indicated that a...

On the formation of recrystallization nuclei with cubic orientation in a cold rolled aluminum sheet

On the formation of recrystallization nuclei with cubic orientation in a cold rolled aluminum sheet

Keimbildung bei der Rekristallisation von Molybdän

A study by transmission electron microscopy has been made of the recrystallization of 99.95% pure molybdenum which has been 80% deformed by cold-rolling. The formation of recrystallization nuclei was observed to occur by the growth of subgrains as well as subgrain regions and by strain induced boundary migration. These mechanisms occurred simultaneously side by side.

Recrystallization of electrolytic iron

1. An increase of the initial recrystallization temperature of electrolytic iron as compared with pyrometallurgical iron is due to the large amount of oxygen and oxygen-containing impurities in the metal, which pin dislocations and inhibit the formation of recrystallization nuclei. 2. With increasing initial hardness of the coating the initial recrystallization temperature and the grain size increase.

Microstructures and Recrystallization of Cold-Rolled Single Crystals of Pure Iron

The substructures and recrystallization of the cold-rolled iron crystals with different initial orientations have been studied by transmission electron microscopy. When the crystals as-rolled are annealed at increasing temperature, dislocations forming cell structure rearrange to cause subgrains, whose orientations are found among those of the cells, and then recrystallized grains generally appear among the subgrains. The recrystallized grains are exclusively found in the matrix made up of the subgrains having smaller size as well as larger misorientation. There is strong reluctance to recrystallization when most of the segment of the subgrain boundaries consist of dislocation network resulting from the dislocation reaction such as 1/2a[111]+1/2a[1̄1̄1]→a[001]. The subgrain growth due to the coalescence is found from the close examination of the distribution of dislocations in the subgrains. The formation of recrystallization nucleus and the recrystallization tendency are discussed on the basis of the coalescence mechanism.

Effect of hydrostatic pressure on the kinetics of recrystallization in high-purity copper

The kinetics of recrystallization of polycrystalline copper (99,999% purity) cold-rolled to 98% reduction have been determined by means of an X-ray diffraction technique for the temperature range 80°–170°C at atmospheric pressure and at 42 kilobars. The high pressure is found to retard both the initiation and the rate of recrystallization. For both atmospheric and high pressure, the fraction of recrystallization, x, as a function of time, t, corresponds to an equation of the form: x = 1 − exp [−tτk] The retardation results from a change in the rate constant τ; the value of the exponent k is unchanged by pressure. The activation energy for recrystallization, obtained from the temperature dependence of τ, is 19.5 ± 1.5 kcal/mole for both pressures. These results are shown to be in keeping with the Bailey-Hirsch model for recrystallization. It is demonstrated that the observed pressure effects exclude the possibility that, for heavily cold-worked copper, the formation of recrystallization nuclei can be described by any of the several models which involve the formation of mobile high-angle boundaries by the movement of dislocations on annealing. Les auteurs ont étudié, par une technique de diffraction des rayons X, la cinétique de recristallisation du cuivre polycristallin, (pur à 99,999%), laminé à froid avec 98% de réduction de section, dans le domaine de températures de 80 à 170°C, à la pression atmosphérique et à 42 kilobars. On observe que la haute pression retarde à la fois le début de la recristallisation et la vitesse de celle-ci. A la pression atmosphérique et à haute pression, la fraction recristallisée x est donnée en fonction du temps t par une équation de la forme x = 1 exp[ − t(τ)k]. Le retard apporté par la haute pression se manifeste par une modification de la constante de vitesse τ; la valeur de l'exposant k n'est pas modifiée par la pression. L'énergie d'activation de la recristallisation, dérivée de la loi de variation de τ en fonction de la température, est 19,5 ± 1,5 kcal/mole pour les deux pressions. Les auteurs montrent que ces résultats sont en accord avec le modèle de recristallisation de Bailey-Hirsch. Ils démontrent que l'influence de la pression qu'ils observent exclut la possibilité que, dans le cas du cuivre fortement déformé à froid, la formation des germes de recristallisation puisse se décrire par l'un des modèles qui admettent la formation de frontières mobiles à angle élevé par le mouvement des dislocations au cours du recuit. Die Rekristallisationskinetik von 98% ig kaltgewalztem, polykristallinem Kupfer (Reinheit 99,999%) wurde mit Hilfe einer röntgenographischen Methode im Temperaturbereich von 80°– 170°C bei Atmosphärendruck und bei 42 Kilobar untersucht. Bei hohem Druck wird demnach sowohl der Beginn als auch die Geschwindigkeit der Rekristallisation verzögert. In beiden Fällen gilt für die Zeitabhängigkeit des rekristallisierten Anteils x die Gleichung x = 1− exp[−(tτk)]. Die Verzögerung beruht auf einer Änderung der Konstanten, während der Exponent k vom Druck nicht abhängt. Die aus der Temperaturabhängigkeit von τ gewonnene Aktivierungsenergie der Rekristallisation ist bei beiden Drucken 19,5 ± 1,5 kcal/Mol. Es wird gezeigt, daβ diese Ergebnisse mit dem Bailey-Hirsch-Modell für Rekristallisation übereinstimmen. Auβerdem wird durch den beobachteten Druck-Einfluβ die Möglichkeit ausgeschlossen, daβ die Bildung von Rekristallisationskeimen in stark kaltverformtem Kupfer durch irgendein Modell beschrieben werden kann, dem die Bildung von beweglichen Korngrenzen durch Versetzungsbewegung beim Ausheilen zugrunde liegt.

The Formation of Recrystallization Nuclei

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