Recrystallization and Grain Growth

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Authors: Nathalie Bozzolo, N. Dewobroto, Thierry Grosdidier, Pierre Barbéris, Francis Wagner
Abstract: Primary recrystallization of a 80% cold–rolled T40 or Zr702 sheets leads to equiaxed microstructures. Subsequently, only normal grain growth takes place in T40 while a few grains can grow abnormally after sufficient time at high annealing temperature (close to the transus) in Zr702. The grain sizes reached after extended grain growth at moderate temperatures in Zr702 are smaller than in T40. The presence of precipitates in Zr702 is probably responsible for this and also for the abnormal phenomena observed at high temperature in this material. The texture changes occurring in both materials under normal grain growth conditions (often roughly described as “30° rotation around c axes”) are due to the development of the largest grains produced by the primary recrystallization. These large grains are preferentially oriented around {j1=0°, F=30°, j2=30°} for T40 and around {j1=0°, F=25°, j2=30°} for Zr702, orientations which become predominant after extended grain growth.
441
Authors: Masahiko Demura, Kyosuke Kishida, Ya Xu, Toshiyuki Hirano
Abstract: The texture evolution of 83% cold-rolled Ni3Al foils during recrystallization was examined through heat treatments at 600 °C, 800 °C, and 1000 °C for 30 min. X-ray texture measurements revealed that the texture changed from the as-rolled Goss to a transitional complicated one by primary recrystallization and eventually returned to the Goss texture during grain growth. The SEM-EBSD analysis revealed that the return to the Goss texture was accompanied by the decrease of random boundaries (RBs) and the increase of S1 boundaries. The preferential growth of the Goss-oriented grains was explained by the difference in the grain boundary energy between the RBs and S1, based on the observed grain-orientation maps.
447
Authors: N. Dewobroto, Nathalie Bozzolo, Pierre Barbéris, Francis Wagner
Abstract: The microstructure and crystallographic texture in zirconium (Zr702) sheets, initially deformed by 80% cold rolling, are investigated at different stages of the primary recrystallization. Inhomogeneities were observed in the deformed microstructure at different scales down to the submicrometer range. The influence of these inhomogeneities on the local recrystallization mechanisms is discussed. The measurement of the orientation of the new grains shows that the nucleation is definitely not oriented. Since the global texture change is very slight, recrystallization by subgrain growth is probably one of the most important mechanism during the recrystallization process in zirconium.
453
Authors: F.M. Güçlü, H. Çimenoğlu
Abstract: In the present investigation, recrystallization of Grade-2 quality commercial purity titanium (CP-Ti) has been studied. CP-Ti was received as 4 mm thick plate having hardness of 202 HV0.3. Upon rolling about 55, 70 and 85 % at room temperature, the hardness increased to 268, 276 and 283 HV0.3, respectively. Cold rolled samples were then subjected to isothermal annealing in salt bath at 550-700°C. After measuring hardness, recrystallization curves were plotted for each annealing temperature. Recovery region was not clearly visible on the recrystallization curves. Heavily cold worked samples were soften rapidly and reached to the grain growth region at shorter annealing times. According to Arrhenius plot, recrystallization activation energy of CP-Ti was calculated in between 89,5 and 78,6 kJ/mol. The higher the cold working, the lower is the recrystallization activation energy.
459
Authors: W. Bevis Hutchinson, James Oliver, Margareta Nylén, Joacim Hagström
Abstract: Conditions favouring spontaneous growth of whiskers from tin coatings are discussed. Observations are reported concerning orientations and geometry of whiskers. The driving force for growth arises from elastic stress in the coating and can be expressed as a Gibbs free energy in terms of the decrease in pressure. An analysis of diffusion-controlled growth based on grain boundary diffusion seems to be capable of accounting for the fast growth kinetics that are observed in practice at room temperature.
465
Authors: S. Jakani, Marie Helene Mathon, Ph. Gerber, Mustafa Benyoucef, C.-H. De Novion, Thierry Baudin
Abstract: Cold-drawn Electrolytic Tough Pitch copper wires have been investigated with Neutron Diffraction and Electron Back Scattered Diffraction. The drawn copper wires (38% reduction in area) develop major <111> and minor <001> fiber textures. It appears that the texture intensity of the reinforcements within the <111> and <001> fibers is more pronounced in the center and intermediate part of the wires. During the first annealing time, it is found that the recrystallization kinetics is enhanced when oxygen content is increased. The recrystallized fraction within the intermediate zone of the wire is two times larger in the cathode with higher oxygen content. The mechanisms at the origin of this acceleration of recrystallization kinetics will be discussed taking into account the presence of Cu2O type oxides.
471
Authors: L.W.F. Mackenzie, Gordon W. Lorimer, John F. Humphreys, T. Wilks
Abstract: The deformation and recrystallization behaviour of two magnesium alloys, WE43 and an experimental “Alloy A1” containing a large amount of second phase, have been investigated. Optical microscopy and electron backscattered diffraction (EBSD) were used to observe each alloy after deformation in a channel die at 553 and 558 K and subsequent recrystallization during annealing at 673 K. Alloy A1 dynamically recrystallised during deformation at 553 and 558 K. In WE43 the particle distribution affected the onset of dynamic recrystallization. Both alloys exhibited evidence of particle stimulated nucleation (PSN) of recrystallization at second phase particles as well as recrystallization at pre-existing grain boundaries. The A1 and WE43 alloys were extruded at temperatures of 573 K and 633 and 663 K, respectively. The extruded microstructures were compared to those that developed during channel die deformation.
477
Authors: Dmitri A. Molodov, A.D. Sheikh-Ali
Abstract: The annealing of cold rolled (82%) titanium sheet at 750°C in a magnetic field of 19.4 Tesla results in a distinct difference between texture peaks when the sample is tilted by +30° or -30° to the field direction around the rolling direction, i.e. c (<0001>)-axis of grains corresponding to one texture component is aligned normal to the field direction. This result is attributed to grain growth affected by an additional driving force arising in a magnetic field by the anisotropy of the magnetic susceptibility of titanium.
483
Authors: Sergey A. Nikulin, A.B. Rojnov, M.M. Peregud
Abstract: Using transmission electron microscopy, x – ray diffraction analysis, tensile testing and fractography the changes were analyzed that occur in microstructure and tensile properties of E635 alloy annealed after quenching from b – region of phase diagram. The interrelation is demonstrated between microstructure and tensile properties depending on deformation/heat treatment conditions.
489
Authors: I. Hünsche, C.G. Oertel, R. Tamm, Werner Skrotzki, W. Knabl
Abstract: Recrystallization is an important tool to adjust the grain size and texture of polycrystalline materials in order to optimize their properties. In the present work recrystallization and the related changes of texture have been studied on rolled molybdenum sheets as a function of temperature and time. The microstructure was investigated by orientation contrast in a scanning electron microscope. The kinetics of recrystallization displayed in a JMAK plot yields Avrami coefficients decreasing with temperature from 2.5 to 1.1. The activation energy amounts to 5 eV, which agrees well with the volume self-diffusion coefficient. The textures of the sheet surface and central layer were measured by X-ray diffraction. The rolling texture in the centre of the sheets is characterized by a strong a-fibre with the rotated cube component {100}<110> dominating. Besides that, there exists a weak g-fibre. In contrast, the surface layer is characterized by a weak cube component. During recrystallization changes in texture are insignificant. With long annealing times all texture components tend to degrade. Conclusions regarding the deep-drawability are drawn.
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