Papers by Keyword: Nucleation

Abstract: In this work, EBSD (Electron Back Scattered Diffraction) measurements have been performed on deformed, partially and fully recrystallized cold rolled copper to 70 and 90 % reduction. The twin fraction as well as its existing relation with the parent crystallographic orientation has been followed in relation with respect to the recrystallized fraction. It has been shown thanks to this quantitative analysis that annealing twinning is more active when recrystallization nuclei slowly develop. The experimental observations are briefly discussed according with the twins selection principles [1].

Abstract: A critical point in the understanding of recrystallization textures is the development of crystallographic orientations of the nuclei. Here an issue, which has been debated much recently [eg. 1], is if nuclei have orientations identical to those of the deformation microstructures from which they originate or not. Traditional nucleation mechanisms like strain induced boundary migration [2] and particle stimulated nucleation [3] operate with nuclei orientations identical to the “parent”deformation microstructure. This is also what is commonly incorporated in recrystallization modeling. However, a number of studies have found recrystallization nuclei in orientations that were not expected from measurements on deformed structures. Some of these results are reviewed and discussed in this paper, and new in-situ results obtained by the 3 dimensional X-ray diffraction (3DXR) method are presented.

Abstract: An experimental setup was designed to study the recrystallization kinetics of Interstitial Free (IF) steel in this work. The 80% cold rolled IF steel foils are heated rapidly to 680°C, 730°C and 780°C by a salt bath. The recrystallization kinetic curves were obtained by the quantitative analysis of texture components, microstructures and EBSP (electron back-scattering patterns) measurements. With the help of EBSD, the orientations of the recrystallization nuclei are determined. The growth rule of the recrystallization nuclei was analyzed statistically. The effect of nucleus orientation on the formation of the recrystallization texture was investigated.

Abstract: The recrystallization process of two low-carbon ferritic steels with low fraction of alloying elements are modelled. The difference in chemical composition and initial thermomechanical treatment between these two steels can be the cause of the difference in the stored energy distribution after 40% deformation by cold rolling or plane compression simulated by Finite Element Modelling (FEM). In both cases the deformation texture is characterized by the presence of a g- fibre with a reinforcement for the {111}<112> component. The microstructure simulated by FEM is used as initial structure for Monte-Carlo simulations of recrystallization. In these simulations, the variation in chemical composition and initial thermo-mechanical treatment is introduced by the difference in stored energy distribution while recovery, nucleation and grain growth are simulated assuming that grain boundary properties mainly depend on misorientation. Modelling results are in agreement with experimental observations: that is the presence of a g- recrystallization fibre which corresponds to the initial deformed state and the development of {111}<110> component which is not sharp in the deformation microstructure.

Abstract: NaX zeolite crystals of 50 µm were grown by a continuous crystallization with seed crystal (10 ㎛) in a mother solution having a 3.5Na2O : Al2O3 : 2.1SiO2 : 1000H2O composition. The seed crystal morphology of NaX zeolite shows that an octahedron is formed composed of 8 equilateral triangles which have an average lattice constant of a = 24.9911 Å with a SiO2/Al2O3 molar ratio of 2.1~2.4. In order to grow crystals of zeolite X to an appropriate size by the continuous method, the mother solution was supplied with various seed contents (3~20 wt%) in an autoclave at 90°C after 7, 12, 16, 19 and 24 days.

Abstract: The problem with zeolite crystals synthesized by conventional methods is that they are extremely small: their size typically varies 2 and 8 µm, To better define the structure of a zeolite, scientists need to grow crystal that are 100 to 1000 times larger. In this work, large crystals zeolite NaX with a uniform size of 50µm were grown by a continuous crystallization method from seed crystals (5-10µm) formed in a mother solution with the 3.5Na2O : Al2O3 : 2.1SiO2 : 1000H2O composition. In order to grow zeolite NaX crystals to an appropriate size by the continuous method, the mother solution was fed into an autoclave a solution with various seed contents (3 - 20wt%); the autoclave has at 90°C and the solution was added after 7, 12, 16, 19 and 24 days or at 100°C after 7 and 9 days.

Abstract: Thick (111) oriented β-SiC layers have been grown by hetero-epitaxy on a (0001) a-SiC substrate with the Continuous Feed-Physical Vapour Transport (CF-PVT) method. The growth rate was 68 µm/h at a pressure of 2 torr and a temperature of 1950°C. The nucleation step of the β-SiC layer during the heating up of the process was studied in order to manage first the a to b heteropolytypic transition and second the selection of the b-SiC orientation. With a adapted seeding stage, we grew a 0.4mm thick layer almost free of Double Positioning Boundaries on a 30mm diameter sample. First observations of the layer by cross-polarised optical Microscopy are presented both in planar view and in cross section geometry.

Abstract: The influence of the different additions to the melt on the nucleation behavior during short time flash lamp processing was investigated. It was observed that germanium and carbon additions to the silicone melt led to an increase of the mass transport to the growing surface and to an increase of the nuclei size. In the case of germanium additions to the silicon melt an incorporation of germanium in the silicon substrate was observed.