Solidification Microstructures

In the example given above, the formation of a material microstructure was seen to take place as a result of the deposition of atoms on a substrate. Another, equally important, route to solid microstructures is via the solidification process. During the solidification process, the baseline microstructure, which will have a significant impact on both the material s properties as well as its subsequent microstructural evolution, is created as the liquid is superseded by a solid. The nature of the microstructure in the resulting solid can be quite diverse, ranging from featureless equiaxed polycrystals, to microstructures riddled with dendrites. 

The conceptual features of the model are illustrated in fig. 12.18. The basic idea is the simultaneous use of two computational meshes to treat the same overall spatial domain. As shown in the top frame of fig. 12.18, a finite element mesh 

Phase Field Approaches to Solidification. The phase field approach has found favor not only in the types of mixed models mentioned above but also in the solidification context. Though we haven t made much of this point, one of the key advantages of the phase field approach is that it obviates the need of explicitly tracking any interfaces during the course of a simulation since all that is really monitored is one or more field variables throughout space. There are two key field 

An example of the type of results that can be achieved with this approach is shown in fig. 12.20, which cleverly depicts four distinct features associated with the solution of a dendrite structure with fourfold symmetry. The upper left hand panel of the figure shows the nonuniform finite element mesh used in the solution of the governing equations. Contours of constant temperature are shown in the 

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M. D. Dupouy, B. Drevet, D. Camel. Influence of convection on the selection of solidification microstructures at low growth rates. J Crys Growth 181 45, 1997. 

To fulfill these requirements, the experiments were carried out on small ingots (35 g) solidified in a ceramic crucible at a preset, controlled cooling rate. The development of the solidification microstructure is governed mainly by alloy composition and the rate of heat removal. By using samples of commercial alloys and letting them cool at a rate similar to that found in full scale Ingots, good reproduction of microstructural features was obtained. 

In short, there is little research related to the study of mechanical and electrochemical properties of Zn-Al alloys as well as Zn-Al alloys MMCs containing SiC and AI2Q3 particulations with different grain structures in the matrix. Also there is lack of fundamental study on the performance of Zn-Al alloys and their MMCs in corrosive environments when both solidification microstructure and type of particle distribution are in consideration. In the present research, Zn-Al-SiC and Zn-Al-AI2O3 composites are prepared and solidified by vertical directional solidification method. By means of voltammograms and electrochemical impedance spectroscopy, the corrosion resistances of Zn-Al matrix composite materials with different types of particles are obtained and analyzed and the results are compared. 

Nuri et al. (1982) reported on the characteristics of rare-earth-added steels, especially the solidification microstructure (including the spacing, length and inclination of dendrite arms) and microsegregation with some consideration of the relevant mechanisms. Microstructural observations revealed that in the rare-earth-added steel fine-grained dendrites at the surface develop extensively, with the adjoining columnar dendrites growing less than those in rare-earth-ffee steel. This difference in the solidification structure has an effect on the secondary structure after solidification. 

Systems Zr02-Ln203 [Ln=Lanthanide) Unidirectional Solidification, Microstructural and Crystallographic Characterization. 0. Mat. Sci. 15 61-66 (1980). ... 

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