Grain boundry phenomenon explains lots of physical things about crystalline materials. Understanding the nature of grain boundries in materials especially in metals, equals to understanding of lots of physical characteristics in certain situations. In this article we will explain the grain boundry structures in crystalline materials and how can we interpret the materials’ situations according to these microstructures.
Grain boundries occur in cooling phase of crystalline material. Each grain boundries have their own crystal orientation. Because of these different orientations, boundries occur between these differently oriented crystal microstructures. Also in grain boundry regions, there can be few amount of atoms that do not belong to neither of crystal orientations in the material. Number of grain boundries in a material depends on the number of nucleation zones that exist. Each nucleation zone in solidification of the material, create a crystal grains. So the number of nucleation zones can be increased artificially to obtain much more grains and grain boundries in material.
Generally these artificial nucleation zones are created by cold walls inside the mold.
To obtain much more bigger grain size which also means lower grain boundries are obtained with faster cooling rate. Also reverse situation can be achieved slower cooling rate.
The smaller grains sizes are preferable in materials engineering. Smaller grain sizes means much more grain boundries in material. When there is a stress application on material, grain boundries prevent the emergence of imperfections in the microstructure, which means much more harder than bigger grained one.
Also smaller grain bounded materials have very good forming capabilities, because these materials are much more ductile to compared with bigger grained ones. Better surface qualities can be obtained with smaller grained materials.
In solidification process, the sub-process called strain hardening is applied to obtain smaller grain sizes in crystalline materials.
The information about Grain Boundries in crystalline materials can be summarized like that.
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