These individual crystals are called"grains." In any one grain, all atoms are arranged with one particular orientation and one particular pattern. These crystal boundaries determine in no small way the useful properties of engineering materials when applied to steam generators.Īll boiler alloys are made up of many crystals of various individual orientations. Where adjacent crystals join is a crystal boundary, a zone of short-range disorder. There is then, long-range atomic order within individual crystals. For our general purposes, atoms within a metallic crystal or grain are regularly arranged over great distances, distances that are huge when compared with atomic dimensions. Metals, like everything else, are made up of atoms, and for explanations used here, are assumed to be solid spheres.
#Grain boundary series
Summary: The following article is a part of National Board Classic Series and it was published in the National Board BULLETIN. French, Inc., Metallurgists, Northborough, MA By performing TEM-EDS point analysis, it is found that in addition to grain size space charge potential at grain boundaries gives higher relative permittivity.President of David N. Relative permittivity increases by increasing grain size. Relative permittivity of densified strontium titanate measured at room temperature at 1 MHz shows very high and it is in between 180 to 268. Grain size dependent relative permittivity, dielectric loss and optical transparency are investigated. Coincident Site lattice (CSL) value of 5 and 19 was dominating in iron oxide system.įinally, both nano and micro crystalline optically transparent strontium titanate are processed. In the second part of the dissertation, grain boundary geometry of iron oxide is investigated by Electron Back Scattered Diffraction (EBSD) method. Nanocrystalline materials have higher grain boundary curvature compare to microcrystalline materials. It is found that the slope of grain boundary curvature is grain size and material dependent. Several different types of materials were chosen, such as, micro and nano crystalline aluminum (Al), silicon (Si) and iron oxide (Fe2O3). In the first part of the dissertation, the effect of grain size on the grain boundary curvature is investigated. There are three different parts in this dissertation: (1) Affect of grain size on grain boundary curvature on different materials for example, nano and micro crystalline aluminum (metallic bond), silicon (covalent bond) and iron oxide (ionic bond) (2) Grain boundary geometry analysis of nanocrystalline materials and (3) Grain size dependent electrical and optical property investigation. X-ray analysis, Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) are used to characterize the materials. Joule heating and pressure are used to densify the materials in CAPAD system. It offers faster processing of nanoscale materials compared to traditional sintering technique. CAPAD is a unique technique for materials processing. In order to study the grain boundaries in different materials, fully dense bulk materials are processed using Current Activated Pressure Assisted Densification (CAPAD) technique. Increased understanding of the role of grain boundaries play in nanocrystalline materials promotes the tunning of materials properties. Nanocrystalline materials have unique properties compared to coarse grain counterpart because of the presence of more grain boundaries. In polycrystalline materials, different properties (mechanical, electrical, optical, magnetic) are affected by the size of their grains and by the atomic structure of their grain boundaries. For example, when grain size is 10 nm grain boundary volume fraction is ~ 25%. When grain size decreases the volume fraction of grain boundaries increases. The total volume of occupied grain boundaries in polycrystalline material depends on the grain size. Polycrystalline materials are composed of grains and grain boundaries.
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