MCE 230_F10_ lec_11 - direction • Anisotropy in...

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MCE 230 Materials Science Fall 2010 Lecture - 11
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Crystalline Structure
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Linear density (LD): Linear Density Planner density (PD) Planner Density
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When atomic arrangement is repeated in a perfect way throughout the entire sample All unit cells interlock in the same way and have same orientation Single crystals exist in nature and can be produced ( the environment has to be carefully controlled) Application in electronics microcircuits: single crystals of silicon Single Crystals diamond single crystals for abrasives --turbine blades
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When it is composed of a collection of many small crystals ( or grains) The crystallographic orientations of these crystals (grains) are random When two grains meet; there is a some atomic mismatch (grain boundary) Polycrystalline Materials Grain boundary
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Anisotropy: variation of measured properties with direction Isotropic: when a property is independent of the
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Unformatted text preview: direction • Anisotropy in crystalline materials is a function of the symmetry of the crystal structure ( less symmetry ------ more anisotropy) • Usually the magnitude of a measured property represents an average of directional values Anisotropy Noncrystalline (amorphous) Solids:  The atoms are not systematically and regularly arranged. Noncrystalline Crystalline Noncrystalline (amorphous) Solids:  Whether a solid is crystalline or amorphous depends how the random structure in liquid state can transform to a n ordered state during solidification.  Rapid cooling (during solidification) increase the possibly of noncrystalline formations (little time is allowed for the atoms for ordering process).  Metals-----normally----------crystalline  Ceramic-----------------------crystalline & amorphous  Polymers----normally--------noncrystalline or semicrystalline...
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