222-227 Crystal Defects - IMPERFECTIONS IN SOLIDS (DEFECTS)...

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1 Chapter 4 - IMPERFECTIONS IN SOLIDS ( DEFECTS )
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2 Chapter 4 - Vacancy atoms Interstitial atoms Substitutional atoms Point defects Types of Imperfections Dislocations Line defects Grain Boundaries Area defects Cracks, voids etc Bulk defects
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3 Chapter 4 - POINT DEFECTS
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4 Chapter 4 -
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5 Chapter 4 - Vacancies : -vacant atomic sites in a structure. Self-Interstitials : -"extra" atoms positioned between atomic sites. Point Defects Vacancy distortion of planes self- interstitial distortion of planes
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6 Chapter 4 - Boltzmann's constant N v N = exp - Q v k T No. of defects No. of potential defect sites. Activation energy Temperature Equilibrium concentration varies with temperature! VACANCY CONCENTRATION
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7 Chapter 4 - Diffusion Mass transport by atomic motion
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8 Chapter 4 - Interdiffusion : In an alloy, atoms tend to migrate from regions of high conc. to regions of low conc. Initially Adapted from Figs. 5.1 and 5.2, Callister 7e . Diffusion After some time
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9 Chapter 4 - Self-diffusion : In an elemental solid, atoms also migrate. Label some atoms After some time Diffusion A B C D A B C D
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10 Chapter 4 - Diffusion Mechanisms Vacancy Diffusion: atoms exchange with vacancies applies to substitutional impurities atoms rate depends on: --number of vacancies --activation energy to exchange. increasing elapsed time
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11 Chapter 4 - Diffusion Mechanisms Interstitial diffusion – smaller atoms can diffuse between atoms. More rapid than vacancy diffusion Adapted from Fig. 5.3 (b), Callister 7e .
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Chapter 4 - Adapted from chapter-opening photograph, Chapter 5, Callister 7e. (Courtesy of Surface Division, Midland-Ross.) Case Hardening : --Diffuse carbon atoms into the host iron atoms at the surface. --Example of interstitial
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This note was uploaded on 09/25/2011 for the course METE 227 taught by Professor Ali during the Spring '10 term at Middle East Technical University.

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222-227 Crystal Defects - IMPERFECTIONS IN SOLIDS (DEFECTS)...

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