Imperfections in solids_miscellaneous imperfections and microscopic examination

Imperfections in solids_miscellaneous imperfections and microscopic examination

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Materials Science and Engineering MIME 1650 Lecture 8 1 1 Chapter 4 - • Vacancy atoms • Interstitial atoms • Substitutional atoms Point defects Types of Imperfections • Dislocations Line defects • Grain Boundaries Area defects 2 Chapter 4 - Imperfections in Solids • Specification of composition – weight percent 100 x 2 1 1 1 m m m C + = m 1 = mass of component 1 100 x 2 1 1 ' 1 m m m n n n C + = n m1 = number of moles of component 1 – atom percent
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Materials Science and Engineering MIME 1650 Lecture 8 2 3 Chapter 4 - In class problem (4.10) What is the composition, in atom percent, of an alloy that contains 33 g copper and 47 g zinc 4 Chapter 4 - • are line defects, • slip between crystal planes result when dislocations move, • produce permanent (plastic) deformation. Dislocations : Schematic of Zinc (HCP): • before deformation • after tensile elongation slip steps Line Defects Adapted from Fig. 7.8, Callister 7e.
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Materials Science and Engineering MIME 1650 Lecture 8 3 5 Chapter 4 - Imperfections in Solids Linear Defects ( Dislocations ) – Are one-dimensional defects around which atoms are misaligned • Edge dislocation: – extra half-plane of atoms inserted in a crystal structure b to dislocation line • Screw dislocation: – spiral planar ramp resulting from shear deformation b || to dislocation line Burger’s vector, b : measure of lattice distortion 6 Chapter 4 - Imperfections in Solids Fig. 4.3, Callister 7e. Edge Dislocation
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Materials Science and Engineering MIME 1650 Lecture 8 4 7 Chapter 4 - Edge Dislocation Insertion of an extra plane of atoms Dislocation line – defined along edge of half plane Localized lattice distortion around dislocation line Designation or 8 Chapter 4 - Edge Dislocation • Do not think of an edge dislocation as caused by inserting a plane • Causes: – “Accidental” crystal growth by perhaps an
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Imperfections in solids_miscellaneous imperfections and microscopic examination

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