DEFECTS IN CRYSTALS

DEFECTS IN CRYSTALS - Defects in Crystals Chapter 4...

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Defects in Crystals Chapter 4
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Imperfections Most atoms are in ideal locations Small number are out of place Point Defects Line Defects Surface Defects Dominate the material properties
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Strength of a Material Based on the bond strength most materials should be much stronger than they are From Chapter one we know that the strength for an ionic bond should be about 10 6 psi More typical strength is 40*10 3 psi Why? Materials must not usually fail by breaking bonds!!
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Dislocations Line imperfections in a 3D lattice Edge Screw Mixed
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Deformation Deformation of materials occurs when a line defect (dislocation) moves through the material Be sure to watch the video from the text
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Edge Dislocation Extra plane of atoms See the animations in the text Burgers vector Deformation direction For edge dislocations it is perpendicular to the dislocation line
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Screw Dislocation A ramped step Burgers vector Direction of the displacement of the atoms For a screw dislocation it is parallel to the line of the dislocation Harder to visualize than edge dislocations
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Deformation When a shear force is applied to a material, the dislocations move Do the “paper clip” experiment Real materials have lots of dislocations, therefore the strength of the material depends on the force required to make the dislocation move, not the bonding energy
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What happens when a dislocation runs into a flaw? Takes more energy to move “over the
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DEFECTS IN CRYSTALS - Defects in Crystals Chapter 4...

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