MS115a Lect 14 10 26 2011

MS115a Lect 14 10 26 2011 - Plastic Deformation Permanent...

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Plastic Deformation Permanent, unrecovered mechanical deformation σ  = F/A  stress Deformation by dislocation motion, “glide” or “slip” Dislocations Edge, screw, mixed Defined by Burger’s vector Form loops, can’t terminate except at crystal surface Slip system Glide plane + Burger’s vector maximum shear stress

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Slip system = glide plane + burger’s vector Correspond to close-packed planes + directions Why? Fewest number of broken bonds Cubic close-packed Closest packed planes {1 1 1} 4 independent planes Closest packed directions Face diagonals <1 1 0> 3 per plane (only positive) 12 independent slip systems a 1 a 2 a 3 Crystallography of Slip b = a/2 <1 1 0> | b | = a/ 2 [1 1 0]
HCP “BCC” Planes {0 0 1} 1 independent plane Directions <1 0 0> 3 per plane (only positive) 3 independent slip systems Planes {1 1 0} 6 independent planes Directions <1 1 1> 2 per plane (only positive) 12 independent slip systems b = a <1 0 0> | b | = a b = a/2 <1 1 1> | b | = 3 a/2 Occasionally also {1 1 2} planes in “BCC” are slip planes Diamond structure type: {1 1 1} and <1 1 0> --- same as CCP, but slip less uncommon

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Why does the number of independent slip systems matter?
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MS115a Lect 14 10 26 2011 - Plastic Deformation Permanent...

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