L5- Dislocation interactions + partial dislocations

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9 Terms

1
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Cross slip

  • The movement of a dislocation from one glide plane to another

  • Line vector and Burgers vector must be common to both planes

  • Edge dislocation can’t cross slip only screw dislocation can.

  • For a mixed dislocation to cross slip it must straighten to a pure screw type.

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Why can perfect dislocation dissociate into 2 so-called partial dislocations

an fcc dislocation is composed of two extra half planes

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Why will partials repel each other?

  • They are of the same type + similar line sense

  • forms stacking fault + requires energy

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Effect of stacking fault energy on hardening

  • cross-slip of partials = hardest with low stacking fault energy

  • as partials = most widely separated in this material

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Stacking fault energy

Energy required to create a defect in the stacking sequence of atoms in a crystalline material

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Lomer-Cottrell lock

  • produces a dislocation out of slip plane + is sessile→ i.e. stair rod dislocations

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Peierls stress

The stress required to move a dislocation through a perfect crystal at 0k.

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Eqn for Peierls stress

  • w = width of dislocation

  • b = burgers vector

  • G = shear modulus

  • ν = poissons ratio

<ul><li><p>w = width of dislocation </p></li><li><p>b = burgers vector </p></li><li><p>G = shear modulus </p></li><li><p><span>ν = poissons ratio</span></p></li></ul>
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Consequence of Peierls stress

  • Dislocations with wide slip plane move more easily

  • OR smaller burgers vector