Day16 - Module#16 Module#16 Jogs Kinks and Dislocation Intersections Kinks and Dislocation Intersections SUGGESTED READING Hull Bacon pp 52-57 Bacon pp

Day16 - Module#16 Module#16 Jogs Kinks and Dislocation...

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Module #16 Jogs Kinks and Dislocation Intersections Jogs, Kinks, and Dislocation Intersections SUGGESTED READING* Hull & Bacon pp 52-57 Hull & Bacon, pp. 52-57 * Thi li d h d d ll f h h I h b bl d Prof. M.L. Weaver This list does not mean that you need to read all of these chapters. It has been assembled to provide you with suggested reading from that you may be using OR referring to in your course. Most of these chapters cover similar material. Any “required” reading will be noted separately.
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RECALL dislocations move via Glide (conservative motion): moves on a surface that contains both its line and Burgers vector. – A that moves this way is glissile. – A that can’t move is sessile. glide surface and direction depend upon crystal structure. Climb (non-conservative motion) moves out of the glide surface, perpendicular to the Burgers vector. Prof. M.L. Weaver
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Dislocation motion via “glide” / “slip” Screw moves EDGE x y G Edge moves thi this way τ yx τ yx E F H τ yx τ yx this way Schematic illustration of single crystal deformation via motion of a screw dislocation. (a) Application of a shear stress τ yx can introduce a screw dislocation into a crystal along line EF and (a) (b) x y τ yx τ yx B D z cause it to move to position HG . (b) Lattice presentation clearly showing that the dislocation has right-hand screw character. Adapted from S.M. Allen and E.L. Thomas; The Structure of Metals ; Wiley, New York, (1998) p. 285 (a) (b) z τ yx τ yx A C SCREW Schematic illustration of single crystal deformation by motion of an edge dislocation. (a) Application of shear stress τ yx can introduce an edge dislocation into a crystal along AB and cause it to move to position DC . (b) Lattice representation Prof. M.L. Weaver clearly showing that the dislocation has edge character. Adapted from S.M. Allen and E.L. Thomas; The Structure of Metals ; Wiley, New York, (1998) p. 284
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Process of slip by expansion of a dislocation l li l (1) loop on a slip plane. Dislocation line b b (2) b Dislocation line b $ b b (3) •Edge, screw, and mixed Edge, screw, and mixed segments move. •Final shear of crystal is b b Prof. M.L. Weaver produced by edge and screw dislocations.
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Ed di l ti Edge dislocations are restricted to slip on a specific slip plane. x y D F τ yx A B C E z τ yx b Slip plane is AEFB Prof. M.L. Weaver
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Slip Cross-Slip Cross-slip plane b b Slip plane Screw dislocations are not restricted to Primary slip plane Prof. M.L. Weaver a single plane. They can cross-slip Edge dislocations cannot
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Dislocation Glide Dislocations glide at glide velocities ( v ). Depend on: Applied stress; Purity of the crystal; – Temperature; Type of dislocation. Johnston and Gilman showed that the dislocations in ionic crystals would begin glide at the critical resolved ionic crystals would begin glide at the critical resolved shear stress : m A This equation is empirical in nature Where is the applied shear stress in the slip plane, is o v and applies for a specific velocity range: 10 -9 to 10 -3 m/s Prof. M.L. Weaver Where is the applied shear stress in the slip plane, o is
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