Module #16Jogs Kinks and Dislocation IntersectionsJogs, Kinks, and Dislocation IntersectionsSUGGESTED READING*•Hull & Bacon pp 52-57Hull & Bacon, pp. 52-57*Thilidhddllf hhI hbbl dProf. M.L. WeaverThis list does not mean that you need to read all of these chapters.It has been assembled toprovide 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.
RECALLdislocations 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
Dislocation motion via “glide” / “slip”Screw moves EDGExyGEdge moves thithis wayτyxτyxEFHτyxτyxthis waySchematic illustration of single crystal deformation via motion of a screw dislocation. (a) Application of a shear stress τyxcan introduce a screw dislocation into a crystal along line EFand (a)(b)xyτyxτyxBDzcause 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)zτyxτyxACSCREWSchematic illustration of single crystal deformation by motion of an edge dislocation. (a) Application of shear stress τyxcan introduce an edge dislocation into a crystal along AB and cause it to move to position DC. (b) Lattice representation Prof. M.L. Weaverclearly 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
Process of slip by expansion of a dislocation llil(1)loop on a slip plane.Dislocation linebb(2)bDislocation lineb$bb(3)•Edge, screw, and mixedEdge, screw, and mixed segments move.•Final shear of crystal is bbProf. M.L. Weaverproduced by edge and screw dislocations.
Eddi ltiEdge dislocations are restricted to slip on a specific slip plane.xyDFτyxABCEzτyxbSlip plane is AEFBProf. M.L. Weaver
SlipCross-SlipCross-slip planebbSlip planeScrew dislocations are not restricted toPrimary slip planeProf. M.L. Weavera single plane. They can cross-slipEdge dislocations cannot
Dislocation Glide•Dislocationsglide atglidevelocities(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 thecritical resolvedionic crystals would begin glide at the critical resolved shear stress:mAThis equation is empirical in nature •Whereis the applied shear stress in the slip plane,isovand applies for a specific velocity range: 10-9to 10-3m/sProf. M.L. WeaverWhere is the applied shear stress in the slip plane, ois