IMPERFECTIONS IN METALSDOE-HDBK-1017/1-93Structure of MetalsThe slip occurs when the crystal is subjected to a stress, and the dislocation movesthrough the crystal until it reaches the edge or is arrested by another dislocation, asshown in Figure 9. Position 1 shows a normal crystal structure. Position 2 shows a forceapplied from the left side and a counterforce applied from the right side. Positions 3 to5 show how the structure is slipping. Position 6 shows the final deformed crystalstructure. The slip of one active plane is ordinarily on the order of 1000 atomicdistances and, to produce yielding, slip on many planes is required. Screw dislocations can be produced by a tearing of the crystal parallel to the slipFigure 9 Slipsdirection. If a screw dislocation is followed all the way around a complete circuit, itwould show a slip pattern similar to that of a screw thread. The pattern may be eitherleft or right handed. This requires that some of the atomic bonds are re-formedcontinuously so that the crystal has almost the same form after yielding that it hadbefore.The orientation of dislocations may vary from pure edge to pure screw. At someintermediate point, they may possess both edge and screw characteristics. Theimportance of dislocations is based on the ease at which they can move through crystals.MS-01Page 20Rev. 0
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