Figure 9 Slips

IMPERFECTIONS IN METALS DOE-HDBK-1017/1-93 Structure of Metals The slip occurs when the crystal is subjected to a stress, and the dislocation moves through the crystal until it reaches the edge or is arrested by another dislocation, as shown in Figure 9. Position 1 shows a normal crystal structure. Position 2 shows a force applied from the left side and a counterforce applied from the right side. Positions 3 to 5 show how the structure is slipping. Position 6 shows the final deformed crystal structure. The slip of one active plane is ordinarily on the order of 1000 atomic distances and, to produce yielding, slip on many planes is required. Screw dislocations can be produced by a tearing of the crystal parallel to the slip Figure 9 Slips direction. If a screw dislocation is followed all the way around a complete circuit, it would show a slip pattern similar to that of a screw thread. The pattern may be either left or right handed. This requires that some of the atomic bonds are re-formed continuously so that the crystal has almost the same form after yielding that it had before. The orientation of dislocations may vary from pure edge to pure screw. At some intermediate point, they may possess both edge and screw characteristics. The importance of dislocations is based on the ease at which they can move through crystals. MS-01 Page 20 Rev. 0