Imperfections in Metals Summary

IMPERFECTIONS IN METALS DOE-HDBK-1017/1-93 Structure of Metals The important information in this chapter is summarized below. Microscopic Imperfections Point imperfections are in the size range of individual atoms. Line (dislocation) imperfections are generally many atoms in length. Line imperfections can be of the edge type, screw type, or mixed type, depending on lattice distortion. Line imperfections cannot end inside a crystal; they must end at crystal edge or other dislocation, or close back on themselves. Interfacial imperfections are larger than line imperfections and occur over a two dimensional area. Interfacial imperfections exist at free surfaces, domain boundaries, grain boundaries, or interphase boundaries. Slip occurs when a crystal is subjected to stress and the dislocations march through the crystal until they reach the edge or are arrested by another dislocation. Macroscopic Defects Bulk defects are three dimensional defects. Foreign particles included in the prime material (inclusions) are most common bulk defect Gas pockets Shrinking cavities Welding or joining defects MS-01 Page 22 Rev. 0