IMPERFECTIONS IN METALSDOE-HDBK-1017/1-93Structure of MetalsIMPERFECTIONS IN METALSThe discussion of order in microstructures in the previous chapters assumedidealized microstructures. In reality, materials are not composed of perfectcrystals, nor are they free of impurities that alter their properties. Evenamorphous solids have imperfections and impurities that change their structure.EO 1.13IDENTIFY the three types of microscopic imperfections foundin crystalline structures.EO 1.14STATE how slip occurs in crystals.EO 1.15IDENTIFY the four types of bulk defects.Microscopic imperfections are generally classified as either point, line, or interfacialimperfections.1.Point imperfections have atomic dimensions.2.Line imperfections or dislocations are generally many atoms in length.3.Interfacial imperfections are larger than line defects and occur over a two-dimensional area.Point imperfections in crystals can be divided into three main defect categories. Theyare illustrated in Figure 7.1.Vacancy defects result from a missing atom in a lattice position. Thevacancy type of defect can result from imperfect packing during thecrystallization process, or it may be due to increased thermal vibrationsof the atoms brought about by elevated temperature.2.Substitutional defects result from an impurity present at a lattice position.3.Interstitial defects result from an impurity located at an interstitial site orone of the lattice atoms being in an interstitial position instead of beingat its lattice position. Interstitial refers to locations between atoms in alattice structure.MS-01Page 18Rev. 0
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