Structure of MetalsDOE-HDBK-1017/1-93IMPERFECTIONS IN METALSInterstitial impurities called network modifiers act as point defects inamorphous solids. The presence of point defects can enhance or lessenthe value of a material for engineering construction depending upon theintended use.Figure 7 Point DefectsFigure 8 Line Defects (Dislocations)Line imperfections are called dislocationsand occur in crystalline materials only.Dislocations can be an edge type, screwtype, or mixed type, depending on howthey distort the lattice, as shown inFigure 8. It is important to note thatdislocations cannot end inside a crystal.They must end at a crystal edge or otherdislocation, or they must close back onthemselves.Edge dislocations consist of an extra rowor plane of atoms in the crystal structure.The imperfection may extend in a straightline all the way through the crystal or itmay follow an irregular path. It mayalso be short, extending only a smalldistance into the crystal causing a slip ofone atomic distance along the glide plane(direction the edge imperfection ismoving).Rev. 0Page 19MS-01
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business