Crystal Defects

This chapter focuses on dislocation theory and inherently developed crystal defects that disrupt or dislocate the regular geometrical arrangement of atoms in crystalline solids. Essentially, crystal defects are imperfections or discontinuities that govern material properties. The most common atomic discontinuities in engineering polycrystalline materials are the grain boundaries, shrinkage pores due to the formation of gas bubbles during solidification, flaws and possibly inclusions in steels, such as brittle ceramic phases known as metal oxides (FeO, \(Al_{2}O_{3}\) ), metal sulfates (MnS, \(Al_{2}S_{3}\) , \(Cr_{2}S_{3}\) ), and chromite (MnO- \(Cr_{2}O_{3}\) ). Thus, the most relevant inherent defects are point defects due to missing atoms in the lattice, linear defects called dislocations that consist of groups of atoms in irregular positions, and planar defects, such as grain boundaries, and stacking faults (SFs) are interfaces separating homogeneous and adjacent crystal grains or particles in solids. The goal in this chapter is to characterize crystal defects in metallic and nonmetallic crystals at an atomic scale. Crystals or crystalline solids have a long-range order (regular arrangement of atoms). Amorphous solids, on the other hand, have a short-range order.