ABSTRACT
Structural imperfections have a strong influence on physical and mechanical properties of metals as well as on the evolution of phase transformations in metallic materials. Imperfections can be classified according to dimension: point defects, such as vacancies and interstitials; linear imperfections, such as edge and screw dislocations; surface imperfections, such as grain boundaries and interfaces; and three-dimensional defects, such as voids and inclusions. The defects play a key role in the mechanical behavior of metals and the development of microstructure through phase transformations. The primary interfaces in the microstructure of metals and alloys are: free surfaces of crystals; grain boundaries; interphase boundaries (boundaries between phases); and stacking faults. At each temperature there exists a certain concentration of point defects at thermodynamic equilibrium in the crystal. The concentration of vacancies and interstitials increases exponentially with temperature, following Arrhenius-type temperature dependence. The concentration of interstitials is several orders of magnitude lower than the concentration of vacancies at the same temperature.
