1.01 – Fundamental Properties of Defects in Metals

The review focuses on those fundamental properties of vacancies and self-interstitials in pure metals that govern the microstructural evolution at elevated temperatures during irradiation. The first property for the production of atomic defects is the displacement energy. It is the minimum recoil energy that an atom must receive from the radiation that will produce one Frenkel pair, namely one vacancy and a nearby self-interstitial. This displacement energy is significantly larger than the sum of the vacancy and interstitial formation energies. We present theoretical models for both that explain their magnitude and show that the formation energies depend on the defect relaxation volumes. These latter fundamental parameters also determine the long-range elastic strain fields of atomic defects. The associated elasticity models are briefly reviewed in two appendices. Vacancy migration energies can also be derived from an additional elastic lattice relaxation that accompanies the transition through the saddle point configuration; two successful models by Flynn and by Kornblit are evaluated and compared with experimental data. Next, we consider the long-range elastic interactions of atomic defects with the strain fields originating from external loads or from other lattice imperfections. Three major interactions are discussed in detail, namely the misfit or size interaction, the diaelastic or modulus interaction, and the image interaction near free surfaces. When these interactions arise from nonuniform strain fields, diffusion for atomic defects becomes anisotropic as well as directed by drift forces. In turn, these drift forces give rise to different capture rates for self-interstitials and for vacancies, and this difference can be expressed in the form of so-called bias factors. They are key parameters for rate theories and responsible for the continuing evolution of the microstructures in irradiated metals. We present bias factors for edge dislocations and voids. Finally, the thermal emission rate of vacancies from these defect sinks depends on the vacancy concentration in local thermodynamic equilibrium, and we provide expressions for it near edge dislocations, prismatic dislocation loops, and near voids and bubbles.