Creating and destroying vacancies in solids and nonequilibrium grain boundary segregation

How the vacancies in excess of equilibrium concentration are created and destroyed in solids is crucial for understanding many of their physical characteristics and processes. Grain boundaries are known as sources and sinks for bulk vacancies, but what exchange will occur between the grain boundary and the bulk under a stress is still obscure. In the present paper, we show that grain boundaries will work as sources to emit vacancies when a compressive stress is exerted on them and as sinks to absorb vacancies when a tensile stress is exerted. This is the sixth method of introducing and annihilating vacancies in solids in addition to the five methods mentioned in literature. At the same time, this physical process will produce solute nonequilibrium grain-boundary segregation/dilution. A set of kinetic equations is established to describe such a physical process. Additionally an attempt has been made to simulate Misra's experimental data with the kinetic equations to justify the physical process.