Calculation of vacancy concentration under thermo-mechanical loading

The evolution of vacancy system and pore emergence under the influence of cyclic thermo-mechanical loading determines the durability of the nanocrystalline two-phase alloys such as superalloys, which are composite materials. The emergence of excess non-equilibrium vacancies, the activation of diffusion processes and the pore growth occur under the influence of thermo-mechanical loading. However, kinetics of the emergence and evolution of the excess vacancy concentration at various kinds of thermo-mechanical loading arising during the operation process have not been investigated yet. In this paper, the vacancy concentration in the one-dimensional model for thermo-mechanical loading including cyclic tensile stresses, thermal stresses and heating to high temperature taking into account microstructure is calculated. The considerable supersaturation of non-equilibrium vacancies arises in nanostructured alloys under the influence of thermo-mechanical loading. The rising of diffusion may occur at a critical value of excess vacancies as part of the diffusion-deformation stability mechanism, when small local fluctuation of excess vacancy concentration begins to grow. The growth occurs due to a Gibbs energy decrease in the increased vacancy concentration caused by the influence of thermo-mechanical stresses.