Thermodynamics of Fragmentation of Solids at Severe Plastic Deformation

Abstract

Using the Landau theory of phase transitions the fragmentation of solids during the process of severe plastic deformation (SPD) is studied. In describing of appearing defect structures the density of grain boundaries, dislocations and entropy are introduced. This allows us to take into account the two channels of energy dissipation (thermal one and defects formation). In the deterministic case phase diagram is determined establishing the domains of realization of different types of structures. The interaction effect of several types of defects is investigated on the formation of limiting structure in terms of internal energy. As shown, the grains size in limiting structures decreases with an increase of the elastic strain. Within the scope of the adiabatic approximation, at which change of the dislocations density follows the evolution of the density of the grain boundaries, the conditions of formation for two limiting structures are found. They correspond to the mode, in which there is a mixture of grains of different sizes.