Physics of megaplastic (Severe) deformation in solids

Cyclic character of the evolution of the defect structure and the properties of metallic materials during megaplastic deformation

“…More over, in terms of this approach, nonequilibrium evolu tion thermodynamics, and the existence of additional elastic energy relaxation channels during MPD [1,5], it was convincingly showed that the MPD processes in metals and solid solutions at room temperature should be accompanied by dynamic recrystallization. This assumption has found numerous experimental evi dences (see, e.g., [6]).…”

“…To a first approximation, such a model can be applied to describe the phenomena related to the periodicity of deformation fragmenta tion and recrystallization of grains. In this case, the set of evolution equations for grain boundaries and dislo cations can be generalized in the form (1) Here, h i is the defect density (subscript i = g and D for grain boundaries and dislocations, respectively), t and t' is the time, ϕ i is the defect energy, γ i is the kinetic coefficient, f i (t') is the kernel of the integral transfor mation that describes the degree (rate) of "forgetting" of the previous states, and T i is the time interval within which the system fully forgets the previous states. In addition, h g and h D are the volume densities of the total grain boundary surface and the total length of disloca tion lines, respectively; ϕ g is the surface energy density of grain boundaries in a steady state; and ϕ D is the dis location energy per dislocation length in a steady state.…”

“…The formation of a defect structure in solids and the accompanying physical and mechanical properties usually proceed monotonically, when a limiting state is reached. How ever, there exist cases where this process is nonmono tonic, quasi periodic, when the structure and the properties of a material tend toward the limiting asymptotic values and execute periodic damped oscil lations [1].…”

Multidimensional thermodynamic potential for descriptions of ultrathin lubricant film melting between two atomically smooth surfaces

“…A new basic quantity, i.e., the non-equilibrium entropys, is introduced here describing the part of thermomotion, which is conditioned by non-equilibrium character of the thermal distribution. Exactly this part of the entropy is produced owing to dynamic transition processes at generation of the free volume during external action, tending to some stationary value [26][27][28][29][30][31]. The equilibrium entropy does not evolve in the ordinary understanding, but changes with time due to relaxation of non-equilibrium entropy and its transition into the equilibrium subsystem.…”

“…An output can be found using a multidimensional thermodynamic potential from which the set of Landau-like kinetic equations must follow by standard procedure of differentiation [25]. Earlier this approach was applied for description of the processes of severe plastic deformation (SPD) [26][27][28] and fracture of quasibrittle solids [29]. The latest advances and statistical justification of this approach are outlined in works [30][31][32].…”