Thermostatistical theory of plastic deformation in metals

This work aims to describe plastic deformation and microstructure evolution of metals at various scales in terms of dislocation behaviour. The theory is based on statistical thermodynamics, where the entropy is proposed to incorporate the possible paths for dislocation motion. Other than estimating the velocity gradients a dislocation may reach, the number of possible paths (configurations) that are favourable in terms of free energy at a given temperature and strain rate are considered in the entropy. It is demonstrated that the entropy features strongly in plasticity: 1) Its description supplies a physical foundation to the Kocks–Mecking formulation across the scales at a variety of deformation conditions for FCC, BCC and HCP metals, by identifying the activation energy for dislocation annihilation. 2) The transitions from low, medium and high temperature dislocation annihilation mechanisms are physically explained. 3) It aids in describing the conditions for the formation of dislocation cells and their average size, as well as the work hardening behaviour at large strains in FCC and BCC metals. 4) Deformation twinning in HCP, FCC and nano–twinned copper can be described. 5) The transition tempera- tures where different twin modes predominate in HCP metals are predicted. 6) The dynamic recrystallisation behaviour in pure and multicomponent FCC systems can be described; the critical conditions for recrystallisation occurrence are obtained in terms of alloy’s composition and deformation parameters. 7) Solid solution effects in work hardening can be identified. All these results allow to describe various plasticity phenomena in terms of a single parameter: the average dislocation density.