Piecewise model with two overlapped stages for the structure formation and hardening upon severe plastic deformation

The evolution of metals micro/nano-structure upon severe plastic deformation (SPD) is still far to be theoretically explained, while experimental datasets are persistently growing. Major problem associated with understanding of SPD is a synergetic effect of several competing processes which alter material structure. In this paper we propose a model to reveal, as free-fitting parameters, strain breakpoints where predominantly one mechanism determines the micro/nano-structure in SPD materials from material hardness vs true strain experimental data. The model is applied to analyse SPD data for pure polycrystalline iron and two distinctive strain breakpoints have been revealed.