Stochastic Model of Structural States of Copper Under High Pressure Torsion in Bridgman Anvils

Despite the continuously expanding volume of experimental data on ultrafine-grained materials produced by severe plastic deformation, the occurrence of competing structure-forming processes (strengthening/relaxation) still requires a theoretical explanation. Based on the analysis of hardness data for technically pure copper subjected to shear under pressure in Bridgman anvils, the staging of strengthening was established. To account for the stochastic nature of the manifestation of relaxation processes during deformation, a model for analyzing material hardness data has been proposed, which is based on three postulates: (a) the structural response to hardness measurement, characteristic of its micro/nanostructural state, including the possible occurrence of a relaxation process, is considered as a random factor; (b) each structural state can be associated with its unique set of responses to hardness measurement; (c) the superposition of structural states is possible. It was shown that each structural response to hardness measurement can be associated with a specific structural state. Meanwhile, the evolution of hardness with applied deformation is a sequential change of combinations of three structural states (cell structure, microcrystalline without significant influence of dynamic recrystallization, and one formed by dynamic recrystallization), which determine the stages of strain hardening.