Energy stored during high pressure torsion of pure metals

In the paper a problem of estimating the energy released during plastic deformation of pure metals by the high-pressure torsion (HPT) method is discussed. The work accomplished during plastic deformation by torsion under high pressure implies considerable heating of the sample. However, measurements using thermocouples located near the deformation zone show a temperature rise in the range of 5-50 degrees. As an example, pure nickel was chosen, for which there are experimental data on the kinetics of the formation of vacancies and dislocations in the process of torsion under high pressure and data on the refinement of the microstructure in the HPT process. It has been established that the amount of heat expended in heating the massive anvils would be sufficient to evaporate the nickel disc. The energy of formation of crystal structure defects (vacancies, dislocations, and high-angle grain boundaries) in nickel subjected to high-pressure torsion is also estimated. The correct equation for calculating the magnitude of the equivalent strain at simple shear is presented. It is shown that this calculation leads to a good agreement between the values of plastic energy and the work expended on the formation of the defective structure and heating of the sample-anvil system. Using the von Mises equation for calculations leads to the value of the work done during plastic deformation by torsion, which is two orders of magnitude higher than the upper estimate of the energy spent on heating the anvil and the formation of defects (vacancies, dislocations and new grain boundaries) of the crystal lattice. An asymptotic equation is proposed for calculating the value of equivalent strains for small (<1) and large (>2) shear strain degrees.