The impact of high hydrostatic pressure maintenance after high-pressure torsion on phenomena during high hydrostatic pressure annealing

Abstract

The impact of high hydrostatic pressure release after high-pressure torsion on subsequent high hydrostatic pressure annealing was analyzed by performing experiments on nanostructured Ni. Ni was deformed by high-pressure torsion at a pressure of 6 GPa in 5 turns. Directly after deformation, the pressure was reduced to 2 GPa, and under 2 GPa annealing at 400 °C was conducted for 5 min. For comparison, samples were also annealed under 2 GPa after deformation without loading between processes. Microhardness measurements, detailed microscopy observations and positron annihilation spectroscopy investigations were performed to elucidate the changes in the microstructures obtained after different processing routes. It is demonstrated that the pressure applied between deformation and high hydrostatic pressure annealing caused an increase in microhardness by 20% in comparison with pressure realize. Moreover, the pressure applied had an impact on the vacancy concentration, and consequently on the microstructure, leading to a smaller average grain size and a more heterogenous microstructure in terms of grain size, leaving space for optimizing the strength-ductility balance.