Effect of deformation rate on microstructure and mechanical properties of metals subjected to large cold plastic deformation under high pressures

The aim of this project is to study the influence of deformation rate on the microstructure and mechanical properties of metals subjected to high cold plastic deformation under high pressures. In the era of constantly increasing industrial competition, production processes are being intensified (it is necessary to increase the production rate) and, at the same time, more and more stringent requirements are being set, leading to the creation of new materials with strictly defined mechanical properties. Intensification of plastic forming processes as well as the search for new, unconventional methods of volumetric forming necessitate the use of very high strain rates and conducting plastic deformation in a dynamic manner. To fully control the plastic deformation process under dynamic loading, it is necessary to analyze the effect of strain rate on the mechanics of plastic flow (plasticizing stress, strain inhomogeneity, etc.). It is generally known that the stress of a material increases with increasing strain rate, and this tendency is an inherent characteristic of the workpiece material. Hence, the behavior of materials during dynamic loading is variable depending on the material under study and in particular on its crystallographic structure.
The authors of this project use unconventional volumetric shaping methods, which are large plastic deformation SPD processes, such as hydrostatic HE extrusion and squeezing through an equiaxial angular channel ECAP as tools to investigate the influence of deformation rates on mechanical and microstructural properties of selected metals. Commonly described in the literature, such tests are performed in standard tensile or compression tests of materials in the initial or deformed state in a wide range of deformation rates. The effects of rate of plastic deformation on strengthening are then determined from the characteristics recorded during these processes and the microstructural properties are studied after the deformation process has taken place, e.g. by analysis of sample fractures or material texture. In particular, the results of these studies are negatively affected by adiabatic heating effects during dynamic testing at high strain rates. In the present study, the plastic deformation rate is realized in real high plastic deformation ECAP and HE processes and the strengthening tests are conducted by static tensile testing at standard rates on previously deformed materials with strongly limited adiabatic heating (intensive product cooling in both ECAP and HE processes).
The proposed research is novel and allows to obtain more reliable data on the influence of deformation rate on the microstructure of selected metals, i.e. its morphology, degree of deformation, grain size distribution during actual large plastic deformation processes and the resulting final mechanical properties. In the current project, the effect of deformation rate on the microstructure and mechanical properties of metals with three crystallographic structures, FCC (copper – Cu), BCC (iron – Fe α) and HCP (zinc – Zn) will be investigated in order to capture the differences in their sensitivity to plastic deformation rate and to verify the mechanisms responsible for these differences.