Tkachenko V. Structure and mechanical properties of copper after twist extrusion, thermal and deformation influences

The thesis is devoted to the study of principles of formation of submicrocrystalline structure and mechanical properties of copper for the twist extrusion, to study the influence of thermal and deformation effects on the structure and mechanical properties of copper. Copper deformed by twist extrusion were investigated by optical microscope, transmission and scanning electron microscope, X-ray diffractin, measurement of microhardness and density methods. It is shown that a change in the structure of copper with increasing degree of deformation is due to simultaneous development of intragranular dislocation slip and dynamic recrystallization. The result is an increase in the dislocation density and the fragmentation of the grain structure at the initial stages of deformation, and an increase in the number of high-angle boundaries with maintaining average size of structural elements at a constant level in the later stages of deformation. It is established that the formation of high values of both strength and plastic properties of copper at the early stages of twist extrusion and maintaining of these values with further increase in the degree of deformation due to presence of small grains and dynamically recrystallized grains in the structure. It is established that under the action of applied stress in the course of rolling of copper deformed by twist extrusion the change of the defect structure of the material is on the intragranular dislocation slip resulting in further accumulation of dislocations, grain fragmentation and increase in the strength properties.