Investigation of Energy Stored in Copper Processed by Combination of SPD Methods

A. Gimazov1, A. Zhilyaev2,3
1LLC «BashNIPIneft», 86/1 Lenina street, 450039, Ufa, Russia
2Fundació CTM Centre Tecnològic, Plaça de la Ciencia 2, Manresa, Barcelona, 08242, Spain
3Institute for metals superplasticity problems RAS, 39 Stepan Khalturin street, 450001, Ufa, Russia
Abstract
A calorimetric study of commercial pure copper processed by combination of severe plastic deformation methods - high-pressure torsion, equal channel angular pressing and machining was performed. Calculated activation energy and enthalpy for the three peaks observed in the curves of differential scanning calorimetry defined relaxation processes corresponding to these peaks: the first peak – redistribution dislocations without the formation of new grain boundaries, the second peak – redistribution dislocations with partial annihilation and formation of low-angle grain boundaries, the third peak – recrystallization. Comparative analysis showed that the differential scanning calorimetry curves for samples subjected to high-pressure torsion deformation and sequencing methods of equal-channel angular pressing and high-pressure torsion showed no presence of the second peak. For samples in which the processing method involved machining, second peak detected steadily and is characterized by high values of enthalpy. It is shown that the difference in the curves for the various combinations of methods of intensive plastic deformation associated with substantially different processing speed, which leads to increased twins concentration in deformed material that impede cross slip migration of dislocation, thereby contributing to their accumulation in the material and prevent redistribution on the early stages of heating. Increased concentration of dislocation is used in the process of forming a microstructure that provides a structure with a smaller average grain size, which leads to an increase in the microhardness of the high-speed deformed materials compared with the samples slowly deformed.
Received: 28 August 2016   Revised: 08 September 2016   Accepted: 08 September 2016
Views: 70   Downloads: 39
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