Formation and Stability of Ultrafine Structure of Commercial Purity Copper Deformed at 80 K

L. Voronova, M. Degtyarev, T. Chashchukhina, T. Gapontseva, V. Pilyugin show affiliations and emails
Received: 30 July 2018; Revised: 03 September 2018; Accepted: 20 September 2018
Citation: L. Voronova, M. Degtyarev, T. Chashchukhina, T. Gapontseva, V. Pilyugin. Formation and Stability of Ultrafine Structure of Commercial Purity Copper Deformed at 80 K. Lett. Mater., 2018, 8(4) 424-428
BibTex   https://doi.org/10.22226/2410-3535-2018-4-424-428

Abstract

The stages of the evolution of the structure of copper of commercial purity (99.9 wt% Cu) under cryogenic deformation by shear under pressure were studied. Mechanical twinning prevents the formation of a misoriented disperse structure and the development of recrystallization upon  heating up to room temperature.Evolution of the structure and microhardness of commercial copper have been studied after cryogenic (80 K) high pressure torsion performed at an angle of the anvil rotation from 15° to 10 revolutions. Slowing down of the dynamic softening processes due to impurity dragging allow us to establish stages of the structure change in commercial copper upon deformation, as compared to high-purity copper, in which recrystallization rapidly develops upon heating to room temperature significantly distorts a deformed structure and decreases the microhardness of the deformed copper. Two stages of deformation have been observed. Stages change at true strain e=7.3. Dislocation slip and mechanical twinning are the main structure-forming mechanisms at the first stage. No mechanical twins were found at the second stage. The second stage is characterized by misoriented microcrystallites which play the role of recrystallization centers upon heating up to room temperature. The average microcrystallite size is 0.1–0.2 μm. Microcrystallites provide low thermal stability of the structure. Some grains in the structure formed at the second stage of deformation can grow up to several microns for 1–2 days; the fraction of the recrystallized structure is 20%. Holding for 3 years almost completes the recrystallization; the maximum size of recrystallized grains is 100 μm. Recrystallization at room temperature develops slowly in the structure with deformation twins: early signs of recrystallization are observed after 1.5 years after the end of the deformation; and the fraction of the recrystallized structure does not exceed 10%.

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