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The Effect of Rapid Annealing on Microstructure and Mechanical Properties of Severely Deformed Copper

Nobakht, Saeed | 2016

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 48405 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Kazeminezhad, Mohsen
  7. Abstract:
  8. Commercial pure copper sheets after primary annealing were severely deformed to amount of 2.32 by Constrained Groove Pressing (CGP) method. These sheets were undergone to electrical current at different heating times of 0.5, 1, 2, and 3 seconds up to four maximum temperatures of 150, 200, 250, and 300 °C without holding time. In order to compare the annealing by electrical current and without electrical current, four other samples were heated to 300 °C with holding times of 60, 90, 120, and 150 seconds in salt bath. Then, samples microstructure evolutions, hardness and shear stress values were investigated. Generally, the results depicted that inducing electrical current can accelerate the recrystallization process due to decreasing of incubation time for nucleation. So, with heating to two maximum temperatures of 250 and 300 °C, even in a little time of 0.5, 1, 2, and 3 seconds, the recrystallization process was completed and equiaxed grains were formed. But in maximum temperatures of 150 and 200 °C in order to lower temperature than the mentioned temperatures, partial recrystallization was observed. In the annealed sample with electrical current, during primary stages of recrystallization, great numbers of grown nuclei were observed with homogeneous distribution. These numbers of grown nuclei and their homogenous distribution were not observed in samples annealed at salt bath. The results of hardness and shear punch tests depicted that in contrast to controversial annealing process in which the work softening promotes with increasing the heating time, in the electrical annealing process it does not occur. This issue returns to interaction between electrical current effect and heating effect on recrystallization. So, with increasing the time, the heating effect due to increasing the diffusion time is increased and the electrical current effect is reduced. Also, the results showed that the homogeneous normalized displacement in shear punch tests of the samples annealed with the electrical current in a short time can approach to homogeneous normalized displacement of annealed sample in furnace (in 750°C for 3hr). This promotion in ductility of annealed samples by electrical current is due to significant reduction in dislocation density and development of a compressive stress in adjacent to defects and more atomic diffusion in next to these defects
  9. Keywords:
  10. Copper ; Rapid Annealing ; Severe Plastic Deformation ; Electric Current

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