Journal of the Korea Institute of Military Science and Technology (한국군사과학기술학회지)

The Korea Institute of Military Science and Technology (한국군사과학기술학회)
권호 표지
DOI QR코드

DOI QR Code

A Study on the Microstructure and Anisotropic Mechanical Properties of Oxygen-Free Copper Fabricated by Equal Channel Angular Pressing

ECAP공법으로 제조된 무산소동의 미세조직 및 기계적 성질 이방성에 대한 고찰

  • Lee, Jaekun (2nd Research Division, Research and Development Institute) ;
  • Hong, Younggon (Department of Materials Science and Engineering, Pohang University of Science and Technology) ;
  • Kim, Hyoungseop (Department of Materials Science and Engineering, Pohang University of Science and Technology) ;
  • Park, Sunghyuk (School of Materials Science and Engineering, Kyungpook National University)
  • 이재근 ((주)풍산기술연구원 연구2실) ;
  • 홍영곤 (포항공과대학교 신소재공학과) ;
  • 김형섭 (포항공과대학교 신소재공학과) ;
  • 박성혁 (경북대학교 신소재공학부)
  • Received : 2019.05.03
  • Accepted : 2019.07.05
  • Published : 2019.08.05
Download PDF
⟨ Previous Next ⟩

Abstract

Equal channel angular pressing(ECAP) is a severe plastic deformation technique capable of introducing large shear strain in bulk metal materials. However, if an ECAPed material has an inhomogeneous microstructure and anisotropic mechanical properties, this material is difficult to apply as structural components subjected to multi-axial stress during use. In this study, extruded oxygen-free copper(OFC) rods with a large diameter of 42 mm are extruded through ECAP by route Bc up to 12 passes. The variations in the microstructure, hardness, tensile properties, and microstructural and mechanical homogeneity of the ECAPed samples are systematically analyzed. High-strength OFC rods with a homogeneous and equiaxed-ultrafine grain structure are obtained by the repeated application of ECAP up to 8 and 12 passes. ECAPed samples with 4 and 8 passes exhibit much smaller differences in terms of the average grain sizes on the cross-sectional area and the tensile strengths along the axial and circumferential directions, as compared to the samples with 1 and 2 passes. Therefore, it is considered that the OFC materials, which are fabricated via the ECAP process with pass numbers of a multiple of 4, are suitable to be applied as high-strength structural parts used under multi-axial stress conditions.

Keywords

GSGGBW_2019_v22n4_492_f0001.png 이미지

Fig. 1. Schematic illustration of used ECAP die(a) and image showing specimens before and after ECAP process(b)

GSGGBW_2019_v22n4_492_f0002.png 이미지

Fig. 2. Shape and dimensions of tensile specimen

GSGGBW_2019_v22n4_492_f0003.png 이미지

Fig. 3. Inverse pole figure(IPF) maps at center region of samples with pass number of 0(a), 1(b), 2(c), 4(d), 8(e), and 12(f)

GSGGBW_2019_v22n4_492_f0004.png 이미지

Fig. 4. Misorientation angle distributions of initial and ECAPed samples(a), and variation in average misorientation angle with applied number of pass(b)

GSGGBW_2019_v22n4_492_f0005.png 이미지

Fig. 5. Variations in average grain size at top, center, and bottom regions and its standard deviation (SD) with number of pass

GSGGBW_2019_v22n4_492_f0006.png 이미지

Fig. 6. IPF maps at top(a), center(b), and bottom(c) regions of 12 pass-ECAPed sample

GSGGBW_2019_v22n4_492_f0007.png 이미지

Fig. 7. Distribution of rockwell hardness from top to bottom(a) and from left to right(b) of initial and ECAPed samples

GSGGBW_2019_v22n4_492_f0008.png 이미지

Fig. 8. Variation in average hardness and standard deviation of hardness with number of pass

GSGGBW_2019_v22n4_492_f0009.png 이미지

Fig. 9. True stress–strain curves of initial and ECAPed samples

GSGGBW_2019_v22n4_492_f0010.png 이미지

Fig. 10. Variations in average GOS and recrystallization fraction(a) and grain size, tensile strength, and hardness at center region (b) with number of pass

GSGGBW_2019_v22n4_492_f0011.png 이미지

Fig. 11. Image showing loading direction of axial and circumferential tensile specimens(a), and true stress-strain curves along axial and circumferential directions of samples with pass number of 0(b), 1(c), 2(d), 4(e), and 8(f)

GSGGBW_2019_v22n4_492_f0012.png 이미지

Fig. 12. Comparisons of tensile strength(a) and yield strength(b) along axial and circumferential directions

References

  1. R. Z. Valiev, “Nanostructuring of Metals by Severe Plastic Deformation for Advanced Properties,” Nat. Mater., Vol. 3, No. 8, pp. 511-516, 2004. https://doi.org/10.1038/nmat1180
  2. R. Z. Valiev, Y. Estrin, Z. Horita, T. G. Langdon, M. J. Zechetbauer, Y. T. Zhu, “Producing Bulk Ultrafine-Grained Materials by Severe Plastic Deformation,” JOM, Vol. 58, No. 4, pp. 33-39, 2006. https://doi.org/10.1007/s11837-006-0213-7
  3. R. Z. Valiev, R. K. Islamgaliev, I. V. Alexandrov, “Bulk Nanostructured Materials from Severe Plastic Deformation,” Prog. Mater. Sci., Vol. 45, No. 2, pp. 103-189, 2000. https://doi.org/10.1016/S0079-6425(99)00007-9
  4. R. Z. Valiev, I. V. Alexandrov, Y. T. Zhu, T. C. Lowe, “Paradox of Strength and Ductility in Metals Processed by Severe Plastic Deformation,” J. Mater. Res., Vol. 17, No. 1, pp. 5-8, 2002. https://doi.org/10.1557/JMR.2002.0002
  5. K. H. Song, H. S. Kim, W. Y. Kim, "Enhancement of Mechanical Properties and Grain Refinement in ECAP 6/4 Brass," Rev. Adv. Mater. Sci., Vol. 28, pp. 158-161, 2011.
  6. E. A. El-Danaf, M. S. Soliman, A. A. Almajid, M. M. El-Rayes, “Enhancement of Mechanical Properties and Grain Size Refinement of Commercial Purity Aluminum 1050 Processed by ECAP,” Mater. Sci. Eng., A, Vol. 458, No. 1, pp. 226-234, 2007. https://doi.org/10.1016/j.msea.2006.12.077
  7. A. P. Zhilyaev, T. G. Langdon, “Using High-Pressure Torsion for Metal Processing: Fundamentals and Applications,” Prog. Mater. Sci., Vol. 53, No. 6, pp. 893-979, 2008. https://doi.org/10.1016/j.pmatsci.2008.03.002
  8. R. Kapoor, A. Sarkar, R. Yogi, S. K. Shekhawat, I. Samajdar, J. K. Chakravartty, "Softening of Al During Multi-Axial Forging in a Channel Die," Mater. Sci. Eng., A, Vol. 560, pp. 404-412, 2013. https://doi.org/10.1016/j.msea.2012.09.085
  9. M. Shaarbaf, M. R. Toroghinejad, “Nano-Grained Copper Strip Produced by Accumulative Roll Bonding Process,” Mater. Sci. Eng., A, Vol. 473, No. 1-2, pp. 28-33, 2008. https://doi.org/10.1016/j.msea.2007.03.065
  10. W. J. Kim, K. E. Lee, S. H. Choi, “Mechanical Properties and Microstructure of Ultra Fine-Grained Copper Prepared by a High-Speed-Ratio Differential Speed Rolling,” Mater. Sci. Eng., A, Vol. 506, No. 1-2, pp. 71-79, 2009. https://doi.org/10.1016/j.msea.2008.11.029
  11. R. Z. Valiev, T. G. Langdon, “Principles of Equal-Channel Angular Pressing as a Processing Tool for Grain Refinement,” Prog. Mater. Sci., Vol. 51, No. 7, pp. 881-981, 2006. https://doi.org/10.1016/j.pmatsci.2006.02.003
  12. W. Kim, H. H. Lee, S. J. Seo, J. K. Lee, T. S. Yoon, H. S. Kim, “Evaluation of Homogeneous Ultra-Fine Grain Refinements via Equal Channel Angler Pressing Process,” Trans. Mater. Process., Vol. 27, No. 4, pp. 222-226, 2018. https://doi.org/10.5228/KSTP.2018.27.4.222
  13. M. Kato, "Hall-Petch Relationship and Dislocation Model for Deformation of Ultrafine-Grained and Nanocrystalline Metals," Mater. Trans., JIM, Vol. 55, No. 1, pp. 19-24, 2014. https://doi.org/10.2320/matertrans.MA201310
  14. M. E. Kassner, "Taylor Hardening in Five Power Law Creep of Metals and Class M Alloys," Acta Mater., Vol. 52, pp. 1-9, 2004. https://doi.org/10.1016/j.actamat.2003.08.019
  15. L. Lapeire, J. Sidor, P. Verleysen, K. Verbeken, I. De Graeve, H. Terryn, L. A. I. Kestens, "Texture Comparison between Room Temperature Rolled and Cryogenically Rolled Pure Copper," Acta Mater., Vol. 95, pp. 224-235, 2015. https://doi.org/10.1016/j.actamat.2015.05.035
  16. L. S. Toth, C. Gu, "Ultrafine-Grain Metals by Severe Plastic Deformation," Mater. Charact., Vol. 92, pp. 1-14, 2014. https://doi.org/10.1016/j.matchar.2014.02.003