The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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Dynamic Strain Aging of Austenitic Stainless Steels and Ni-Base Alloys

Mykola Ivanchenko

Doctoral dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Faculty of Engineering and Architecture for public examination and debate in Auditorium K216 at the Aalto University School of Science and Technology (Espoo, Finland) on the 19th of November 2010 at 12 noon.

Overview in PDF format (ISBN 978-952-60-3445-4)   [1010 KB]
Dissertation is also available in print (ISBN 978-952-60-3444-7)

Abstract

Dynamic strain aging (DSA) affects mechanical properties of materials and promotes strain localization. DSA results in serrated plastic flow, which was observed by means of constant extension rate tensile (CERT) tests in different grades of AISI 316 austenitic stainless steel and Ni-base alloys Alloy 600 and Alloy 690 in the temperature range of 200 – 600 °C and values of strain rate from 10−6 to 10−3 s−1. Negative strain rate sensitivity was reported for the studied materials at temperatures and strain rates where serrated plastic flow appeared. The map for the occurrence of serrated flow as a function of strain rate and temperature was built for the materials. The activation enthalpies of dynamic strain aging appearance were found to be 120 kJ/mol for the austenitic stainless steel and 159 kJ/mol for both Ni-base alloys. The internal friction (IF) peak associated with the interstitial atoms of nitrogen and carbon in the solid solution of AISI 316NG austenitic stainless steel and Alloy 600 was reported. The activation enthalpies of nitrogen diffusion in AISI 316NG steel (140 kJ/mol) and carbon diffusion in Alloy 600 (162 kJ/mol), obtained by means of internal friction, correspond well to the activation enthalpies of DSA appearance. The height of the internal friction peak increases depending on the pre-straining conditions in the similar way for AISI 316NG steel and Alloy 600. Annealing in situ at the IF peak temperature results in the decay of the IF peak enhanced by pre-straining for both materials. At the initial stage, the peak annealing processes can be described as an exponential decay function with characteristic times of 0.95 and 0.92 ks for AISI 316NG steel and Alloy 600, respectively. Transmission electron microscopy was performed on the specimens of AISI 316NG steel after CERT tests at temperatures of 400 and 200 °C, where serrated and smooth plastic flow was observed, respectively. Long-range planarity was observed in the dislocation structures of the specimen tested at 400 °C. The microstructure of the specimen strained at 200 °C exhibited cellular dislocation structure. It was concluded, that the diffusive re-distribution of interstitial atoms in the DSA regime affected the deformation behavior of the material by restricting dislocation cross-slip, which in turn promotes strain localization, affecting the mechanical performance of the material.

This thesis consists of an overview and of the following 6 publications:

  1. Mykola Ivanchenko, Ulla Ehrnstén, Vitaliy Nevdacha, Yuriy Yagodzinskyy, and Hannu Hänninen. 2004. Dynamic strain aging of nitrogen-alloyed AISI 316L stainless steel. In: Nuri Akdut, Bruno C. De Cooman, and Jaques Foct (editors). Proceedings of the 7th International Conference on High Nitrogen Steels 2004. Ostend, Belgium. 19-22 September 2004. GRIPS' Sparkling World of Steel, volume 1: Proceedings, number 4, pages 641-649. ISBN 3-937057-09-9. © 2004 GRIPS media. By permission.
  2. U. Ehrnstén, M. Ivanchenko, V. Nevdacha, Y. Yagodzinskyy, A. Toivonen, and H. Hänninen. 2005. Dynamic strain ageing and EAC of deformed nitrogen-alloyed AISI 316 stainless steels. In: Todd R. Allen, Peter J. King, and Lawrence Nelson (editors). Proceedings of the 12th International Conference on Environmental Degradation of Materials in Nuclear Power Systems – Water Reactors. Salt Lake City, Utah, USA. 14-18 August 2005. TMS. Pages 1475-1482. ISBN 1-604-23633-7. © 2005 The Minerals, Metals & Materials Society (TMS). By permission.
  3. Wade Karlsen, Mykola Ivanchenko, Ulla Ehrnstén, Yuriy Yagodzinskyy, and Hannu Hänninen. 2009. Microstructural manifestation of dynamic strain aging in AISI 316 stainless steel. Journal of Nuclear Materials, volume 395, numbers 1-3, pages 156-161. © 2009 Elsevier Science. By permission.
  4. M. Ivanchenko, Y. Yagodzinskyy, and H. Hänninen. 2009. Effect of plastic deformation on anelastic mechanical losses in multicomponent substitutional austenitic alloys. Materials Science and Engineering A, volumes 521-522, pages 121-123. © 2009 Elsevier Science. By permission.
  5. H. Hänninen, M. Ivanchenko, Y. Yagodzinskyy, V. Nevdacha, U. Ehrnstén, and P. Aaltonen. 2005. Dynamic strain aging of Ni-base alloys Inconel 600 and 690. In: Todd R. Allen, Peter J. King, and Lawrence Nelson (editors). Proceedings of the 12th International Conference on Environmental Degradation of Materials in Nuclear Power Systems – Water Reactors. Salt Lake City, Utah, USA. 14-18 August 2005. TMS. Pages 1423-1430. ISBN 1-604-23633-7. © 2005 The Minerals, Metals & Materials Society (TMS). By permission.
  6. M. Ivanchenko, V. Nevdacha, Y. Yagodzinskyy, and H. Hänninen. 2006. Internal friction studies of carbon and its redistribution kinetics in Inconel 600 and 690 alloys under dynamic strain aging conditions. Materials Science and Engineering A, volume 442, numbers 1-2, pages 458-461. © 2006 Elsevier Science. By permission.

Keywords: dynamic strain aging, austenitic stainless steel, Ni-base alloy, mechanical spectroscopy, transmission electron microscopy

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Last update 2011-05-26