Segregation Stabilizes Nanocrystalline Bulk Steel with Near Theoretical Strength

Yujiao Li, Dierk Raabe, Michael Herbig, Pyuck-Pa Choi, Shoji Goto, Aleksander Kostka, Hiroshi Yarita, Christine Borchers, and Reiner Kirchheim
Phys. Rev. Lett. 113, 106104 – Published 5 September 2014
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Abstract

Grain refinement through severe plastic deformation enables synthesis of ultrahigh-strength nanostructured materials. Two challenges exist in that context: First, deformation-driven grain refinement is limited by dynamic dislocation recovery and crystal coarsening due to capillary driving forces; second, grain boundary sliding and hence softening occur when the grain size approaches several nanometers. Here, both challenges have been overcome by severe drawing of a pearlitic steel wire (pearlite: lamellar structure of alternating iron and iron carbide layers). First, at large strains the carbide phase dissolves via mechanical alloying, rendering the initially two-phase pearlite structure into a carbon-supersaturated iron phase. This carbon-rich iron phase evolves into a columnar nanoscaled subgrain structure which topologically prevents grain boundary sliding. Second, Gibbs segregation of the supersaturated carbon to the iron subgrain boundaries reduces their interface energy, hence reducing the driving force for dynamic recovery and crystal coarsening. Thus, a stable cross-sectional subgrain size <10nm is achieved. These two effects lead to a stable columnar nanosized grain structure that impedes dislocation motion and enables an extreme tensile strength of 7 GPa, making this alloy the strongest ductile bulk material known.

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  • Received 8 February 2014

DOI:https://doi.org/10.1103/PhysRevLett.113.106104

© 2014 American Physical Society

Authors & Affiliations

Yujiao Li1,2,*, Dierk Raabe1,†, Michael Herbig1, Pyuck-Pa Choi1, Shoji Goto1,3, Aleksander Kostka1, Hiroshi Yarita4, Christine Borchers2, and Reiner Kirchheim1,2

  • 1Max-Planck Institut für Eisenforschung, Max-Planck-Strasse 1, D-40237 Düsseldorf, Germany
  • 2Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, D-37077 Göttingen, Germany
  • 3Akita University, Tegata Gakuencho, Akita 010-8502, Japan
  • 4Suzuki Metal Industry Co. LTD., Narashino, Chiba 275-8577, Japan

  • *Corresponding author. y.li@mpie.de
  • Corresponding author. d.raabe@mpie.de

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Issue

Vol. 113, Iss. 10 — 5 September 2014

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