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Grain Boundary Mediated Displacive–Diffusional Formation of τ-Phase MnAl

  • Symposium: Structural Transitions and Local Deformation Processes at and near Grain Boundaries
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Abstract

Dynamic in situ heating and postmortem transmission electron microscopy studies, including high-resolution electron microscopy, have been performed for a near equiatomic composition of a Mn-Al-base permanent magnet alloy to investigate the mechanisms of the transformation of hexagonal close-packed ε-phase to a chemically ordered tetragonal τ-phase with a face-centered cubic-related L10 structure. Although a “massive” mode dominates the kinetics of this composition invariant transformation, we also observed the genesis of a morphologically plate-like τ-phase by partial dislocation glide, described as Shockley-type partials with respect to the L10 structure, and a transformation mode exhibiting displacive characteristics. The sources for the transformation dislocations facilitating the formation of the morphologically plate-like τ-phase were associated with the interfaces between the parent ε- and product τ-phase produced by the “massive” transformation mode. Our experiments revealed diffusional and displacive features of the mechanism accomplishing the formation of τ-MnAl with plate-like morphology. Hence, a hybrid displacive–diffusional mechanism has been identified, and the synergistic role of the nucleation interfaces of the massively transformed τ-phase has been discussed.

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Acknowledgments

The material presented in this article is based on work supported by the National Science Foundation. Any opinions, findings, conclusions, or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. We are grateful for the assistance of E.A. Stach and V. Radmilovic during in-situ heating TEM experiments, which have been performed with the JEM3010 at the National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, CA, and to H. Heinrich, now at the University of Central Florida, for assistance with HREM experiments performed with the 300 kV FEGTEM at the Eidgenössiche Technische Hochschule Zürich, Zürich, CH. Finally, we acknowledge the use of facilities of the Materials Micro-Characterization Laboratory in the Department of Mechanical Engineering and Materials Science of the University of Pittsburgh.

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Authors and Affiliations

  1. Swanson School of Engineering, Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA, 15261, USA

    Jorg M. K. Wiezorek (Professor) & Andreas K. Kulovits (Post Doctorate)

  2. Alcoa Technology Center, Alcoa Center, Pittsburgh, PA, 15212, USA

    Cagatay Yanar (Senior Development Scientist)

  3. Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA, 22904, USA

    William A. Soffa (Professor)

Authors
  1. Jorg M. K. Wiezorek
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  2. Andreas K. Kulovits
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  3. Cagatay Yanar
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  4. William A. Soffa
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Corresponding author

Correspondence to Andreas K. Kulovits.

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Manuscript submitted December 21, 2009.

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Wiezorek, J.M.K., Kulovits, A.K., Yanar, C. et al. Grain Boundary Mediated Displacive–Diffusional Formation of τ-Phase MnAl. Metall Mater Trans A 42, 594–604 (2011). https://doi.org/10.1007/s11661-010-0308-1

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  • DOI: https://doi.org/10.1007/s11661-010-0308-1

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