Resolving the FCC/HCP interfaces of the γ' (Ag2Al) precipitate phase in aluminium

Zezhong Zhang, Julian M. Rosalie, Nikhil V. Medhekar, Laure Bourgeois

Research output: Contribution to journalArticleResearchpeer-review

3 Citations (Scopus)

Abstract

The γ' (Ag2Al) phase in the Al–Ag alloy system has served as a textbook example for understanding phase transformations, precipitating hexagonal close-packed (HCP) crystals in the face-centred cubic (FCC) aluminium matrix. The γ' precipitates display fully coherent interfaces at their broad facets and semicoherent interfaces at their edges. Shockley partial dislocations are expected to decorate the semicoherent interface due to the FCC-HCP structural transformation. Determining the exact locations and core structures of interfacial dislocations, however, remains challenging. In this study, we used aberration-corrected scanning transmission electron microscopy and atomistic simulations to re-visit this classical system. We characterised and explained the Ag segregation at coherent interfaces in the early stage of precipitation. For semicoherent interfaces, interfacial dislocations and reconstructions were revealed by bridging advanced microstructure characterisation and atomistic simulations. In particular, we discovered a new FCC/HCP interfacial structure that displays a unique combination of Shockley partial, Lomer-Cottrell and Hirth dislocations that evolve from the known interfacial structure purely composed by Shockley partial dislocations. Our findings show that the FCC-HCP transformation is more complex than hitherto considered, due to the interplay between structure and composition confined at interfaces.

Original languageEnglish
Pages (from-to)116-130
Number of pages15
JournalActa Materialia
Volume174
DOIs
Publication statusPublished - 1 Aug 2019

Keywords

  • Atomic structure
  • Atomistic simulation
  • Dislocation
  • Interface
  • Phase transformation
  • Scanning transmission electron microscopy (STEM)

Cite this

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abstract = "The γ' (Ag2Al) phase in the Al–Ag alloy system has served as a textbook example for understanding phase transformations, precipitating hexagonal close-packed (HCP) crystals in the face-centred cubic (FCC) aluminium matrix. The γ' precipitates display fully coherent interfaces at their broad facets and semicoherent interfaces at their edges. Shockley partial dislocations are expected to decorate the semicoherent interface due to the FCC-HCP structural transformation. Determining the exact locations and core structures of interfacial dislocations, however, remains challenging. In this study, we used aberration-corrected scanning transmission electron microscopy and atomistic simulations to re-visit this classical system. We characterised and explained the Ag segregation at coherent interfaces in the early stage of precipitation. For semicoherent interfaces, interfacial dislocations and reconstructions were revealed by bridging advanced microstructure characterisation and atomistic simulations. In particular, we discovered a new FCC/HCP interfacial structure that displays a unique combination of Shockley partial, Lomer-Cottrell and Hirth dislocations that evolve from the known interfacial structure purely composed by Shockley partial dislocations. Our findings show that the FCC-HCP transformation is more complex than hitherto considered, due to the interplay between structure and composition confined at interfaces.",
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Resolving the FCC/HCP interfaces of the γ' (Ag2Al) precipitate phase in aluminium. / Zhang, Zezhong; Rosalie, Julian M.; Medhekar, Nikhil V.; Bourgeois, Laure.

In: Acta Materialia, Vol. 174, 01.08.2019, p. 116-130.

Research output: Contribution to journalArticleResearchpeer-review

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