Microstructure and mechanical properties of ultrafine-grained fcc/hcp cobalt processed by a bottom-up approach

F. Fellah, G. Dirras, J. Gubicza, F. Schoenstein, N. Jouini, S. M. Cherif, C. Gatel, J. Douin

Research output: Contribution to journalArticle

18 Citations (Scopus)


Bulk Co samples having a mean grain size of ∼300 nm were processed by hot isostatic pressing of a high purity Co nanopowder synthesized by chimie douce. The grain interior exhibited a highly faulted nanoscale lamellar microstructure comprising an intricate mixture of face-centered cubic, hexagonal close-packed phases and nanotwins. Room temperature compression tests carried out at a strain rate of ∼2 × 10-4 s-1 revealed a yield stress of ∼1 GPa, a strain to rupture of ∼5%. During straining it was found that the hexagonal close-packed phase content increased from 55% to 65% suggesting a deformation mechanism based on stress-assisted face-centered cubic to hexagonal close-packed phase transformation. In addition, an apparent activation volume of ∼3b3 was computed which indicates that the deformation mechanism was controlled by dislocation nucleation from the numerous boundaries. Nonetheless, in such an intricate microstructure, the overall mechanical properties are discussed in term of a complex interplay between lattice dislocation plasticity, transformation-induced plasticity and possibly twin-induced plasticity.

Original languageEnglish
Pages (from-to)424-428
Number of pages5
JournalJournal of Alloys and Compounds
Issue number2
Publication statusPublished - Jan 21 2010


  • Mechanical properties
  • Microstructure
  • Powder metallurgy
  • Sol-gel processes
  • Transmission electron microscopy (TEM)
  • X-ray diffraction

ASJC Scopus subject areas

  • Mechanics of Materials
  • Mechanical Engineering
  • Metals and Alloys
  • Materials Chemistry

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