Slip systems and dislocation densities in individual grains of polycrystalline aggregates of plastically deformed CoTi and CoZr alloys

Tamás Ungár, Gábor Ribárik, Gyula Zilahi, Rupalee Mulay, Ulrich Lienert, Levente Balogh, Sean Agnew

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

A novel X-ray diffraction-based technique for grain-by-grain assessment of dislocation density within polycrystals is applied. The technique discriminates dislocation densities of different slip modes, slip systems and dislocation character. Data which was formerly confined to the transmission electron microscope (TEM) is now available from X-ray diffraction (XRD). In addition, there is a profound statistical advantage of the XRD approach over the traditional TEM-based approach. Over 130 grains were analyzed for one sample of CoTi, which would be a Herculean task on the TEM, requiring dozens of samples as well as numerous hours on the microscope and analysis of the images generated for each sample. The present experiments were performed in about 30 h per sample and the analysis is semi-automated, involving a Monte-Carlo-type algorithm to determine the dislocation structure best representing the single crystal diffraction peak profiles in a polycrystalline aggregate. Conclusive confirmation of a previously suggested explanation for the anomalous ductility of two CsCl structured intermetallic compounds, CoTi and CoZr, is provided: namely, that c, with b =(1 1 0) and(1 1 1), rarely observed in single crystal experiments, are active in nearly every grain. The results call into question the value of employing single crystal deformation experiments alone to understand the deformation behavior of polycrystalline materials. Further, the results re-emphasize that the uniform stress assumption implicit in Schmid factor analysis is a poor one for materials which are highly anisotropic at the single crystal level.

Original languageEnglish
Pages (from-to)264-282
Number of pages19
JournalActa Materialia
Volume71
DOIs
Publication statusPublished - Jun 2014

Keywords

  • B2 intermetallics plasticity
  • CoTi
  • CoZr
  • Dislocation densities
  • Slip systems

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Polymers and Plastics
  • Metals and Alloys

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