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2009 MRS Cu Based Composites

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  • 1. Mechanical alloying and amorphization in Cu-Nb-Ag in situ composite wires studied by TEM and atom probe tomography
    S. Ohsaki*, D. Raabe, K. Hono*
    * National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047, Japan
    Dierk Raabe 1. Dec. 2009, MRS Fall, Boston
  • 2. Übersicht
    • Motivation andMethods
    • 3. Results
    • 4. Discussion
    • 5. Outlook and open questions
  • Motivation: High strengthresistiveconductors
    • High strengthelectricalconductors: Multiphase materials; here: Cu-5 at.% Ag-3 at.% Nb (Cu-8.2wt%Ag-4wt%Nb) in-situ composite
    • 6. Co-deformationmechanismsat large strains (mechanicalalloying; phasedissolution; dislocations in confined geometries; hetereophasedislocationtransmission; amorphization; conductivity)
    • 7. Melt, cast, wire; SEM, TEM, APT
    Raabe, Mattissen: Acta Mater 46 (1998) 5973
  • 8. 3
    Nb
    Ag/Cu
    Cu
    WhyCu-5 at.% Ag-3 at.% Nb
    ternary
    binary
    nm-spacing:
    highstrength
    lowscattering
    Raabe, Mattissen: Acta Mater. 47 (1999) 769
  • 9. Übersicht
    • Motivation andMethods
    • 10. Results
    • 11. Discussion
    • 12. Outlook and open questions
    D. Raabe: Advanced Materials 14 (2002) p. 639
  • 13. 5
    Fibres; Cu-5 at.% Ag-3 at.% Nb (Cu-8.2 wt% Ag-4 wt% Nb)
    h=7.5
    h=8.6
    h=10.0
    Raabe, Ohsaki, Hono: Acta Mater. 57 (2009) 5254
  • 14. 6
    Binary vs. ternarystrategy
    Raabe, Mattissen: Acta Mater.47 (1999) 769
  • 15. 7
    298 K, influence of the size effect
    Experiment
    Model
    true strain
    Res. conduct.; Cu-5 at.% Ag-3 at.% Nb (Cu-8.2 wt% Ag-4 wt% Nb)
    relative change in resistivity
  • 16. 8
    Nano-beam energy dispersive x-ray spectroscopy (EDS)
    Point 1: Cu matrix
    Point 2: Nb filament
    Points 3-6: Nb and Ag with varying fractions, partly because of the convolution effect of EDS
    Point 7: Ag fiber.
    Dominance of Cu
    Points 1 and 2: minor Nb contribution
    Points 3-6: considerable Ag contribution
    Strong co-existence of Cu and Ag within the same beam probes
    Raabe, Ohsaki, Hono: Acta Mater. 57 (2009) 5254
  • 17. Nbfiber: h=10.0
    Nb phase
    Cu->40~60at%
    Nb->20~50at%
    Ag->5~28at%
  • 18. Ag fiber: h=10.0
    Drawing direction
  • 19. h=10.0 Ag phase
    Dislocation density 4.0×1016m-2
    Raabe, Ohsaki, Hono: Acta Mater. 57 (2009) 5254
  • 20. h=10.0 Nb phase
    Amorphization at Cu/Nb interface
    D. Raabe, U. Hangen: Materials Letters 22 (1995) 155161; D. Raabe, F. Heringhaus, U. Hangen, G. Gottstein: Zeitschrift für Metallkunde 86 (1995) 405422; D. Raabe, U. Hangen: Journal of Materials Research 12 (1995) 30503061
    see also: X.Sauvage: University of Rouen
  • 21. Übersicht
    • Motivation andMethods
    • 22. Results
    • 23. Discussion
    • 24. Outlook and open questions
  • 14
    Discussion: mechanically-induced mixing
    Classical difffusion
    Cu-Nb and Cu-Ag: negligible solubility
    No thermodynamic driving force for mixing
    Interface thermodynamics and solubility
    No negative enthalpy of mixing in case of crystalline phase
    Also Gibbs–Thomson effect and internal stresses do not provide negative mixing enthalpy
    Annealing: immediate de-mixing and spherodization
    Plasticity-assisted diffusion
    Deformation-induced increase in vacancy density
    All phases in the alloy, i.e. Cu, Ag, and Nb plastically strained
    An increased vacancy concentration should be present in all phases
    If higher defect densities enhance diffusion, the mixing profiles should be symmetric
    Atomic-scale interface roughening
    Pipe diffusion
    Segregation and diffusion to dislocation cores in neighbor phase
    Dislocation shuffle
    Raabe, Ohsaki, Hono: Acta Mater. 57 (2009) 5254
  • 25. 15
    Discussion: mechanically-induced mixing
  • 26. 16
    Discussion: mechanically-induced amorphization
    Pure Cu, Ag, and Nb wires not amorphous during wire drawing
    Relationship between mechanical alloying, enthalpy of mixing of the newly formed compounds, and subsequent amorphization.
    Abutting phase of an amorphous Cu region shows high dislocation densities
    Cu matrix becomes amorphous only when mechanically alloyed.
    Occurs in Cu-Nb, Cu-Nb-Ag, and Cu-Zr: In all cases at least one pair of the constituent elements reveal a negative enthalpy of mixing.
    Gibbs free energy - concentration diagram reveals amorphous Cu-Nb phase between 35 at.% and 80 at.% relative to the BCC and FCC solid solutions that could be formed by forced mixing. Our measurements fall in this regime. The atomic radius mismatch is 12.1% for Cu-Nb, 13.1% for Cu-Ag, and even 24.4% for Cu-Zr.
    Total free energy change due to dislocation energy not enough
    Amorphization in a two step mechanism:
    Dislocation-shuffling /trans-phase plastic deformation and mixing
    Amorphization in regions with both, heavy mixing and high dislocation densities
    Likely in systems which fulfill at least some of the classical glass forming rules.
  • 27. 17
    Discussion: mechanically-induced mixing and amorphization
  • 28. 18
  • 29. Übersicht
    • Motivation andMethods
    • 30. Results
    • 31. Discussion
    • 32. Outlook and open questions
    D. Raabe: Advanced Materials 14 (2002) p. 639
  • 33. 20
    Outlook and open questions
    Mechanism of mechanical alloying and amorphization
    Superconductivity and proximity effects dependent on local mechanical mixing
    Cu-5 at.% Ag-3 at.% Nb
    (Cu-8.2wt%Ag-4wt%Nb)