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S. Ohsaki *, D. Raabe , K. Hono *

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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 conference, Boston

  2. Übersicht • Motivation andMethods • Results • Discussion • Outlook and open questions

  3. Motivation: High strengthresistiveconductors • High strengthelectricalconductors: Multiphase materials; here: Cu-5 at.% Ag-3 at.% Nb (Cu-8.2wt%Ag-4wt%Nb) in-situ composite • Co-deformationmechanismsat large strains (mechanicalalloying; phasedissolution; dislocations in confined geometries; hetereophasedislocationtransmission; amorphization; conductivity) • Melt, cast, wire; SEM, TEM, APT Raabe, Mattissen: Acta Mater 46 (1998) 5973

  4. Nb Ag/Cu Cu WhyCu-5 at.% Ag-3 at.% Nb ternary binary nm-spacing: highstrength lowscattering Raabe, Mattissen: Acta Mater. 47 (1999) 769

  5. Übersicht • Motivation andMethods • Results • Discussion • Outlook and open questions

  6. 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

  7. Binary vs. ternarystrategy Raabe, Mattissen: Acta Mater.47 (1999) 769

  8. 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

  9. 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

  10. Nbfiber: h=10.0 Nb phase Cu→40~60at% Nb→20~50at% Ag→5~28at%

  11. Ag fiber: h=10.0 Drawing direction

  12. h=10.0 Ag phase Dislocation density 4.0×1016m-2 Raabe, Ohsaki, Hono: Acta Mater. 57 (2009) 5254

  13. 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

  14. Übersicht • Motivation andMethods • Results • Discussion • Outlook and open questions

  15. 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

  16. Discussion: mechanically-induced mixing

  17. 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.

  18. Discussion: mechanically-induced mixing and amorphization

  19. Übersicht • Motivation andMethods • Results • Discussion • Outlook and open questions D. Raabe: Advanced Materials 14 (2002) p. 639

  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)

  21. D. Raabe, F. Heringhaus: phys. stat. sol. (a) 142 (1994) 473481 Correlation of superconductivity and microstructure in an in-situ formed Cu-20%Nb composite U. Hangen, D. Raabe: phys. stat. sol. (a) 147 (1995) 515527 Experimental investigation and simulation of the normal conducting properties of a heavily cold rolled Cu-20mass% Nb in situ composite D. Raabe, U. Hangen: Materials Letters 22 (1995) 155161 Observation of amorphous areas in a heavily cold rolled Cu-20wt.% Nb composite F. Heringhaus, D. Raabe, G. Gottstein: Acta Metall. 43 (1995) 14671476 On the correlation of microstructure and electromagnetic properties of heavily cold worked Cu-20 wt.% Nb wires D. Raabe, F. Heringhaus, U. Hangen, G. Gottstein: Z. Metallk. 86 (1995) 405422 Investigation of a Cu-20mass%Nb in situ Composite Part I: Fabrication, Microstructure and Mechanical Properties Part II: Electromagnetic Properties and Application U. Hangen, D. Raabe: Acta Metall 43 (1995) 40754082 Modelling of the yield strength of a heavily wire drawn Cu-20%Nb composite by use of a modified linear rule of mixtures D. Raabe, U. Hangen: Journal of Materials Research 12 (1995) 30503061 Investigation of structurally less ordered areas in the Nb filaments of a heavily cold rolled Cu-20wt.% Nb in-situ composite D. Raabe, U. Hangen: Acta metall. 44 (1996) 953961 Correlation of microstructure and type II superconductivity of a heavily cold rolled Cu-20mass% Nb in situ composite D. Raabe, U. Hangen: phys. stat. sol. (a) 154 (1996) 715726 On the anisotropy of the superconducting properties of a heavily cold rolled Cu-20 mass% Nb in situ composite D. Raabe, D. Mattissen: Acta Mater. 46 (1998) 59735984 Microstructure and mechanical properties of a cast and wire drawn ternary Cu-Ag-Nb in situ composite D. Raabe, D. Mattissen: Acta Mater. 47 (1999) 769777 Experimental investigation and Ginzburg–Landau modeling of the microstructure dependence of superconductivity in CuAgNb wires D. Mattissen, D. Raabe, F. Heringhaus: Acta Mater. 47 (1999) 16271634 Experimental investigation and modeling of the influence of microstructure on the resistive conductivity of a Cu–Ag–Nb in situ composite