2009 M R S Cu Based Composites
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1) The document examines mechanical alloying and amorphization in Cu-Nb-Ag in situ composite wires studied using TEM and atom probe tomography. 2) Results show the wires contain a nanoscale mixture of Cu, Nb, and Ag phases after drawing, with some regions becoming amorphized. 3) The mixing and amorphization are believed to occur through plastic deformation mechanisms like dislocation shuffling between phases, which increase vacancy concentrations and enable diffusion even where thermodynamics do not normally allow solubility. Regions of high dislocation density and mixing are most prone to amorphization.
2009 M R S Cu Based Composites
- 1. Mechanical alloying and amorphization in Cu-Nb-Ag in situ composite wires studied by TEM and atom probe tomographyS. Ohsaki*, D. Raabe, K. Hono** National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047, Japan1. Dec. 2009, MRS Fall, Boston
- 3. Results
- 4. Discussion
- 5. Outlook and open questionsMotivation: High strengthresistiveconductorsHigh 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, APTRaabe, Mattissen: Acta Mater 46 (1998) 5973
- 8. 3NbAg/CuCuWhyCu-5 at.% Ag-3 at.% Nbternarybinarynm-spacing:highstrengthlowscatteringRaabe, Mattissen: Acta Mater. 47 (1999) 769
- 10. Results
- 11. Discussion
- 12. Outlook and open questionsD. Raabe: Advanced Materials 14 (2002) p. 639
- 13. 5Fibres; Cu-5 at.% Ag-3 at.% Nb (Cu-8.2 wt% Ag-4 wt% Nb)h=7.5h=8.6h=10.0Raabe, Ohsaki, Hono: Acta Mater. 57 (2009) 5254
- 14. 6Binary vs. ternarystrategyRaabe, Mattissen: Acta Mater.47 (1999) 769
- 15. 7298 K, influence of the size effectExperimentModel true strainRes. conduct.; Cu-5 at.% Ag-3 at.% Nb (Cu-8.2 wt% Ag-4 wt% Nb)relative change in resistivity
- 16. 8Nano-beam energy dispersive x-ray spectroscopy (EDS) Point 1: Cu matrixPoint 2: Nb filamentPoints 3-6: Nb and Ag with varying fractions, partly because of the convolution effect of EDS Point 7: Ag fiber. Dominance of CuPoints 1 and 2: minor Nb contributionPoints 3-6: considerable Ag contributionStrong co-existence of Cu and Ag within the same beam probesRaabe, Ohsaki, Hono: Acta Mater. 57 (2009) 5254
- 18. Ag fiber: h=10.0Drawing direction
- 19. h=10.0 Ag phaseDislocation density 4.0×1016m-2 Raabe, Ohsaki, Hono: Acta Mater. 57 (2009) 5254
- 20. h=10.0 Nb phase Amorphization at Cu/Nb interfaceD. Raabe, U. Hangen: Materials Letters 22 (1995) 155161; D. Raabe, F. Heringhaus, U. Hangen, G. Gottstein: Zeitschrift für Metallkunde 86 (1995) 405422; D. Raabe, U. Hangen: Journal of Materials Research 12 (1995) 30503061see also: X.Sauvage: University of Rouen
- 22. Results
- 23. Discussion
- 24. Outlook and open questions14Discussion: mechanically-induced mixingClassical difffusionCu-Nb and Cu-Ag: negligible solubilityNo thermodynamic driving force for mixingInterface thermodynamics and solubilityNo negative enthalpy of mixing in case of crystalline phase Also Gibbs–Thomson effect and internal stresses do not provide negative mixing enthalpyAnnealing: immediate de-mixing and spherodizationPlasticity-assisted diffusionDeformation-induced increase in vacancy density All phases in the alloy, i.e. Cu, Ag, and Nb plastically strainedAn increased vacancy concentration should be present in all phasesIf higher defect densities enhance diffusion, the mixing profiles should be symmetricAtomic-scale interface rougheningPipe diffusionSegregation and diffusion to dislocation cores in neighbor phaseDislocation shuffle Raabe, Ohsaki, Hono: Acta Mater. 57 (2009) 5254
- 26. 16Discussion: mechanically-induced amorphizationPure Cu, Ag, and Nb wires not amorphous during wire drawingRelationship between mechanical alloying, enthalpy of mixing of the newly formed compounds, and subsequent amorphization. Abutting phase of an amorphous Cu region shows high dislocation densitiesCu 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 enoughAmorphization 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. 17Discussion: mechanically-induced mixing and amorphization
- 28. 18
- 30. Results
- 31. Discussion
- 32. Outlook and open questionsD. Raabe: Advanced Materials 14 (2002) p. 639
- 33. 20Outlook and open questionsMechanism of mechanical alloying and amorphizationSuperconductivity and proximity effects dependent on local mechanical mixingCu-5 at.% Ag-3 at.% Nb(Cu-8.2wt%Ag-4wt%Nb)