Conference lecture at ISMANAM Conference in Zurich 2010

1. Atomic-scale mechanisms in mechanical alloying Towards the limits of strength in ductile nano-structured bulk materials D. Raabe, Y.J. Li, P. Choi, X. Sauvage*, R. Kirchheim**, K. Hono*** Düsseldorf, Germany WWW.MPIE.DE d.raabe@mpie.de * Physique des Matériaux, University Rouen, France ** Max-Planck-Institut andPhysicsDpt. University Göttingen, Germany *** NIMS, Japan Thanksto: R. Pippan, J. D. Embury ISMANAM Conference 8, July2010 ETH Zürich

4. Example # 1– keymechanisms: Maraging - TRIP 1.5 GPa-steels: Maraging-TRIP steels: Fe 12-15 % MnNi Al Ti Weightreduction ( - 300 kg ) 3 Raabe et al. Adv. Eng. Mater. 11 (2009) 547

5. Example # 2– keymechanisms: Martensiterelaxationandaging 2 GPa-steels: Agedmartensite: Fe 13 Cr > 0.3 C Ultra highstrengthandcorrosionresistance 1.5 K/s (slab)  4000 K/s (strip) 4 steel research int. 79 (2008) No. 6

6. Example # 2– keymechanisms: Martensiterelaxationandaging 2 GPa-steels: Agedmartensite: Fe 13 Cr > 0.3 C carbon γ α‘ carbide 5 steel research int. 79 (2008) No. 6

7. Example # 3– keymechanisms: Nanostructures > 5 GPa-steels: Pearlite: nanostructuredandmechanicallyalloyed Data from Lesuer, Syn, Sherby and Kim, Metallurgy, Processing and Applications of metal wires, TMS, 1993; M.H. Hong, W.T. Reynolds, Jr., T. Tarui, K. Hono, Metall. Mater. Trans. A 30, 717 (1999); T. Tarui, N. Maruyama, J. Takahashi, S. Nishida, H. Tashiro, Nippon Steel Technical Report 91, 56 (2005); S. Goto, R. Kirchheim, T. Al-Kassab, C. Borchers, Trans. Nonferrous Met. Soc. China 17, 1129 (2007); J. Takahashi, T. Tarui, K. Kawakami, Ultramicroscopy 109, 193 (2009); A. Taniyama, T. Takayama , M. Arai, T. Hamada, Scripta Mater. 51, 53 (2004); [6] K. Hono, M. Ohnuma, M. Murayama, S. Nishida, A. Yoshie, Scripta Mater. 44, 977 (2001). 6

8. Example # 4– keymechanisms: Nanostructures > 2 GPa- Cu-alloys: Cu-Nb, Cu-Nb-Ag : nanostructuredandmechanicallyalloyed taken from K. Spencer, F. Lecouturier, L. Thilly and J. D. Embury, Advanced Engineering Materials (2004), 6, n°5, 290 Raabe, Mattissen: Acta Mater 46 (1998) 5973 7

10. Severe plastic co-deformation (SPD) of multiphase alloys (nano-scaled)

11. Wire drawing, ball milling, roll bonding, equal channel angular extrusion, high pressure torsion (of multiphase materials)

12. Very high interface density, dislocation density

13. Mechanical alloying, amorphization (against thermodynamic driving force)

14. Similar: frictional contact , friction stir welding, explosive joining

15. Understanding origin of strength in these material provides insight into modern alloy design based on complex solid solution phenomenaRaabe, Mattissen: Acta Mater 46 (1998) 5973 8

17. Severe plastic co-deformation (SPD) of multiphase alloys (nano-scaled)

18. Wire drawing, ball milling, roll bonding, equal channel angular extrusion, high pressure torsion (of multiphase materials)

19. Very high interface density, dislocation density

20. Mechanical alloying, amorphization (against thermodynamic potentials)

21. Similar: frictional contact , friction stir welding, explosive joining

22. Understanding origin of strength in these material provides insight into modern alloy design based on complex solid solution phenomena9

23. 10 1. Hall-Petch

24. 11 Strength pearlite observation: finerstructuresgivehigherstrength Embury and Fisher 1966

25. 12 StrengthCu-Nb observation: finerstructuresgivehigherstrength

26. 13 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

27. 14 2. High dislocationdensity

28. 15 Fibres; Cu-5 at.% Ag-3 at.% Nb (Cu-8.2 wt% Ag-4 wt% Nb) True strain: 10, Dislocation density ca. 5.0×1016m-2 Raabe, Ohsaki, Hono: Acta Mater. 57 (2009) 5254

29. 16 2. Amorphization

30. 17 Cu-Nb-Ag, 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 Raabe, Ohsaki, Hono: Acta Mater. 57 (2009) 5254

31. 18

32. 19 2. Mechanicalalloying

33. 20 Problem formulation: mechanically-driven alloying Systems: Tribosystems / contact mechanics; Heavy co-deformation Friction-based joining Possible reasons: Difffusion (requires thermodynamic driving force, negative mixing enthalpy) Interface thermodynamics (graded interfaces; surfactants / defactans - reducing interface energy through solutes) Gibbs–Thomson effect (size dependence of phase diagrams) Adiabatic temperature rise at interfaces Internal stresses Plasticity-assisted diffusion; pipe diffusion; pipe diffusion and break-away; Segregation and diffusion to dislocation cores in neighbor phase Deformation-induced increase in vacancy density Vortex formation (rotational shuffling) Dislocation shuffling ( n b ) Amorphization+trans-phase shear banding Raabe, Ohsaki, Hono: Acta Mater. 57 (2009) 5254

34. 21 Problem formulation: mechanically-driven alloying Howandwhy do materials mix across hetero-interfaces? Raabe, Ohsaki, Hono: Acta Mater. 57 (2009) 5254

35. 22 Fe-Cu alloy, ball milling Fe95Cu5 ; ball milling high-energyplanetary ball mill 20 h. Fe: green Cu: red O: blue

36. 23 Fibres; Cu-5 at.% Ag-3 at.% Nb (Cu-8.2 wt% Ag-4 wt% Nb) Nb phase Cu->40~60at% Nb->20~50at% Ag->5~28at% Raabe, Ohsaki, Hono: Acta Mater. 57 (2009) 5254

37. Pearlite, chemical composition and 3D reconstructed atom map Fe C 50 x 50 x 230 nm3, 13 millons ions 10 nm Top view 10 nm Front view Iso-concentrationvalue 7 at. % C 24

39. 26 Dislocationsatinterfaces Lecouturier F.Dupouy, E.Snoeck, M.J.Casanove, C.Roucau, J.P.Peyrade, S.Askénazy, Scripta.Mat, vol 34 (1996) n°7, 1067-1073

40. 27 Sauvage: Sharp steps in themechanicalalloyingprofile in Cu-V data: Xavier Sauvage, Rouen

41. 28 Sauvage: sharp steps in themechanicalalloyingprofile. pearlite data: Xavier Sauvage, Rouen

42. 29 AlN-CrN indented: steps in themechanicalalloyingprofile CrN AlN

43. 30 AlN-CrN indented: steps in themechanicalalloyingprofile CrN AlN

44. 31 Dislocation shuffling mechanism: mechanically-induced mixing Atomicscaleinterfaceroughening Raabe, Ohsaki, Hono: Acta Mater. 57 (2009) 5254

45. 32 Dislocation shuffling mechanism: mechanically-induced mixing Alternative: firstamorphizationand thenshearbandingacrossinterface

46. 33 Relationshipto ISMANAM topics? Modern alloy design based on complex solid solution phenomena Previousplenarytalks: Structureunitsandclusteridentification Thermodynamicunderstanding Correlationwithmechanicalproperties Structuralcorrelationlength in metallic glasses (shearzones) Fewatoms – fewnm Structuralcorrelationlength in ‘crystalline‘ metallic compounds (dislocations, transformations) Fewatoms – fewnm

47. 34 Relationshipto ISMANAM topics? When in heavily strained (crystalline) metallic compounds the interfaces become graded, semi-coherent, or dissolved, - where does the extreme strength come from ? Structuralcorrelationlength in metallic glasses (shearzones) Fewatoms – fewnm Structuralcorrelationlength in ‘crystalline‘ metallic compounds (dislocations, transformations) Fewatoms – fewnm

48. 35 Origin of high strength? Extreme solid solution effect: Dislocations move through: Mechanically alloyed high non-equilibrium fractions of solid solution Internal stresses High stored dislocation content Graded interface mechanics (?) Amorphous zones Similar correlation lengths as in bulk glasses (?) Shear bands Raabe, Ohsaki, Hono: Acta Mater. 57 (2009) 5254

49. 36 Conclusions regarding mechanical alloying in these systems Multiphase alloys can re rendered into ultra high strength bulk compounds by severe plastic co-deformation Phases turn into micro- and nano-scaled filaments At moderate and intermediate deformation the microstructure is characterized by a high interface density Strengthening is in this regime due to Orowan and Hall-Petch At high deformation strengthening is determined by interface dislocation reactions, heterophase dislocation penetration, and a high dislocation density. Typically in this strain regime deformation-driven intense chemical mixing (mechanical alloying) and atomic-scale structural transitions, e.g. amorphization, occur at the hetero-interfaces. For deformation-driven mixed systems with glass-forming characteristics (negative enthalpy of mixing) mechanical alloying and amorphization are considered to be associated phenomena. In mechanically mixed systems without the typical glass forming tendency structural transitions are attributed to the reduction of the high stored dislocation densities by amorphization. Among the various mechanisms suggested for massive mechanical alloying against the driving force trans-phase dislocation shuffling and shear banding is suggested : Multislip lattice dislocations penetrate the interfaces between abutting phases as a dominant process to induce deformation-driven chemical mixing. Heavily co-deformed multiphase materials offer an enormous potential for advanced alloy design. These materials already now represent the largest class of nano-structured bulk materials available today (for pearlite with yield strength beyond 5 GPa). Reason for high strength unclear