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Atomic-scale mechanisms in mechanical alloying

D. Raabe, Y.J. Li, P. Choi, X. Sauvage*, R. Kirchheim**, K. Hono***

Düsseldorf, [email protected]

ISMANAM Conference 8, July 2010 ETH Zürich

Towards the limits of strength in ductile nano-structured bulk materials

* Physique des Matériaux, University Rouen, France** Max-Planck-Institut and Physics Dpt. University Göttingen, Germany*** NIMS, Japan

Thanks to: R. Pippan, J. D. Embury

Overview

Introduction to nanostructured crystalline multiphase bulk alloys with extreme strength

Mechanical alloying

Example # 1– key mechanisms: Maraging - TRIP

Weight reduction( - 300 kg )

1.5 GPa-steels: Maraging-TRIP steels: Fe 12-15 % Mn Ni Al Ti

Raabe et al. Scripta Mater 60 (2009) 1141 3

Weight reduction( - 300 kg )

1.5 GPa-steels: Maraging-TRIP steels: Fe 12-15 % Mn Ni Al Ti

4Raabe et al. Adv. Eng. Mater. 11 (2009) 547

Example # 1– key mechanisms: Maraging - TRIP

Ultra high strength and corrosion resistance

2 GPa-steels: Aged martensite: Fe 13 Cr > 0.3 C

5steel research int. 79 (2008) No. 6

1.5 K/s (slab) 4000 K/s (strip)

Example # 2– key mechanisms: Martensite relaxation and aging

2 GPa-steels: Aged martensite: Fe 13 Cr > 0.3 C

γα‘

carbide

carbon

6steel research int. 79 (2008) No. 6

Example # 2– key mechanisms: Martensite relaxation and aging

> 5 GPa-steels: Pearlite: nanostructured and mechanically alloyed

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).

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Example # 3– key mechanisms: Nanostructures

Raabe, Mattissen: Acta Mater 46 (1998) 5973

> 2 GPa- Cu-alloys: Cu-Nb, Cu-Nb-Ag : nanostructured and mechanically alloyed

taken from K. Spencer, F. Lecouturier, L. Thilly and J. D. Embury, Advanced Engineering Materials (2004), 6, n°5, 290

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Example # 4– key mechanisms: Nanostructures

Strongest ductile nano-structured bulk materials available: pearlite, Cu-Nb, Cu-Ag (simple), QP martensite

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

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

Very high interface density, dislocation density

Mechanical alloying, amorphization (against thermodynamic driving force)

Similar: frictional contact , friction stir welding, explosive joining

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

Focus on the last 2 examples: co-deformed composites

9Raabe, Mattissen: Acta Mater 46 (1998) 5973

Strongest ductile nano-structured bulk materials available: pearlite, Cu-Nb, Cu-Ag (simple), QP martensite

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

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

Very high interface density, dislocation density

Mechanical alloying, amorphization (against thermodynamic potentials)

Similar: frictional contact , friction stir welding, explosive joining

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

More specific

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1. Hall-Petch

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Strength pearlite

observation: finer structures give higher strength

Embury and Fisher 1966

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0 2 4 6 8 10 12wire deformation

200

400

600

800

1000

1200

1400

1600

1800

2000

2200u

ltim

ate

ten

sile

str

engt

h [

MP

a]Do= 1,4µm Cu-8.2 wt%Ag-4 wt%NbDo= 6,2µm Cu-20 wt%Nb (Spitzig et al.)Do= 3,8µm Cu-20 wt%Nb (Spitzig et al.)

Strength Cu-Nb

observation: finer structures give higher strength

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h=7.5 h=8.6 h=10.0

Fibres; Cu-5 at.% Ag-3 at.% Nb (Cu-8.2 wt% Ag-4 wt% Nb)

Raabe, Ohsaki, Hono: Acta Mater. 57 (2009) 5254

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2. High dislocation density

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True strain: 10,Dislocation density ca. 5.0×1016m-2



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2. Amorphization

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Cu-Nb-Ag, h=10.0 Nb phase

Amorphization at Cu/Nb interface

see also: X.Sauvage: University of Rouen

D. 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) 30503061


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2. Mechanical alloying

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Problem formulation: mechanically-driven alloying


Systems: a) Tribosystems / contact mechanics; b) Heavy co-deformationc) Friction-based joining

Possible reasons:d) Difffusion (requires thermodynamic driving force, negative mixing enthalpy)e) Interface thermodynamics (graded interfaces; surfactants / defactans - reducing

interface energy through solutes)f) Gibbs–Thomson effect (size dependence of phase diagrams)g) Adiabatic temperature rise at interfacesh) Internal stressesi) Plasticity-assisted diffusion; pipe diffusion; pipe diffusion and break-away;

Segregation and diffusion to dislocation cores in neighbor phasej) Deformation-induced increase in vacancy density k) Vortex formation (rotational shuffling)l) Dislocation shuffling ( n b )m) Amorphization+trans-phase shear banding

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Problem formulation: mechanically-driven alloying


How and why do materials mix across hetero-interfaces?

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Fe-Cu alloy, ball milling

Fe95Cu5 ; ball millinghigh-energy planetary ball mill 20 h. Fe: greenCu: redO: blue

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Cu→40~60at%Nb→20~50at%Ag→5~28at%

Nb phase



Fe

C

Iso-concentration value 7 at. % C

Pearlite, chemical composition and 3D reconstructed atom map

Front view

Topview

10 nm

10 nm

50 x 50 x 230 nm3, 13 millons ions

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1. Large amount of C dissolved in ferrite

2. Inhomogeneous distribution of C

3. ε < 5, carbon concentration increases with wire strain

4. ε > 5, carbon concentration appears to saturate.

CementiteFerrite

Carbon concentration as fct. of lamellar thickness

Mechanisms of decomposition:

Carbon-dislocation interactions

Destabilization due to the increase of free energy

(0.5~1) eV between C and dislocation

(0.4~0.42) eV between C and Fe in Fe3C

Binding energy

As-patented

Pearlite, chemical composition as a function of strain and size

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

Lecouturier

Dislocations at interfaces

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data: Xavier Sauvage, Rouen

Sauvage: Sharp steps in the mechanical alloying profile in Cu-V

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data: Xavier Sauvage, Rouen

Sauvage: sharp steps in the mechanical alloying profile. pearlite

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AlN-CrN indented: steps in the mechanical alloying profile

CrNAlN

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AlN-CrN indented: steps in the mechanical alloying profile

CrNAlN

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Dislocation shuffling mechanism: mechanically-induced mixing

Atomic scale interface roughening


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Dislocation shuffling mechanism: mechanically-induced mixing

Alternative: first amorphization and then shear banding across interface

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Relationship to ISMANAM topics?

Modern alloy design based on complex solid solution phenomena

Previous plenary talks:

Structure units and cluster identificationThermodynamic understandingCorrelation with mechanical properties

Structural correlation length in metallic glasses (shear zones)Few atoms – few nm

Structural correlation length in ‘crystalline‘ metallic compounds (dislocations, transformations)Few atoms – few nm

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Structural correlation length in metallic glasses (shear zones)Few atoms – few nm

Structural correlation length in ‘crystalline‘ metallic compounds (dislocations, transformations)Few atoms – few nm

When in heavily strained (crystalline) metallic compounds the interfaces become graded, semi-coherent, or dissolved,

- where does the extreme strength come from ?

Relationship to ISMANAM topics?

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Extreme solid solution effect:

Dislocations move through:Mechanically alloyed high non-equilibrium fractions of solid solutionInternal stressesHigh stored dislocation contentGraded interface mechanics (?)Amorphous zonesSimilar correlation lengths as in bulk glasses (?)

Shear bands

Origin of high strength?


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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 densityStrengthening 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

Conclusions regarding mechanical alloying in these systems

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