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Microstructure and Properties of Engineering Materials

Helmut Clemens and Svea Mayer

Department of Physical Metallurgy and Materials Testing

Montanuniversität Leoben, Roseggerstraße 12, 8700 Leoben, Austria

helmut.clemens@unileoben.ac.at

presented by

Peter Staron

Institut für Werkstoffforschung, Helmholtz-Zentrum Geesthacht

Application of Neutron and Synchrotron Radiation in Engineering Materials Science

1 m 1 km 10000 km 1Mio. km10 cm

nanotechnology nano/microstructure component

1 Å 1 nm 100 nm 1 µm 100 µm 1 mm 1 cm 1 m

Dimensions in materials science

2

Bonding

Engineering materials

• metallic shining• excellent electrical and thermal conductivity• good deformability

“The (R)Evolution of engineering materials

Intermetallics

3

Microstructure of metallic materials

- phase (fcc)

- phase (bcc)

Mutual solubility!

Microstructure & strength of metallic materials

growth of pores

grain boundary sliding

Low temperature (T < 0.3·TM) High temperature (T > 0.3·TM)

dispersion

solid solution

precipitation

deformation

climb (dislocationcreep)

fine grain

recovery & recrystallisation

diffusional creep

4

Microstructural parameters

dislocation density:

grain size:

subgrain/domain size:

concentration of alloying elements:

size and volume fraction of particles: (precipitates, dispersoids)

1010 – 1016 m-2

nm – dm range

nm – µm

ppm – 50%

nm – µm range,0 – 70%

phase morphology and arrangement

The following microstructural parameters determine the properties of engineering (metallic) materials:

Arrangement of the specific constituents MICROSTRUCTURE

-ferrite (bcc) + cementite (Fe3C)

martensite (distorted bcc lattice)

Example: plain carbon steel

residual stresses due to martensitic

transformation

Microstructure & strength

5

HRTEM

Microstructure & deformation behaviour

Plastic deformation corresponds to the motion of dislocations in response to an applied shear stress!Plastic deformation corresponds to the motion of dislocations in response to an applied shear stress!

A dislocation is a crystalline defect

Microstructure & deformation behaviour

superplasticity

fcc lattice

(Cu, Al, Ni)

hex lattice

(Mg, -Ti)

0211}0001{ 011}111{

slip plane

slip direction

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Texture

x

y

pole figure

x

y

z

no texture isotropic mechanical properties

x

y

x

y

z

strong texture anisotropic mechanical properties

x

y

“cube” texture

Texture

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Textures in engineering materials: pros & cons

Iron Nickel

Steel

Formation of texture

cold – working hot – working annealing

10 µm

8

Recovery and recrystallisation

Recrystallisation

Recovery

10 µm

deformed state annealed state

Mechanisms of recovery

Polygonisation and subsequent growth of subgrains

10 µm

subgrains in Al

Interstitial atoms diffuse to vacancies

Annihilation of dislocations showing opposite signs

Condensation of vacancies

Formation of subgrains(polygonisation). Reduction of dislocation energy

9

Recrystallisation

Brass(Cu-Zn alloy)

cold-worked (33%)

580°C/3sec

580°C/4sec 580°C/8sec

In-situ deformation experiment

Synchrotron radiation storage ring with bending magnets → high energy X-rays

Sample

Detector (image plate or CCD)

Monochromator

Deformation device

Temperature

Force

Time

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Debye-Scherrer rings of a three-phase TiAl alloy

Ti-43Al-4Nb-1Mo-0.1B (at%)

o

/2

In-situ – investigation using synchrotron radiation

In-situ deformation experiment

11

XRD patterns ↔ microstructure

Response of patterns on processing

Response of patterns on processing

deformation & temperature

XRD patterns ↔ microstructure

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Microstructure after thermo-mechanical processing

Precipitation hardened Fe - Co - Mo steel

Fine secondary - phasenot visible

Martensitic matrix

(Fe - Co - Mo)

Coarse secondary - phase

(Fe,Co)7Mo6

Precipitation hardening

3 x 1h

Example: ordinary and and advanced tool steels

3 x 1h

homogeneous solid solution

coherent precipitates

Particle coarsening

“Oswald ripening”

loss of coherency

3P tr

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Information on: ● crystal structure

● chemical composition

● particle size

● interface structure

electron source

condensor lenses

objective lens

specimen

projective lens

eye

light microscope

viewing screen

negative plates or camera

isolator

Transmission Electron Microscopy

Characterization of precipitates

Transmission electron microscopy (TEM)

Example: Advanced steel based on Fe-Co-Mo

Conventional TEM

Coarse secondary - phase

(Fe,Co)7Mo6

High-resolution TEM

Fine secondary - phase

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3D - atom probe (3DAP)

high voltage

Pulsecommand

time of flightmeasurement

impact location

20 to 100 K

3 to 15 kV

X

Y

2

2ges

d

tVe2

n

m

Characterization of nm-sized precipitates

Information on: ● chemical composition

● volume fraction

● particle size

r ~ 50nm

samplefield evaporation

Example: Advanced steel based on Fe-Co-Mo

Intermetallic -(Fe,Co)7Mo6

precipitates

Martensitic matrix

(Fe - Co - Mo)

Three-dimensional atom probe

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Small-angle neutron scattering (SANS)

Information on: ● particle size distribution (1–100 nm)

● volume fraction

large sample volume

no direct information

mag.+ nuc.

nuc.

H

SANS beamline assembly:

Example: Advanced steel based on Fe-Co-Mo

0,1 110-2

10-1

100

101

102

103

540°C615°C675°C

d/d

[cm

–1sr

–1]

q [nm–1]

0 5 10 150,00

0,02

0,04

0,06

0,08

0,10

0,12 540 °C 615 °C 675 °C

f (R

) [n

m–

1]

R [nm]

SANS curves and size distributions

Evolution of the fine -(Fe,Co)7Mo6

precipitates with ageing temperature

(and time)

Small-angle neutron scattering (SANS)

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Tem

pera

ture

[°C

]

1000

1100

1200

1300

1400

1500

1600

36 40 44 48 52 56

Aluminium [Atomic-%]

+

2

2 +

L

Evolution of a fully lamellar microstructure

Example:

Evolution of a fully lamellar microstructure

Phase transformations

→

+

2

2 +

L

Tem

per

atu

re [

°C]

1000

1100

1200

1300

1400

1500

1600

36 40 44 48 52 56

Aluminium [At%]

-Tr

ansu

s Li

ne

Information on: ● phase transformations

● thermal expansion coefficient

● in-situ deformation studies

Volume change due to phase transformation

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In-situ – investigation using synchrotron radiation

Debye-Scherrer-cone

sample

high-energy X-ray beam

detectors

2

0

Time

2 /2Precipitation of -TiAl lamellae

(d) (e)

Phase diagrams & phase fractions

Calculated phase diagram

The corresponding diffraction pattern are analyzed by Rietveld methodThe corresponding diffraction pattern are analyzed by Rietveld method

Information on:

● occurring phases and their volume fractions

● phase transformations

● phase transition temperatures

● kinetics of phase transformations

● order/disorder reactions

● …….

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Ordering behaviour

Structure Powder Diffractometer (SPODI) at FRM II in Munich, Germany λ = 1.55 Å.

sin

4

q

Ti-43.9-Al-3.8Nb-1Mo-0.1B (at%)

Scattering lengths:

bAl ~ -bTi

→ in-situ neutron diffraction

In TiAl-based alloys only reflections of orderedphases are visible!In TiAl-based alloys only reflections of orderedphases are visible!

?

Ordering/disordering behaviour → in-situ neutron diffraction

Heating rate: 10 Kmin-1

Loss of order in the o-phase is indicated by a sharp drop in intensity of the corresponding reflection

Loss of order in the o-phase is indicated by a sharp drop in intensity of the corresponding reflection

To

rd

1225

°C

Two-axes powder diffractometer (WOMBAT) at ANSTO in Menai, Australia.λ = 1.67 Å.

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Summary

Important information needed:● grain/subgrain/domain size

● crystal structure and chemistry

● preferred grain orientation (texture)

● 3-dimensional arrangement of phases

● phase transitions (onset, temperatures...)

● size and volume fraction of particles(precipitates, dispersoids)

● structure and type of appearing interfaces

● types of defects and defect density (pores, cracks…)

● vacancy concentration and dislocation density

● local/residual stresses

● microstructural evolution during deformation and/or thermal treatment

● nucleation and growth processes

● order/disorder reactions….

References and Acknowledgements

References & further reading:

W.D. Callister Jr., Materials Science and Engineering - An Introduction,

John Wiley & Sons

T.H. Courtney, Mechanical Behavior of Materials, McGraw - Hill

M.F. Ashby and D.R.H. Jones, Engineering Materials, Vols. 1 & 2, Pergamon Press

R.E. Smallman and R.J. Bishop, Modern Physical Metallurgy & Materials

Engineering, Butterworth - Heinemann

M.F. Ashby, Materials Selection in Mechanical Design, Pergamon Press

G. Gottstein, Physikalische Grundlagen der Materialkunde, Springer Verlag

W. Reimers, A.R. Pyzalla, A. Schreyer, and H. Clemens (Editors),

Neutron and Synchrotron Radiation in Engineering Materials Science,

WILEY-VCH

Special Issue: Advanced Engineering Materials 13 (2011) 635-850.

Valuable contributions of the following persons are gratefully acknowledged:

Christina Scheu, Peter Staron, Andreas Stark, Andreas Schreyer, Klaus-Dieter Liss, Arno Bartels, Heinz-Günter Brokmeier, Gerhard Dehm, Thomas Schmölzer, Martin Schloffer, Emanuel Schwaighofer, Elisabeth Eidenberger, Michael Schober, .…