Laser-ultrasonics for metallurgy : overview and latest developments at NRC

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Laser-ultrasonics for metallurgy : overview and latest developments at

NRC

Laser-Ultrasonics for

Metallurgy:

Overview and Latest

developments at NRC

André Moreau, Daniel Lévesque (NRC) Sujay Sarkar (Arcelor Mittal)

1st_{International Workshop on LUMet}

Vancouver, November 13, 2013

Outline

• Introduction

• Temperature & Phase transformations

• Texture & recrystallization

• Grain size, recrystallization, grain growth

Recent work as illustrations. Collaboration with Sujay

Sarkar & Arcelor Mittal France.

Introduction

3

Laser-Ultrasonics for Metallurgy is:

• Ultrasonics

• applied to Metallurgy

• whereby ultrasound are generated and detected

with lasers

Detection laser Nd:YAG, 2 kW Gleeble 3500 TS Generation laser Excimer, 550 mJ, 15 ns Photorefractive Interferometer Laser windows Sample Optical Fibers Generation laser Nd:YAG, 400 mJ, 8 ns

Why laser-ultrasonics ?

• Penetrant radiations (bulk measurements):

• Neutrons

• High energy x-rays or

g

-rays

• Ultrasound: faster, safer, cheaper, easier, different

• In-situ, real-time

• Stress, strain, temperature, dilatometry

• Ultrasound: Elastic constants, scattering, internal friction

• Microstructure

• How the microstructure affects ultrasound is very well known.

• The inverse problem is more difficult, but no more difficult than

using other techniques such as stress relaxation or thermal

expansion.

5

What can be measured?

0 1 2

Time (µs)

Shear signal

Longitudinal signal

• Two basic information

• Time of arrival

• Amplitude

of the various echoes

Use mostly longitudinal

(pressure) waves

Everything affects the elastic constants

• Factor

relative change

• Material or Alloy 10-1

• Phase (solid vs. liquid, bcc vs. fcc, ferro vs. para magnetic) 10-1_{to 10}-2

• Crystallographic texture 10-2

• Temperature 10-4 _{/ °C}

• Stress 10-5 _{/ MPa}

• Internal friction mechanisms, including dislocations 10-3

• Porosity 10-1

• Grain size (frequency dependence or dynamic moduli) 10-2

• Laser-ultrasound measurement precision

10

-4

• Limited by signal-to-noise ratio

• Laser-ultrasound measurement accuracy

10

-3

• Limited by a variety of factors (thickness, temperature, diffraction, …)

7

Therefore

• Find the dominant effect:

• Aim to explain 90% of what you see

• The other 10% is going to be tough

• Build experiments where only one microstructural feature

changes at a time.

What microstructure information can be obtained?

9

• Time

If distance is known  Velocity

Velocity 

Elastic moduli

(v

2

_{= M/}



₎

 Chemistry



Phases & Porosity



Texture

 Residual stresses

 Internal friction (IF)

• Amplitude

If distance is known  Attenuation

Attenuation

 Diffraction

 nothing

 Scattering



Grain size

 Absorption (IF)  Dislocations

 Solid sol. elements

 Magnetic prop.

• Frequency dependence of elastic moduli and attenuation

are inter-related

Temperature & Phase transformations

Temperature: Near linear dependence

11 2.4 2.5 2.6 2.7 2.8 2.9 3 3.1 5.3 5.4 5.5 5.6 5.7 5.8 5.9 6 6.1 0 200 400 600 800 1000 1200 Sh e a r w a v e v e lo c it y k m /s ) Pre s s u re w a v e v e lo c it y (k m /s ) Temperature (°C)

Austenitic stainless steel

v2_{= M/}

In most cases:

Velocity and elastic constants vary almost linearly with temperature

50 55 60 65 70 75 80 130 140 150 160 170 180 190 200 0 200 400 600 800 1000 1200 Sh e a r m o d u lu s (M Pa ) Yo u n g 's m o d u lu s (G Pa ) Temperature (°C)

Notable exception: Magnetic materials

5 5.2 5.4 5.6 500 700 900 Temperature (°C) Heating Cooling T a-g T_Curie V e lo ci ty (km /s) Austenite Ferrite (non-magnetic) Ferrite (magnetic) 1006 Steel Non-linearity of ferrite below TCuriecaused by magnetism Kinks = Phase transformations

5500 5600 5700 5800 5900 6000 6100 6200 0 100 200 300 400 500 600 700 Tempe ra ture (C) L o n g it u d in a l v el o cit y ( m /s ) (Fe0.9Mn0.1)3C (Fe0.95Mn0.05)3C Fe3C

Another magnetic material: cementite (Fe

₃

C)

13 T_Curie Temperature (°C) V e lo ci ty (km /s)

In steels where cementite is present in large amounts, this anomaly can be superimposed onto the usual velocity curve of ferrite

Austenite decomposition

14 4.8 5 5.2 5.4 5.6 5.8 200 400 600 800 1000 Temperature (°C) V e lo ci ty ( km /s ) Pure a -Fe Pure g-Fe 5130 Pipe Steel

T

a-g

T

Curie

At fixed temperature, = Fraction of decomposed austenite

   v v v v  

Austenite decomposition of 5130 steel

Comparison between LUMet and dilatometry

15 0 0.2 0.4 0.6 0.8 1 1.2 0 200 400 600 800 Temperature (ºC) D e c o m p o s e d f ra c ti o n -5 °C/s dilatometry -5 °C/s laser-ultrasound -0.5 °C/s dilatometry -0.5 °C/s laser-ultrasound

Martensite  Austenite transformation in Stainless

Steel 415

2.6 2.7 2.8 2.9 3 3.1 3.2 0 200 400 600 800 1000 Temperature (C) R e d : L o n g . F re q . (M H z ) -0.4 -0.3 -0.2 -0.1 0 0.1 B lu e : D ila to m e te r (a rb . u n its ) Mart.  Aust. Mart.  Aust.

Martensite  Austenite transformation in Stainless

Steel 415

17 2.6 2.7 2.8 2.9 3 3.1 3.2 0 200 400 600 800 1000 Temperature (C) R e d : L o n g . F re q . (M H z ) -0.4 -0.3 -0.2 -0.1 0 0.1 B lu e : D ila to m e te r (a rb . u n its ) Mart.  Aust.

Mart.  Aust. Note:

Neither dilatometry nor ultrasound velocity come back to initial value

Probable explanation based on: Dilatometry: Artefact of measurement Ultrasound: Irreversible change in high temperature austenite

Dissolution and precipitation:

NbCN dissolution and precipitation in X80 steel

18 0.47 0.49 0.51 0.53 0.55 0.57 0.59 0 500 1000 1500 In ve rse T im e D e la y ( m s -1) Temperature (°C)

T

Curie

T

a _g

T

ga

T

NbCN -1.5 -1 -0.5 0 0.5 1 1.5 800 900 1000 1100 1200 1300 R e s id u a ls  1 0 0 0 ( m s -1) Temperature (°C) Deviation from linearity

Remarks

• Phase transformations are reversible

• Often appear as kinks in temperature dependence

• 1

st

_{order (with heat, allotropic) phase transformations}

show hysteresis in heating-cooling curve

• 2

nd

_{order phase transformation (magnetic) show no}

hysteresis in heating-cooling curve

19

Crystallographic orientation distribution (Texture)

Sound velocity is representative of the average texture.

Longitudinal velocities Shear velocities vFe<111>= 6453 m/s vFe<111>= 2997 m/s

vFe<110>= 6225 m/s vFe<110>= 3839 or 2470 m/s

vFe<100>= 5488 m/s vFe<100>= 3839 m/s

21

Lowest order texture coefficients (CODC) can be

measured with ultrasonics

• Well-established relationships between US velocity and

texture coefficients of order 4 or less.

22 W 4 0 0 (x 1 0 -3) u lt ra s o n ic s W 4 2 0 (x 1 0 -3) u lt ra s o n ic s W 4 4 0 (x 1 0 -3) u lt ra s o n ic s W420(x 10-3) diffraction W440(x 10-3) diffraction W400(x 10-3) diffraction

LUMet can measure 3 different velocities

23 e x3 x1 x2 S1 L S2 ) 2 5 ( 2 ) 2 ( 420 400 55 2 2 , 1 400 33 2 W W c C v cW C v S S L             

How to obtain the shear wave velocity

Method 1: Timing on shear

pulses

• Can sense variations only

• Cannot distinguish the 2

polarizations: Implies that

there is no additional texture

information to be gained

0 1 2 Time (µs) Shear signal Longitudinal signal A m p li tu d e ( a rb . u n it s ) ) 2 5 ( 2 ) 2 ( 420 400 55 2 2 , 1 400 33 2 W W c C v cW C v S S L             

How to obtain the shear wave velocity

• Method 2: Spectroscopy

25 0 5 10 15 20 Time (s) -1.2 -0.8 -0.4 0.0 0.4 0.8 A m p li tu d e ( a .u .) Time (m s) A m p li tu d e ( a rb . u n it s ) 2 4 6 8 10 12 Frequency (MHz) -60 -50 -40 -30 -20 -10 0 A m p litu d e ( d B ) 1S 1L 2L 3L 2S 3S 6S ) 2 5 ( 2 ) 2 ( 420 400 55 2 2 , 1 400 33 2 W W c C v cW C v S S L             

How to obtain the shear wave velocity

• Method 2: Spectroscopy

• Shear signal difficult to

optimize

• Never use 1

st

_{and 2}

nd

_order

resonances

• Beware of artefacts caused by

sample edges: Use wide

samples (5 cm in Gleeble)

• With 3 resonances, can solve

for thickness, W

400

, W

420 26 0 5 10 15 20 Time (s) -1.2 -0.8 -0.4 0.0 0.4 0.8 A m p li tu d e ( a .u .) Time (m s) A m p li tu d e ( a rb . u n it s ) 2 4 6 8 10 12 Frequency (MHz) -60 -50 -40 -30 -20 -10 0 A m p litu d e ( d B ) 1S 1L 2L 3L 2S 3S 6S ) 2 5 ( 2 ) 2 ( 420 400 55 2 2 , 1 400 33 2 W W c C v cW C v S S L             

Isothermal annealing of AA5754 at 325 °C

27

Symbols: laser-ultrasonic measurements on a single sample

Symbols + lines: neutron diffraction measurements on 7 quenched samples

3 4 5 6 7 1 10 100 1000 10000 Time (s) W 4 0 0 ( x 1 0 -3 ) -2 -1 0 1 2 W 4 2 0 ( x 1 0 -3 ) W400 Neutrons W420 Neutrons

Isothermal annealing of AA6111 at 350 °C

-4 -2 0 2 4 6 1 10 100 1000 10000 Time (s) W 4 0 0 ( x 1 0 -3 ) Ultrasound Neutrons

Symbols: LUMet measurements on a single sample

Austenite recrystallization in cold-rolled Fe-25%Ni

model alloy (recent work with Arcelor Mittal)

29 U lt ra so u n d ve lo ci ty (km /s) Time (min) Remarks:

Absolute velocity is not reliable because of thickness measurement

What is important is velocity change from initial to final state, i.e. from initial to final texture

Metallography (Arcelor Mittal)

30

Init ial (t0min) M iddle (t5min) End (t12min)

Hardness (Arcelor Mittal)

31

Recrystallized fraction

• Ultrasonically, the recrystallized fraction is the fractional

change of velocity from initial to final velocity

0 0.2 0.4 0.6 0.8 1 1.2 0.01 0.1 1 10 100 R e c ry s ta ll iz e d f ra c ti o n t/t  _t n RX

e

f



1



0.693 / i f i RX

v

v

v

v

f







US recrystallized fraction Model curve:

Fictitious US velocity data or Avrami eq.

Austenite recrystallization in cold-rolled Fe-25%Ni

model alloy (Arcelor Mittal)

33 -20 0 20 40 60 80 100 120 1 10 100 1000 R e c ry s ta ll iz e d fr a c ti o n ( % ) Time (sec) 675°C 700°C 725°C 750°C Time (s) R e cr yst a lli ze d f ra ct io n ( % )

Fit Avrami eq. to velocity data

Fitting Avrami equation... (Arcelor Mittal)

34 0 0.2 0.4 0.6 0.8 1 1.2 0.01 0.1 1 10 100 R e c ry s ta lli z e d fr a c ti o n t/t  _t n RX

e

f



1



0.693 / -2 0 0 2 0 4 0 6 0 8 0 10 0 12 0 1 10 10 0 1000 R e c ry s ta lli ze d fr a c ti o n (% ) Time (se c) 675° C 700° C 725° C 750° C Temperature (°C) ‘t ’ (s) ‘n’ 675 630 1.6 700 216 2.0 725 84 1.5 750 28.8 1.7

... to obtain Activation energy (Arcelor Mittal)

35

Acitvation energy from slope: Q = 326 kJ/mol y = 6 E-1 6e3 9 .2 5 5 x R² = 0.999 8 10 100 1 00 0 0.9 6 0.9 8 1.00 1 .02 1 .04 1.0 6 t h a lf ( s) 1000/ T (K-1₎ 1000/T (K-1₎ t (s)





RT

Q

Aexp





Combined temperature phase transformation

-recrystallization: Cold rolled A366 steel

• Phase transformations are reversible

• Recrystallization with texture change is not reversible

4.5 5 5.5 500 700 900 Temperature (°C) Heating Cooling 1s t cycle 3rd cycle 2nd cycle V e lo ci ty (km /s) TC T_a-g Curves are offset for clarity

Comment: What’s better ?

• What is the best way to estimate recrystallized fraction

• Hardness? • Objective

• Hard to interpret: Based on recrystallized grains being softer • Multiple quench samples, easy to measure

• Metallography? • Semi-objective

• Easy to interpret:Based on the definition of recrystallization • Multiple quench samples, hard to measure

• Ultrasound velocity change? • Objective

• Easy to interpret: Based on texture change • Single sample, no quench, easy to measure

37

Grains size, recrystallization, grain growth

Ultrasound attenuation

• Caused by either

• Diffraction

• Scattering by grains

• Absorption = Internal friction (multiple causes)

• Diffraction

• Minimize its effects • Or make it constant

• Can’t tell scattering from absorption in the Gleeble

• Steel: Mostly scattering

• Aluminium: Internal friction and scattering

39

How attenuation spectra are measured

Ratio of amplitude spectra

1st echo A 2nd echo Amplitude spectra FFT FFT f

M at erial being measured Reference mat erial

A (f) Aref(f)         ) f ( A ) f ( Aref log e 2 20 ) f ( 10 Frequency (MHz) 0 2 4 6 8 10 12 14 16 18 20 A tt en u at io n ( d B /m m ) 0 0 .1 0 .2 0 .3 0 .4 0 2 4 6 8 10 12 14 16 18 0 1 2 3 4 Frequency (MHz) A tt e n u a ti o n ( d B /m m )

Ultrasonic attenuation (scattering) is a measure of grain

size

41

0

100

200

0

2

4

6

1008 1020 1035 1074 A36

Au

st

en

ite

G

ra

in

Si

ze

(µ

m

)

Ultrasonic Attenuation at 15 MHz (dB/mm)

AISI grade

AISI 304 Stainless steel

42 Grains sizes ASTM m m n 5 56 2.1 8 20 2.7 10 10 3.3 0.01 0.1 1 10 100 10 100

Frequency (MHz), log scale

A tt e n u a ti o n ( d B /m m )

Grain size measurement works well for kd < 2, n  3

43 0.01 0.1 1 10 100 10 100

Frequency (MHz), log scale

A tt e n u a ti o n ( d B /m m ) 0.001 0.01 0.1 1 0.1 1 10

kd

(dimension-less)

a

/k

(d

B

)





 

1 1 1 1

2

   









n n n n n n n

kd

k

k

d

d

f

d













n - 1 = 2

In practice

• n varies slowly and is hard to measure accurately

• It is best to set n = constant

• n = 3 works well

• There is a temperature effect:

• Don’t worry about kd < 2:

• At too high a frequency, attenuation is too high and there is no

signal left

3 2

)

(

T

d

f

C





 

2

)

(

T

kd

C

k





Timken CTMP project

45

Hot tube

1000  C

Sensor

Head

Umbilical cord

to lasers and

interferometer

Tube reducing

Machine

Timken CTMP project calibration is used by LUMet software

& used for all austenite grain size measurements

46 0 0.5 1 1.5 2 2.5 0 50 100 150 200 250 300 Grain size (m) F it te d p a ra m e te r: b 1 /2 Frequency (MHz) 0 2 4 6 8 10 12 14 16 18 20 A tt en u at io n ( d B /m m ) 0 0 .1 0 .2 0 .3 0 .4 0 2 4 6 8 10 12 14 16 18 0 1 2 3 4

Austenite grain growth

(Arcelor Mittal)

47

DP: 0.11C, 1.9Mn, 0.35Cr, 0.3Si

Deep drawing: 0.04C, 0.23 Mn _{Micro-alloyed (Nb and Ti)}

Lines: Laser-ultrasonics, 2 different references Symbols: Metallography on

quenched samples

Recovery & recrystallization following hot mechanical

deformation

Strain applied here (rate of 1/s)

Laser-ultrasonic measurements

CP steel transfer bars: Effect of applied strain on

recovery, recrystallization, grain growth

49

Lines: LUMet data

Symbols: 5% and 95% recrystallization as predicted by metallurgical model

Recovery & crystallization following hot mechanical

deformation: Effect of applied strain (Arcelor Mittal)

50 Deep drawing Dual phase mAlloyed (Ti, Nb) 850 °C e = 0.22 Deep drawing Dual phase mAlloyed (Ti, Nb) 850 °C e = 0.22 Rx start

Recovery & crystallization following hot mechanical

deformation: Effect of applied strain (Arcelor Mittal)

51 Deep drawing Dual phase mAlloyed (Ti, Nb) 850 °C e = 0.22 Deep drawing Dual phase mAlloyed (Ti, Nb) 850 °C e = 0.22 Deep drawing Dual phase mAlloyed (Ti, Nb) 850 °C e = 0.75 Deep drawing Dual phase mAlloyed (Ti, Nb) 850 °C e = 0.75 Rx start

Recovery & crystallization following hot mechanical

deformation: Effect of temperature & strain (Arcelor Mittal)

m alloyed (Ti, Nb) 850 °C, e = 0.22 850 °C, e = 0.75 1050 °C, e = 0.22 1050 °C, e = 0.75 Rx start

Onset of grain growth Hump can mislead into thinking there is recrystallization

Remarks

• We can always calculate a grain size from ultrasonic

attenuation data, even when it does not make sense!

• ± Same applies to metallographic techniques

• Calibration valid for fully recrystallized, equiaxed grains, with

“log-normal” distribution of grain sizes

• Accuracy

• Hard to estimate

• Seems comparable to metallographic work

• Check with limited number of metallographic samples

• Precision

• Ability to monitor changes is better than metallographic work

• Repetition rate up to 10 Hz

53

Conclusion

• LUMet technology is well-established for

• Elastic constants

• Phase transformations

• Texture and recrystallization

• Austenite grain size, grain growth, and recrystallization

• LUMet technology has room to grow

• Effect of grain shape

• Dislocations, recovery

• Metals other than steels, nickel, and aluminium

55 55

Thank you

André Moreau

Senior Research Officer Tel: 450-641-5237

[email protected] www.cnrc-nrc.gc.ca