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1
RECRYSTALLIZATION IN METALS
FLORENT LEFEVRE-SCHLICK and DAVID EMBURY
Department of Materials Science and Engineering
McM...
2
OUTLINE
 Recrystallization
What is it?
How is it usually treated?
Importance of local misorientation/strain gradients o...
3
What is it?
Fe
E =Estored=~100J/mol
Deformation
Heat
Recovery
(rearrangement of dislocations in sub grains)
Recrystalliz...
4
Recrystallization
HOW DOES RECRYSTALLIZATION START?
 “nucleation”
 Strain Induced
Boundary Migration
∆Θ1
∆Θ2
∆Θ3
∆Θ4
∆...
5
Improving the mechanical properties of materials
 How does recrystallization proceed?
 How to control recrystallizatio...
6
Johnson, Mehl, Avrami, Kolmogorov approach
1 exp( )n
X Bt= − −
0
1
recrystallizedfractionX
time
 Random distribution of...
7
Johnson, Mehl, Avrami, Kolmogorov approach
Recrystallization
Is n misleading?
<1Fe-Mn-C
1.7Aluminium+ small amount of co...
8
“NUCLEATION” OF RECRYSTALLIZATION
Recrystallization
Hu et al. (1966) Adcock et al. (1922)
Large orientation gradient
(tr...
9
Particle Stimulated Nucleation
Leslie et al. (1963) Humphreys et al. (1977)
Oxide inclusions in Fe Al-Si system Cluster ...
10
INVESTIGATING THE “NUCLEATION” EVENT
 Injecting nucleation sites to increase N:
• Local misorientation (twins)
• Local...
11
What are rapid heat treatments?
T
time
•“Slow” heat treatment
(salt bath)
•“Rapid” heat treatment
(spot welding machine...
12
“Slow” heat treatment: Salt bath
Time/Temperature profile during salt bath
heat treatment
0
100
200
300
400
500
600
700...
13
“NUCLEATION” IN IRON
Fe deformed by impact at 77K
50 µm B=[011]
01-1 -21-1
-200
21-1
-2-11
2-22
(-2-11)
(1-11)
grain
tw...
14
ZA=[011]
ZA=[113] ZA=[113]
ZA=[113]
200
0-11
22-2 21-1
ZA=[133]
-110
0-31
12-1
-301
21-1
-110
0-31
12-1
-301
21-1
-110
...
15
“NUCLEATION” IN COPPER
50 µm
1 µm 4 µm
25 µm
Cu 60% cold rolled Cu ~ 2% recrystallized
5 seconds at 250o
C
No noticeabl...
16
45% cold rolled @ 77K
100µm
Stainless steel 316L
Cooperation with X. Wang
Salt bath
“NUCLEATION” IN STAINLESS STEEL
17
2 min @ 950C
25µm
Stainless steel 316L
Average grain size: 7µm
Salt bath
“NUCLEATION” IN STAINLESS STEEL
18
25µm
2 min @ 900C
Stainless steel 316L
Average grain size: 5µm
Salt bath
“NUCLEATION” IN STAINLESS STEEL
19
Stainless steel 316L
25µm
2 min @ 850C
Average grain size: 3µm
Salt bath
“NUCLEATION” IN STAINLESS STEEL
20
1 min @ 800C
10µm
Role of annealing, deformation twins and phases on nucleation and growth?
Stainless steel 316L
Salt b...
21
DF image (austenite)
DF image
(austenite + martensite)
DF image (Twin)
BF image
Salt bath
1 min @ 800C
Stainless steel ...
22
Salt bath
Stainless steel 316L, 2 min @ 850C
25µm
RECRYSTALLIZATION AS A WAY TO CONTROL THE NATURE
OF GRAIN BOUNDARIES?...
23
“RAPID” HEAT TREATMENT: SPOT WELDING MACHINE
3mm
250 µm
Fe annealed (thickness = 500 µm)
Fe 60% cold rolled (thickness ...
24
PHASE TRANSITION IN IRON
50 µm 50 µm
40 J 20 J
Melted zone
Heated zone
 Refinement of the microstructure via phase tra...
25
RECRYSTALLIZATION AND PHASE TRANSITION IN IRON
40 J
50 µm100 µm
 Refinement of the microstructure via phase transition...
26
20 J
50 µm
 Localized event along specific grain boundaries
Spot welding machine
RECRYSTALLIZATION AND PHASE TRANSITIO...
27
Laser pulse:
 Energy (nJ to µJ)
 Time (fsec to nsec)
 Beam size (µm to mm)
Small volume on the surface
 Rapid heati...
28
 λ = 800 nm
 The beam has a Gaussian profile
with a radius ω0
 E0: full energy pulse (~10 µJ)
 τp: duration of the ...
29
WHY PULSED LASERS?
Pulse lasers
30
SINGLE PULSE ABLATION OF FE
E = 9.2 µJ
10 µm
5 µm
E = 1.0 µJ
10 µm
E = 3.2 µJ
5 µm
E = 0.2 µJ
 What is the temperature...
31
Si substrate
SiO2 isolant layer
Platinum
2 mm
2 mm 100 µm
25 nm2 µm
resistor
connector
TEMPERATURE MEASUREMENT DEVICE
S...
32
Fe annealed, 1 grain
Corrected harmonic contact stiffness: 1.106
N/m
0
10
20
30
200 400 600 800 1000 1200
Load On Sampl...
33
1 2 3
12 11 10
-1
0
1
2
3
4
5
6
7
100 200 300 400
Load On Sample (mN)
Displacement Into Surface (nm)
1
2
3
4
5
6
7
8
[9...
34
SGGrain I
Grain II
nucleus
Grain I
Grain II
)(
2
)(
tr
tG
γ
>
Modeling
ZUROB’S MODEL FOR RECRYSTALLIZATION
 Needs inpu...
35
CONCLUSIONS – FUTURE WORK
 Investigation of the first stage of recrystallization by:
o Designing microstructures to pr...
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702 florent lefevre-schlick_november_2005

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702 florent lefevre-schlick_november_2005

  1. 1. 1 RECRYSTALLIZATION IN METALS FLORENT LEFEVRE-SCHLICK and DAVID EMBURY Department of Materials Science and Engineering McMaster University, Hamilton, ON, Canada
  2. 2. 2 OUTLINE  Recrystallization What is it? How is it usually treated? Importance of local misorientation/strain gradients on “nucleation” First stages of recrystallization; how can we investigate the “nucleation”?  Rapid heat treatments What are they? What can we expect from them? Recrystallization in metals  Modeling  Conclusions-Future work
  3. 3. 3 What is it? Fe E =Estored=~100J/mol Deformation Heat Recovery (rearrangement of dislocations in sub grains) Recrystallization (development of new strain free grains) Recrystallization
  4. 4. 4 Recrystallization HOW DOES RECRYSTALLIZATION START?  “nucleation”  Strain Induced Boundary Migration ∆Θ1 ∆Θ2 ∆Θ3 ∆Θ4 ∆Θ1 ∆Θ3 ∆Θ4 Θ1 Θ2 Θ1 Θ2 Θ2 E 1 E 2> Coalescence and growth of subgrains Migration of a boundary In simple systems: small number of “nuclei” lead to recrystallized grains
  5. 5. 5 Improving the mechanical properties of materials  How does recrystallization proceed?  How to control recrystallization?  How to achieve an important grain refinement?  Can we control more than just the scale? 0 1000 2000 3000 4000 5000 6000 7000 0 2 4 6 8 10 d -1/2 (µm -1/2 ) σY(MPa) Cu Fe Al Recrystallization Grain refinement strengthening
  6. 6. 6 Johnson, Mehl, Avrami, Kolmogorov approach 1 exp( )n X Bt= − − 0 1 recrystallizedfractionX time  Random distribution of nucleation sites  Constant rate of nucleation and growth n=4  Site saturation n=3 Recrystallization
  7. 7. 7 Johnson, Mehl, Avrami, Kolmogorov approach Recrystallization Is n misleading? <1Fe-Mn-C 1.7Aluminium+ small amount of copper, 40% cold rolled 4Fined grained Aluminium, low strain 4/3/2Constant nucleation rate 3d/2d/1d 3/2/1Site saturation 3d/2d/1d
  8. 8. 8 “NUCLEATION” OF RECRYSTALLIZATION Recrystallization Hu et al. (1966) Adcock et al. (1922) Large orientation gradient (transition bands) Strain heterogeneities (shear bands) Fe-Si system Cu
  9. 9. 9 Particle Stimulated Nucleation Leslie et al. (1963) Humphreys et al. (1977) Oxide inclusions in Fe Al-Si system Cluster of SiO2 in Ni  Recrystallization originates at pre-existing subgrains within the deformation zone  Nucleation is affected by particle size and particle distribution “NUCLEATION” OF RECRYSTALLIZATION Recrystallization
  10. 10. 10 INVESTIGATING THE “NUCLEATION” EVENT  Injecting nucleation sites to increase N: • Local misorientation (twins) • Local strain gradient (high deformation) Recrystallization o  Impeding growth of recrystallized grains • Rapid heat treatments
  11. 11. 11 What are rapid heat treatments? T time •“Slow” heat treatment (salt bath) •“Rapid” heat treatment (spot welding machine) •“Ultra-fast” heat treatment (pulsed laser) T time T time seconds mseconds nano/pico/femtoseconds Rapid heat treatments
  12. 12. 12 “Slow” heat treatment: Salt bath Time/Temperature profile during salt bath heat treatment 0 100 200 300 400 500 600 700 0 5 10 15 Time (sec) Temperature(C) Duration of the heat treatment: 5 seconds. Temperature range: 500o C to 650o C. Heating rate ~300C/sec Cooling rate ~1000C/sec Salt bath
  13. 13. 13 “NUCLEATION” IN IRON Fe deformed by impact at 77K 50 µm B=[011] 01-1 -21-1 -200 21-1 -2-11 2-22 (-2-11) (1-11) grain twin Twinning plane {112} Shear direction 111 Production of deformation twins to promote a variety of potential nucleation sites for recrystallization, either at twin/grain boundary or twin/twin intersections 4 µm Salt bath
  14. 14. 14 ZA=[011] ZA=[113] ZA=[113] ZA=[113] 200 0-11 22-2 21-1 ZA=[133] -110 0-31 12-1 -301 21-1 -110 0-31 12-1 -301 21-1 -110 0-31 12-1 -301 21-1 Kikuchi patterns of the parent grain, a twin and a cell of dislocations. Shift of about 0.5 deg in the ZA between the grain (green circle) and the cell (red circle). -301 -310 5 seconds at 500o C BF images of a nuclei along a deformed twin. Salt bath “NUCLEATION” IN IRON
  15. 15. 15 “NUCLEATION” IN COPPER 50 µm 1 µm 4 µm 25 µm Cu 60% cold rolled Cu ~ 2% recrystallized 5 seconds at 250o C No noticeable effect of annealing twins on nucleation Salt bath
  16. 16. 16 45% cold rolled @ 77K 100µm Stainless steel 316L Cooperation with X. Wang Salt bath “NUCLEATION” IN STAINLESS STEEL
  17. 17. 17 2 min @ 950C 25µm Stainless steel 316L Average grain size: 7µm Salt bath “NUCLEATION” IN STAINLESS STEEL
  18. 18. 18 25µm 2 min @ 900C Stainless steel 316L Average grain size: 5µm Salt bath “NUCLEATION” IN STAINLESS STEEL
  19. 19. 19 Stainless steel 316L 25µm 2 min @ 850C Average grain size: 3µm Salt bath “NUCLEATION” IN STAINLESS STEEL
  20. 20. 20 1 min @ 800C 10µm Role of annealing, deformation twins and phases on nucleation and growth? Stainless steel 316L Salt bath “NUCLEATION” IN STAINLESS STEEL
  21. 21. 21 DF image (austenite) DF image (austenite + martensite) DF image (Twin) BF image Salt bath 1 min @ 800C Stainless steel 316L  Fine and complex deformed microstructure  Over a range of possible growing grains, only a few seem to grow “NUCLEATION” IN STAINLESS STEEL
  22. 22. 22 Salt bath Stainless steel 316L, 2 min @ 850C 25µm RECRYSTALLIZATION AS A WAY TO CONTROL THE NATURE OF GRAIN BOUNDARIES? 10o 20o 30o 40o 50o 60o 0% 30% ~30% of Σ3 boundaries (rotation 60o , axis <111>)
  23. 23. 23 “RAPID” HEAT TREATMENT: SPOT WELDING MACHINE 3mm 250 µm Fe annealed (thickness = 500 µm) Fe 60% cold rolled (thickness = 200 µm) Electrode of Cu Pulse discharge width: 1 msec Energy output: 100 J to 1 J Estimated heating rate ~105 K/sec Spot welding machine
  24. 24. 24 PHASE TRANSITION IN IRON 50 µm 50 µm 40 J 20 J Melted zone Heated zone  Refinement of the microstructure via phase transitions  Distribution in grain size from 40 µm down to less than 1 µm Spot welding machine
  25. 25. 25 RECRYSTALLIZATION AND PHASE TRANSITION IN IRON 40 J 50 µm100 µm  Refinement of the microstructure via phase transitions and recrystallization  Distribution in grain size from 100 µm down to less than 1 µm Spot welding machine Fe 60% cold rolled
  26. 26. 26 20 J 50 µm  Localized event along specific grain boundaries Spot welding machine RECRYSTALLIZATION AND PHASE TRANSITION IN IRON Fe 60% cold rolled
  27. 27. 27 Laser pulse:  Energy (nJ to µJ)  Time (fsec to nsec)  Beam size (µm to mm) Small volume on the surface  Rapid heating and cooling (104 to 1012 K/sec)  Increase in pressure (up to TPa) Shock wave. “ULTRA FAST” HEAT TREATMENT: PULSE LASER IRRADIATION (nano/pico/femtosecond) Cooperation with Preston/Haugen group ~100 nm to mm Pulse lasers
  28. 28. 28  λ = 800 nm  The beam has a Gaussian profile with a radius ω0  E0: full energy pulse (~10 µJ)  τp: duration of the pulse (~ 10 nsec/ 100psec/ 150 fsec)  φ: fluence or energy per unit area (J/cm2 )  φth: threshold fluence (J/cm2 ) fluence required to transform the surface Pulse lasers “ULTRA FAST” HEAT TREATMENT: PULSE LASER IRRADIATION (nano/pico/femtosecond)
  29. 29. 29 WHY PULSED LASERS? Pulse lasers
  30. 30. 30 SINGLE PULSE ABLATION OF FE E = 9.2 µJ 10 µm 5 µm E = 1.0 µJ 10 µm E = 3.2 µJ 5 µm E = 0.2 µJ  What is the temperature profile?  How to characterise the irradiated volume? Pulse lasers
  31. 31. 31 Si substrate SiO2 isolant layer Platinum 2 mm 2 mm 100 µm 25 nm2 µm resistor connector TEMPERATURE MEASUREMENT DEVICE Summer work of B. Iqbar Measuring the changes in resistivity of Pt estimating the temperature Pulse lasers
  32. 32. 32 Fe annealed, 1 grain Corrected harmonic contact stiffness: 1.106 N/m 0 10 20 30 200 400 600 800 1000 1200 Load On Sample (mN) Displacement Into Surface (nm) 1 2 3 4 5 [6] U HD I E M HN L 0 100 200 300 400 200 400 600 800 1000 1200 Reduced Modulus (GPa) Displacement Into Surface (nm) IM H N 0 2 4 6 8 10 12 14 16 0 200 400 600 800 1000 Hardness (GPa) Displacement Into Surface (nm) 1 2 3 4 5 [6] I M HN INSTRUMENTED INDENTATION Pulse lasers 0 10 20 30 40 200 400 600 800 1000 1200 Load On Sample (mN) Displacement Into Surface (nm) [2] 3 4 U HD I E M HN L Fe annealed, 3 different grains 0 100 200 300 400 200 400 600 800 1000 1200 Reduced Modulus (GPa) Displacement Into Surface (nm) I MH N 0 2 4 6 8 10 12 14 16 200 400 600 800 1000 1200 Hardness (GPa) Displacement Into Surface (nm) [2] 3 4 IM HN
  33. 33. 33 1 2 3 12 11 10 -1 0 1 2 3 4 5 6 7 100 200 300 400 Load On Sample (mN) Displacement Into Surface (nm) 1 2 3 4 5 6 7 8 [9] 10 11 12S U HDI EM H N L -2 0 2 4 6 8 10 12 14 16 18 20 100 200 300 400 Hardness (GPa) Displacement Into Surface (nm) 1 2 3 4 5 6 7 8 [9] 10 11 12 IM HN INSTRUMENTED INDENTATION Pulse lasers  Softening of the deformed material?  Is there local melting/solidification or local heating?
  34. 34. 34 SGGrain I Grain II nucleus Grain I Grain II )( 2 )( tr tG γ > Modeling ZUROB’S MODEL FOR RECRYSTALLIZATION  Needs input on local misorientations
  35. 35. 35 CONCLUSIONS – FUTURE WORK  Investigation of the first stage of recrystallization by: o Designing microstructures to promote N o Using rapid heat treatments to allow nucleation but not G o o  Characterize the heat treatment in terms of time/temperature profile  Characterize the “nucleation” event in terms of local misorientation, local strain gradient (EBSD)  Introduce the data on misorientation into Zurob’s model

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