recrystallization in metals - Course Notes - McMaster University

RECRYSTALLIZATION IN METALS
FLORENT LEFEVRE-SCHLICK and DAVID EMBURY
Department of Materials Science and Engineering
McMaster University, Hamilton, ON, Canada
1

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
2

Recrystallization
What is it
Fe
E =E stored
=~100J/mol
Deformation
Heat
Recrystallization
(development of new strain free grains)
Recovery
(rearrangement of dislocations in sub grains)
3

Recrystallization
HOW DOES RECRYSTALLIZATION START
“nucleation”
Coalescence and growth of subgrains
∆Θ 3
∆Θ 4
∆Θ 3
∆Θ 4
∆Θ 1
∆Θ 1
∆Θ 2
Strain Induced
Boundary Migration
Migration of a boundary
Θ 1
Θ 2
Θ 1
E 1 > E 2
Θ 2
Θ 2
In simple systems: small number of “nuclei” lead to recrystallized grains
4

Recrystallization
Improving the mechanical properties of materials
σY (MPa)
7000
6000
5000
4000
3000
2000
1000
Cu
Fe
Al
Grain refinement strengthening
0
0 2 4 6 8 10
d -1/2 (µm -1/2 )
How does recrystallization proceed
How to control recrystallization
How to achieve an important grain refinement
Can we control more than just the scale
5

Recrystallization
Johnson, Mehl, Avrami, Kolmogorov approach
recrystallized fraction X
X
1
0
n
= 1 − exp( −Bt
)
time
Random distribution of nucleation sites
Constant rate of nucleation and growth n=4
Site saturation n=3
6

Recrystallization
Johnson, Mehl, Avrami, Kolmogorov approach
Is n misleading
Site saturation 3d/2d/1d
3/2/1
Constant nucleation rate 3d/2d/1d
4/3/2
Fined grained Aluminium, low strain
4
Aluminium+ small amount of copper, 40% cold
rolled
Fe-Mn-C
1.7

Recrystallization
“NUCLEATION” OF RECRYSTALLIZATION
Large orientation gradient
(transition bands)
Strain heterogeneities
(shear bands)
Fe-Si system
Cu
Hu et al. (1966) Adcock et al. (1922)
8

Recrystallization
“NUCLEATION” OF RECRYSTALLIZATION
Particle Stimulated Nucleation
Oxide inclusions in Fe Al-Si system Cluster of SiO 2
in Ni
Leslie et al. (1963) Humphreys et al. (1977)
Recrystallization originates at pre-existing subgrains within the deformation zone
Nucleation is affected by particle size and particle distribution
9

Recrystallization
INVESTIGATING THE “NUCLEATION” EVENT
Injecting nucleation sites to increase N:
• Local misorientation (twins)
• Local strain gradient (high deformation)
Impeding growth of recrystallized grains
• Rapid heat treatments
o
10

Rapid heat treatments
What are rapid heat treatments
•“Slow” heat treatment
(salt bath)
•“Rapid” heat treatment
(spot welding machine)
•“Ultra-fast” heat treatment
(pulsed laser)
T
T
T
seconds
mseconds
time
time
nano/pico/femtoseconds
time
11

Salt bath
“Slow” heat treatment: Salt bath
Tim e/Tem perature profile during salt bath
heat treatm ent
700
Duration of the heat
treatment: 5 seconds.
Temperature range: 500 o C
to 650 o C.
Heating rate ~300C/sec
Cooling rate ~1000C/sec
Tem perature (C)
600
500
400
300
200
100
0
0 5 10 15
Time (sec)
12

Salt bath
“NUCLEATION” IN IRON
Fe deformed by impact at 77K
Production of deformation twins to promote a variety of potential
nucleation sites for recrystallization, either at twin/grain
boundary or twin/twin intersections
(1-11)
2-22
(-2-11)
-2-11
-200
21-1
01-1 -21-1
50 µm 4 µm B=[011]
Twinning plane {112}
Shear direction 111
grain
twin
13

Salt bath
“NUCLEATION” IN IRON
5 seconds at 500 o C
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).
0-11
ZA=[133]
-110
-310
-301
0-31
22-2 21-1
21-1
200
ZA=[011]
12-1 -301
ZA=[113]
-110
-110
BF images of a nuclei
along a deformed twin.
21-1
0-31
21-1
0-31
12-1
-301
12-1
-301
ZA=[113]
14
ZA=[113]

Salt bath
“NUCLEATION” IN COPPER
5 seconds at 250 o C
Cu 60% cold rolled
Cu ~ 2% recrystallized
50 µm
25 µm
1 µm 4 µm
No noticeable effect of annealing twins on nucleation
15

Salt bath
“NUCLEATION” IN STAINLESS STEEL
45% cold rolled @ 77K
Stainless steel 316L
100µm
Cooperation with X. Wang
16

Salt bath
“NUCLEATION” IN STAINLESS STEEL
Stainless steel 316L
2 min @ 950C
25µm
Average grain size: 7µm
17

Salt bath
“NUCLEATION” IN STAINLESS STEEL
2 min @ 900C
Stainless steel 316L
25µm
Average grain size: 5µm
18

Salt bath
“NUCLEATION” IN STAINLESS STEEL
Stainless steel 316L
2 min @ 850C
25µm
Average grain size: 3µm
19

Salt bath
“NUCLEATION” IN STAINLESS STEEL
Stainless steel 316L
1 min @ 800C
10µm
Role of annealing, deformation twins and phases on nucleation and growth
20

Salt bath
“NUCLEATION” IN STAINLESS STEEL
Stainless steel 316L
1 min @ 800C
BF image
DF image
(austenite + martensite)
DF image (austenite)
DF image (Twin)
Fine and complex deformed microstructure
Over a range of possible growing grains, only a few seem to grow
21

Salt bath
RECRYSTALLIZATION AS A WAY TO CONTROL THE NATURE
OF GRAIN BOUNDARIES
Stainless steel 316L, 2 min @ 850C
30%
25µm
0%
10 o 20 o 30 o 40 o 50 o 60 o
~30% of Σ 3
boundaries
(rotation 60 o , axis )
22

Spot welding machine
“RAPID” HEAT TREATMENT: SPOT WELDING MACHINE
Electrode of Cu
250 µm
3mm
Fe annealed (thickness = 500 µm)
Fe 60% cold rolled (thickness = 200 µm)
Pulse discharge width: 1 msec
Energy output: 100 J to 1 J
Estimated heating rate ~10 5 K/sec
23

Spot welding machine
PHASE TRANSITION IN IRON
Melted zone
40 J Heated zone 20 J
50 µm 50 µm
Refinement of the microstructure via phase transitions
Distribution in grain size from 40 µm down to less than 1 µm
24

Spot welding machine
RECRYSTALLIZATION AND PHASE TRANSITION IN IRON
Fe 60% cold rolled
40 J
100 µm
50 µm
Refinement of the microstructure via phase transitions and recrystallization
Distribution in grain size from 100 µm down to less than 1 µm
25

Spot welding machine
RECRYSTALLIZATION AND PHASE TRANSITION IN IRON
Fe 60% cold rolled
20 J
50 µm
Localized event along specific grain boundaries
26

Pulse lasers
“ULTRA FAST” HEAT TREATMENT: PULSE LASER IRRADIATION
(nano/pico/femtosecond)
Laser pulse:
Energy (nJ to µJ)
Time (fsec to nsec)
Beam size (µm to mm)
~100 nm
to mm
Small volume on the surface
Rapid heating and cooling
(10 4 to 10 12 K/sec)
Increase in pressure (up to TPa)
Shock wave.
Cooperation with Preston/Haugen group
27

Pulse lasers
“ULTRA FAST” HEAT TREATMENT: PULSE LASER IRRADIATION
(nano/pico/femtosecond)
λ = 800 nm
The beam has a Gaussian profile
with a radius ω 0
E 0
: full energy pulse (~10 µJ)
τ p
: duration of the pulse (~ 10 nsec/ 100psec/ 150 fsec)
φ: fluence or energy per unit area (J/cm 2 )
φ th
: threshold fluence (J/cm 2 )
fluence required to transform the surface
28

Pulse lasers
WHY PULSED LASERS
29

Pulse lasers
SINGLE PULSE ABLATION OF FE
E = 9.2 µJ
E = 3.2 µJ
10 µm
10 µm
E = 1.0 µJ
E = 0.2 µJ
5 µm
5 µm
What is the temperature profile
How to characterise the irradiated volume
30

Pulse lasers
TEMPERATURE MEASUREMENT DEVICE
2 mm
2 mm 100 µm
2 µm
Platinum
25 nm
SiO 2
isolant layer
resistor
connector
Si substrate
Measuring the changes in resistivity of Pt
Summer work of B. Iqbar
estimating the temperature
31

Pulse lasers
INSTRUMENTED INDENTATION
Fe annealed, 1 grain
Corrected harmonic contact stiffness: 1.10 6 N/m
Load On Sample (mN)
30
L U
Hardness (GPa)
16
Reduced Modulus (GPa)
400
14
12
300
20
10
10
8
6
1
2
3
4
5
[6]
200
1
2
M I
3 H
4N
5
[6]
4
2
HD E
0 M H I
0
N
200 400 600 800 1000 1200
Displacement Into Surface (nm)
Fe annealed, 3 different grains
M
N HI
0 200 400 600 800 1000
Displacement Into Surface (nm)
100
0
200 400 600 800 1000 1200
Displacement Into Surface (nm)
Load On Sample (mN)
Hardness (GPa)
Reduced Modulus (GPa)
40
16
400
14
30
L
U
12
300
20
10
8
6
[2]
3
4
200
I
M H
N[2]
3
4
10
4
100
0
EHD
MN
HI
200 400 600 800 1000 1200
Displacement Into Surface (nm)
2
0
M N H I
200 400 600 800 1000 1200
Displacement Into Surface (nm)
0
32
200 400 600 800 1000 1200
Displacement Into Surface (nm)

Pulse lasers
INSTRUMENTED INDENTATION
12 11 10
1 2 3
Load On Sample (mN)
7
Hardness (GPa)
20
6
5
4
3
2
1
0 S
-1
LU
MN
H I
EHD
100 200 300 400
1
2
3
4
5
6
7
8
[9]
10
11
12
18
16
14
12
10
8
6
4
2
0
-2
M N H I
100 200 300 400
Displacement Into Surface (nm)
1
2
3
4
5
6
7
8
[9]
10
11
12
Displacement Into Surface (nm)
Softening of the deformed material
Is there local melting/solidification or local heating
33

Modeling
ZUROB’S MODEL FOR RECRYSTALLIZATION
Grain II
Grain I
SG
Grain II
Grain I
nucleus
G(
t)
>
2γ
r(
t)
Needs input on local misorientations
34

CONCLUSIONS – FUTURE WORK
Investigation of the first stage of recrystallization by:
o Designing microstructures to promote N
o
o Using rapid heat treatments to allow nucleation but not G
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
o
35