This Presentation describes the advantages of using Accumulative Roll Bonding Process for Al 1100, and IF Steels for different cycles

1. Presented By :
INTRODUCTION TO ACCUMULATIVE
ROLL BONDING PROCESS (ARB).
Presented towards ME 631 Course Requirements
1
 PREM KUMAR VYDA
 TEJAS PATEL
 RUPESH PALWADI
 ENLIANG WANG
 RAVINDER RAVI
5/21/2018

2. PRESENTED BY :
NOVEL ULTRA-HIGH STRAINING PROCESS
FOR BULK
MATERIALS - DEVELOPMENT OF THE
ACCUMULATIVE
ROLL-BONDING (ARB) PROCESS.
Chapter 12
PREM KUMAR VYDA

3. Outline
3
 Introduction to ARB Process
 Design Application
 Experimental Procedure
 Results & Discussion
 Conclusion

4. Introduction to ARB Process
4
 It is Observed that Ultra-fine grain materials
exhibit desirable properties.
 High strength at ambient temperatures
 High-speed superplastic deformation at elevated
temperatures.
 High corrosion resistance.
 Commonly accomplished by intense plastic
straining for Industrial Applications.

5. Driving Forces for ARB
5
 Special Intense Plastic Straining Processes like Cyclic
Extrusion Compression (CEC) and Torsion Straining
(TS) have drawbacks.
• Requires Large Loads and Expensive Dies.
• Low Productivity, thus limiting economic viability.
• Inappropriate for Practical Applications.
 Accumulative Roll Bonding is a severe plastic
deformation process (SPD) introduced for bulk
material manufacturing and high productivity.

6. Design Application
 Principle
 Rolling bond surfaces
together
 Refines microstructure
 Improves properties.
 Iterative process
 Process design steps
 Surface treatment
 Stacking
 Roll bonding (heating)
 Cutting
6
Picture Credit : Acta Materialia Volume 47, Issue 2, 15 January
1999, Pages 579-583 Y. Saito

7. The ARB Process
7
1. Both the Strips to be Roll bonded are placed on top of each other after
surface treatment is performed.
2. The Two layers are then rolled , as in a conventional roll-bonding process
3. Now , the two layers are sectioned into two halves along the length.
4. The Sectioned Strips are again surface treated, stacked and roll bonded.
5. The process is repeated numerous times to achieve ultra-fine grain
structure.
6. The Process needs to be performed at elevated temperatures, but below
the recrystallization temperature, as recrystallization cancels out the
accumulated strain.
7. Low Temperatures would lead to insufficient ductility and bonding strength.
8. Treshold deformation decreases with temperature.
9. The process can introduce ultra-high plastic strain without any geometrical
change, if the reduction in thickness is maintained to 50% in every roll
pass.
10. Usually done without lubricant, so as to achieve good roll bonding.
Surface Treatment
Stacking
Heating
Roll Bonding
Cutting
Repeat‘n’times

8. 8
 For reduction of 50% in a pass
 Thickness after n cycles
 t = t0 / 2n
 Total reduction after n cycles
 rt = 1 – (t / t0 )= 1 – 1 / 2n
 Equivalent plastic strain assuming von-mises
condition

 Final Reduction for a Sheet of 1mm thickness
nn 80.0)}
2
1
ln(
3
2
{ 
Thickness Calculations after each
iteration.
Number of Cycles,(n) Final Thickness Achieved Total Reduction Achieved
7 7.8 µm 99.2%
10 1 µm 99.9%

9. Experimental Procedure
9
 Three alloys chosen
 Al 1100 (commercially pure)
 Al 5083 (Al-Mg alloy)
 Ti-added interstitial free (IF) steel
 Surfaces degreased, brushed
 Strips were heated
 50 % reduction rolling under dry conditions.
 Initial Dimensions of the materials are 1mm (thickness) X 20mm(width) X
300mm (length).
 The layered Strips were heated and roll-bonded with 50% reduction rolling
under dry conditions.

10. Experiment Parameters
10
Material Heating Mean Grain
Size (µm)
Roll Diameter
(mm)
Roll speed
(m/min)
Mean Strain
Rate (/s)
Al (1100) 473 K x 5 min 37 225 10 12
Al (5083) 473 K x 5 min 18 310 43 46
IF Steel 773 K x 5 min 27 310 43 46

11. Results
11
 Transmission electron microscopy (TEM) and
Tensile Test Studies were conducted.
 Optical Micrographs of ARB Processed IF
(Interstitial Free) Steel were recorded.
 Selected Area Diffraction(SAD) Patterns were
recorded for the three specimens.
 The Structure is made of Equiaxed grains.

12.  Interface in the first cycle is not clearer in quarter of the area.
Results Discussion (TEM Micrographs) – IF Steel12

13. • Interface more clear after 2 Rolling Cycles.
• After 5 cycles, elongated grains and uniform interfaces.
Results Discussion (TEM Micrographs) – IF Steel13

14. Selected Area Diffraction (SAD)
Patterns
 Structure is of granular type with
equiaxed grains. (grain size < 500
microns)
 These Patterns indicate large
misorientations between individual
grains.
14

15. Results
15
 Expected that grain refinement:
 Improves mechanical properties related to strength
 Decreased % elongation in direction of roll-bonding
 The number of cycles required to obtain peak
strength can only be determined experimentally.
 Deformation in the rolled sheets is strongly
affected by frictional condition between the rolls
and the metals

16. Results
16
Material # Cycles
Tensile Strength
(MPa)
% Elongation
Al (1100) 0 (Initial) 84 42
Al (1100) 8 304 8
Al-Mg (5083) 0 (Initial) 319 25
Al-Mg (5083) 7 551 6
IF Steel 0 (Initial) 274 57
IF Steel 5 751 6

17. Chapter 1 - Conclusion
17
 Practical industrial use for high strength
structural applications.
 Advances rolling technology by application to
a specific materials processing method.
 Industries most impacted: construction,
marine, aerospace, automotive

18. PRESENTED BY :
Role of shear strain in ultra grain refinement
by
accumulative roll-bonding (ARB) process.
Chapter - 218
PREM KUMAR VYDA

19. Introduction
19
 Evident that ARB is capable of producing ultra-fine grain structures with high
strengths in steel and Aluminum.
 Severe Plastic Deformation forms clear ultrafine grains with more equilibrium grain
boundaries.
 The detailed mechanism of grain subdivision and role of deformation conditions is
not yet established.
 During ARB Process, half of the surface regions move to the center during each
pass and the procedure is repeated.
 Complicated distribution of surface regions and higher strain introduced.
 Study tries to establish a relationship between shear strain distribution and ultragrain
refinement in ARB Processed Pure Aluminium (1100).

20. Experimental Procedure
20
 Aluminium alloy chosen
 Al (JIS-1100) (commercially pure)
 Initial Dimensions of the materials are 1mm (thickness) X 20mm(width) X 250mm
(length).
 50 % reduction per cycle under dry conditions. (No Lubrication Provided).
 8 Cycles were performed.
 Cylindrical Pin (Al 1100) 2mm (Dia) X 1mm (Height) was embedded.
 After the first cycle, the flection of the pin was observed with optical microscopy.

21. Fig. 1. Optical microstructures showing the flection of the embedded pin in the 1100
aluminum sheet ARB processed by one cycle at ambient temperature without lubricant.
Observed on a longitudinal section. (ND- Normal Direction , Rd – Rolling Direction)
Results21

22. Results Discussion22
 Shear Strains measured are plotted in dots.
 Curve Fitting is done on the plotted data.
 Plotted data follows parabolic distribution.
 4 cycle ARB Processed Al Sheet is filled with Pancake Shaped Ultra-Fine Grains with High-Angle Grain
Boundaries(>15º).
 Grain Thickness Varies depending on thickness location.

23. Chapter 2 - Conclusion
23
 The ARBed Aluminum Alloys with Ultra-fine
grains showed 3.7 times larger strength than the
corresponding starting material.
 ARBed Al-Mg Alloy with sub micrometer
(<1µm) grains showed low temperature super-
plasticity at 473K. (Half the melting
temperature of starting alloy).

24. PRESENTED BY :
Enhanced strength and ductility in Ultra-
Fine Grained (UFG) Aluminum produced by
ARB
Chapter 324
TEJAS PATEL

25. Material preparation
25
 The Aluminum sheets taken
for ARB are of 99.5 % purity
 The Dimensions of the
Sheets are 250 mm (length)
X 20 mm (width) X1 mm
(thickness)
 Heated at 580⁰ C
(recrystallization) for 1 hour

26. Experimental procedure
26
 50% of thickness reduction per roll pass.
 This process is repeated and number of
passes N are varied.
 The specimens are put under tensile test
using Instron 4505.
 The strain rate was varied from 1× 10⁻⁵
s⁻1 to 5× 10⁻ᶾ s⁻1.

27. Observations
 The grain size was determined
to be 540 nm in the rolling
direction and 320 nm in the
normal direction which falls in
the region of ultrafine grains.
27
Fig. 1 : TEM micrograph of UFG Al after 8 ARB cycles

28. Fig. 2 : Evolution of Vickers hardness and ultimate tensile strength (UTS)
with reference to number of ARB passes.28

29. Fig. 3 True stress vs true strain for UFG Al at different number of ARB
passes and for comparison cold-rolled Al with strain rate 1×10⁻⁴ s⁻129

30. Fig. 4 True stress vs true strain for UFG Al with 5 ARB passes tested at
different strain rate varying from 1×10⁻⁵ to 5×10⁻3 s⁻ 130

31. Take away points from the
experiment
31
 Increase in UTS by a factor of 3 compared to
recrystallized reference material.
 Increase in UTS by a factor of 1.8 compared to
cold rolled material.
 Increase in elongation to failure by a factor of 2
compared to cold rolled material.

32. PRESENTED BY :
Manufacturing process of aluminum foam
by accumulative roll bonding.
Chapter 432
TEJAS PATEL

33. Metal foams
33
 A metal foam is a cellular
structure consisting of a
solid metal with gas-filled
pores comprising a large
portion of the volume.
 The advantages of metal
foams over conventional
polymer include their high
melting point and high
toughness.
Fig. 1 : Metal foam

34.  Fig.2 : (a) Schematic illustration of
the manufacturing process of a sheet
through ARB process (b) : Prediction
of gradual distribution of added
blowing agent particles
34

35. Observations
35
Fig.3 : Optical (left) and SEM (right)
micrographs of the aluminum
preform sheet after (a) the first, (b)
third and (c) sixth cycles of ARB

36. Chapter 4 - Conclusion
36
 Using two Al 1050 aluminum strips and TiH2
powder as blowing agent, the preform aluminum
sheet was manufactured through six cycles of
the ARB process. Foaming tests were carried
out under various temperature profiles and the
effects of foaming conditions were revealed.
 Closed-cell aluminum foams with about 40%
porosity were successfully produced through the
ARB process.

37. PRESENTED BY :
Accumulative Roll Bonding of Interstitial-
Free (IF) Steel
Chapter 537
TEJAS PATEL

38. Introduction
38
 Basic ARB process discussed in previous slides.
 The Influence of ARB on the Mechanical
Properties of IF Steel are studied, as steel is the
most useful structural element.
 Studied at 773 K temperature with 50% reduction
in each roll pass.
 Degree of bonding and grain size achieved
depend on the number of rolling passes.

39. Experimental Procedure
39
 Same as ARB Process mentioned in the previous
slides.
 Blue Brittleness of Steel during rolling at warm
temperatures can be avoided due to scarce
presence of carbon atoms.
 Fully annealed IF Steel Sheets with
1mm(thickness), 20mm(width) and 300mm
(length) were provided for ARB process.

40. Experimental Procedure – contd.
40
 7 ARB cycles were carried out for the
specimen.
 Tensile tests at ambient temperature were
carried out using an instron-type machine.

41. • Tensile strength increased with increasing strain. Reached 870 Mpa from 280
MPa after 7 cycles.
Fig 1. Mechanical properties at ambient temperature of the IF
steel after various cycles of ARB at 773 K.41

42. Figure 2. TEM microstructures and corresponding SAD patterns of the IF steel after
various cycles of ARB at 773 K. (a) After 1 cycle (50% reduction, true strain of 0.8).
(b) 3 cycles (87.5% reduction, true strain of 2.4). (c) 6 cycles (98.4% reduction, true
strain of 4.8). (d) 7 cycles (99.2% reduction, true strain of 5.6).
SAD Patterns and TEM Microstructures42

43. Conclusions
43
 In addition to aluminum alloys, ultra-fine grained
bulk steel (interstitial free (IF) steel) whose mean
grain size is less than 1 micron was successfully
produced by Accumulative Roll-Bonding (ARB)
process.
 The ultra-fine grained IF-steel with mean grain
size of 420 nm showed very large tensile strength
of 870 MPa.
 3.1 times larger than that of the starting material.

44. PRESENTED BY :
Effective parameters and microstructure
homogeneity in ARB
Chapter 644
RUPESH PALWADI

45. CONTENTS
45
 Bond length parameter
 Peeling test
 Parameters influencing roll bonding
 Microstructure homogeneity

46. Bond length
46
 Length from *bonding point to the exit point.
 Relative bond length (l/L)
l – bonding length
L – Horizontal projection of roll-contact
strip length.
*point after which the layers deform with a constant thickness ratio (t1(x)/t2(x)).

47. Deformation zone
47

48. Peeling Test
48
 Materials
 Al 1050, Al 1100
 St12, St37 ( low carbon steels )
 aluminum 1050/steel/aluminum 1050, aluminum 1050/aluminum
1100/aluminum 1050 strips are used.

49. Peeling Test
 Average peel strength
was calculated by dividing
average load by bond
width.
 Tests were carried out at
a crosshead speed of
20 mm/min.
49

50. Peeling Test
Mean contact
pressure P = F/WL
 F = Rolling Force
 W = Width of bond
strip
 L =Length of bond
strip
50

51. Peeling Test
 m1 = fstrip and rolls
 m2 = fclad layer and base
metal
 tst = Thickness of steel
sheet
 tal = Thickness of
Aluminium sheet
 W = Width of the sheet
 Ro = Radius of the roll
51

52. Parameters influencing roll bonding
52
 Composite reduction
 Rolling speed
 Internal layer thickness
 Internal layer yield strength

53. Composite reduction
53
Relative bond length and average
peel strength increases with increase
in composite reduction.
 Increase in total composite
reduction moves the created inter-
layer bonding point towards the roll
entrance . This shift can be
interpreted in terms of the critical
deformation required for a cold bond
establishment.
 Therefore, it can be stated that the
creation of inter-layer bonding point
originates from existence of the
critical strain [39]

54. Rolling speed
54
It shows that increasing of rolling speed causes
a bit higher amounts of mean contact pressure on
interfaces.
 the reason for the small variations of the
mean contact pressure versus total
reduction in different rolling speeds is that
the coefficient of the strain rate sensitivity
for the most of the metals is very small
at ambient temperatures.
 The promotion of the rolling speed
decreases the exertion time of the
mean contact pressure on
inter-layer interfaces.

55. Rolling speed
 In a constant total
reduction,
the mean bond strength
decreases with increasing the
rolling speed. Moreover,
threshold
 Deformation is increased
from
11% for rolling speed of
42.5rpm to
12% for 65.5rpm and
13.5% for 92.5 rpm. 55

56. Internal layer thickness
56
 In a constant total reduction, mean
contact pressure increased with
decreasing the thickness of internal
steel layer despite the falling of rolling
force . This is attributed
to decrease in strip-roll contact length
dominates the effect of decrease in
rolling force and results in increasing
of mean contact pressure.
 Two thicknesses of 1 and 1.5mm were
Applied to St12 internal layer. As it can be
seen, in a constant total reduction,
decreasing the Internal layer thickness
caused the increasing of relative bonding
length.

57. Internal layer thickness
 Threshold deformation for
l1050/St12/Al1050 tri-layer strip
decreases from 11% for samples
with internal layer thickness of
1.5mm to 10% for those with
1mm
internal layer thickness.
57

58. Internal layer yield strength
 Al1050/Al1100/Al1050,
Al1050/St37/Al1050 and
Al1050/St12/Al1050 in a
constant thickness
reduction, the internal
layer with higher yield
strength increases the
Mean contact pressure on
layers’ interface.
58

59.  It shows that
decreasing of the yield
strength
of the internal layer in a
constant composite
reduction and the same
external layer led to
an increased relative
bonding length.
59

60. Internal layer yield strength
 It decreases the
threshold deformation
from14.5% for
internal layer of St37
to
10% for internal layer
of St12 and 9% for
Al1100.
60

61. Microstructure homogeneity
 SPD of 4.8 strain through
ARB
 Materials: Commercial
purity aluminum (AA1100),
oxide free high conductivity
(OFHC) copper, 36% Ni
austenitic steel and ultra
low-carbon interstitial free
(IF) steel (ferritic steel).
 Field-emission type
scanning electron
microscope (FE-SEM/EBSP)
pattern analysis
61

62. Microstructure homogeneity
62

63. Microstructure homogeneity
63

64. Microstructure homogeneity
64
dl = Length of elongated UFGs , dt = Thickness of elongated UFGs
Micro structure at subsurface more equiaxed compared to quarter thickness
and centre.

65. Microstructure homogeneity
65

66. Microstructure homogeneity
66
79% 54%
74% 87%

67. Microstructure homogeneity
67

68. PRESENTED BY :
Two composites produced by roll bonding
Chapter 768
ENLIANG WANG

69. ●Composite materials
●ARB vs RRB process
●Test result of Al/Ti
●Test result of AlSiC
Contents

70. Composite material
● made from two or more constituent materials with significantly different
physical or chemical properties
● when combined, produce a material with characteristics different from the
individual components
Composite
Particle-reinforced Fibre-reinforced Structural
MMC: Al/Ti , AlSiC

71. Al/Ti Composite
Titanium
10mm
25mm
Aluminum
Al/Ti composite:
Low density
Less expensive
High tensile strength
(20 Vol.% Ti)

72. AlSiC Composite
SiC
250+ crystal forms
Abrasive, Ceramic ,Wafer
10mm
Aluminum
AlSiC composite:
Low density
High thermal conductivity
Adjustable thermal expansion
AlSiC-9 (66 Vol. % SiC)
AlSiC-10 (55 Vol.% SiC)
AlSiC-12 (37 Vol.% SiC)
(5 Vol.% SiC)

73. Fabrication process ARB vs RRB
+AnnealingRRB:
AlSiC RRB:
Al strip: Al alloy 1050, 200x30x0.5mm
SiC particle: 5um, 5 Vol.%
Annealing: 623K for 1 hour
66% reduction at 1st and 2nd rolling
50% reduction of the last 6 rollings
Al Ti ARB:
Al foil: thickness 250 um
Ti foil: thickness 50 um
Total stack: 4mm,
50% reduction per 1 rolling
Strain rate: 30s−1

74. SEM images after different ARB cycles
a) Layers are uniform and coherent
b) non-uniform and shear bands
c,d, e) Fragmented Ti layers, multiple necking,
shear bands
f) Dispersed mixture of Ti and Al, uniformly
distributed
Ti/Al : Microstructure

75. TEM images within Al layers after different ARB cycles
a) homogeneous lamellar structure
b,c) Both equiaxed grains and Lamellar structure
d) almost filled with equiaxed grains
Ti/Al : Microstructure

76. TEM images of Ti after different ARB cycles
a ) Most of the layers contained lamellar structure elongated parallel
to the RD
b,c) Both equiaxed grains and Lamellar structure
d) almost filled with equiaxed grains
Ti/Al : Microstructure

77. Ti/Al : Stress-Strain Curves
Stress-Strain curves for different ARB
cycles
1) Significant increase in the yield stress
and ultimate tensile strength
2) Elongations decreased rapidly

78. Variation of microhardness after different ARB
cycles
1) As cycles increase, both hardness tend to
increase
2) both Curves converged
Ti/Al : Microhardness

79. Ti/Al : Strength comparison
Strength from testing vs strength from
mixture rule
1) Fit well after 5 cycles and reach peak at 12
cycles
2) Variation between 3 and 5, due to shear
bands

80. 1)Significant increase in the yield and tensile stress
1)Strain-hardening effects led to: Multiple necking, homogeneous distribution
1)Critical factors: large applied shear strain, high strain rate, reversing rolling
direction, low thermal conductivity
Ti/Al : Summary

81. 1) SiC particles decreased the peeling force
2) More than 60% deformation is needed to create acceptable bond
With SiC
40%
50%
60%
70%
73%
Without SiC
30%
40%
50%
60%
66
%
Al/SiC : Peel Test

82. 1st Cycle 2nd Cycle 5th Cycle 7th Cycle
Optical micrographs in various cycles.
1) Layer structure to composite
1) Concentrated SiC to uniform distributed Sic
Al/SiC : Microstructure

83. 1st Cycle 3rd Cycle 4th Cycle 7th Cycle
SEM micrographs after various cycles
1) SiC clusters were broken
1) Porosities were closed
1) Uniform distribution of SiC
Al/SiC : Microstructure

84. Stress-Strain Curves in various cycles
Tensile strength increased by increasing the RRB
cycle
1) Bonding strength increased
1) Porosities omitted
1) SiC dispersed more uniformly
Al/SiC : Stress-Strain Curves

85. Critical factors influencing the mechanical properties:
1) SiC particles 2) number of rolling cycles
Al/SiC : Strength comparison
Stress-Strain curve comparison
(7 cycles RRB & NO RRB)
Tensile strength comparison

86. Al/SiC : Summary
1) Bonding strength increased by increasing the plastic deformation
1) Porosities omitted and SiC particles uniformly distributed after 7 RRB
cycles
1) Tensile strength reached maximum value of 123Mpa after 7 cycles

87. PRESENTED BY :
Microstructure evolution and nano grain
formation during shear localization of
Titanium.
Chapter 887
Ravinder Ravi

88. Contents
88
 Introduction
 Experimental procedures
 SEM investigations of the shear localization at different rolling reductions
 TEM quantification of the microstructure refinement within shear bands at different rolling reductions
 TEM study of the microstructure refinement within shear bands at different rolling reductions
 Conclusion

89. Introduction
89
 Highly localised deformation develops in a majority of metallic materials.
 The shear bands experience high strain and stress rate and the shear localisation is considered
adiabatic.
 Several detailed investigations were conducted using the combination of various techniques like
electron backscattering diffraction, scanning electron microscopy (SEM) and transmission electron
microscopy (TEM) which described the evolution of well-recovered microstructures within shear
bands which were formed during rolling.
 Apart from dislocation slip processes, mechanical twinning plays an important role.
 The activation of deformation twinning results in progressive grain refinement owing to the
intersection of twins and the formation of secondary and tertiary twins.

90. Experimental Procedures:
90
 A commercial titanium plate with a fully recrystallized microstructure and a mean grain size of 60
µm was used. It was rolled at a strain rate of 3s-1 from 12 to 2 mm in thickness with a reduction of
16.7% per pass.
 The von Mises equivalent strains corresponding to different rolling reductions were calculated.
 The microstructures both from outside and within the shear localization areas were investigated
using TEM and SEM techniques. The observation sections were perpendicular to the transverse
direction(TD) of the rolled plate.
 While performing the TEM investigation thin foils were prepared, in which firstly a slice of the
rolled specimen was cut perpendicular to the TD and one side of the slice was metallographically
polished and etched to reveal the shear band location marking the location with a light scratch .
 Slice was grinded from the opposite side to a sheet of 100µm thick. A disc 3mm diameter punched
out ensuring the rolling direction was marked on the disc rim and then the disc was grounded to
50µm in thickness and finally subjected to low-energy ion milling to perforation.

91. SEM investigations of the shear localization at different
rolling reductions
91
Fig1: SEM micrographs of shear
bands developed at different
rolling reductions: a) 33% b) 50%
c) 67% and d) 83%. *ND- Normal
direction and RD- Rolling
direction.

92. Fig 2: Deformation twinning within deformed grains at
33% rolling reduction
S- like
appearance
Deformation twinning
92
 Micro-regions with localized shear were first initiated close to the edge of the rolled plate at a rolling reduction of 33% (Fig 1a). The
flow lines in these micro-regions were extensively stretched and curved in S-like appearance. Deformation twinning frequently occurred
within the surrounding elongated grains, as shown in Fig. 2.

93. TEM quantification of the microstructure refinement within
shear bands at different rolling reductions.
93
 Microstructures
obtained after 33%
rolling reduction
contained sheared
micro grains which
were significant from
other surrounding
matrix (Fig 3a).
 Fig 3: TEM micrographs
obtained after 33%
rolling reduction
 Bright field image of a
sheared micro grain
marked B and the matrix.
Inset showing Selected
area diffraction (SAD)
and RD indicates rolling
direction
 High-magnification
bright field.
At 33% rolling reduction

94. At 50% rolling reduction
94
 Fig 4: TEM micrographs
obtained after 50%
rolling reduction. (a)
Bright field image of
region containing
localized microscopic
shear band delineated by
the dashed lines. (b) Dark
field image of shear
band. (c) sub grain size
distribution for
microscopic shear band
(inset shows dl / dt ratio).
(d) Distribution of angles
between sub grain axis
and RD.
 After 50 % rolling
reduction, a localized
shear band clearly
distinguished from the
surrounding matrix.

95. At 67% rolling reduction
95
 Fig 5: TEM
micrographs obtained
after 67% rolling
reductions. (a) Bright
field image of region
containing localized
microscopic shear band
delineated by the
dashed lines. (b) Dark
field image of shear
band. (d) sub grain size
distribution for
microscopic shear band
(inset shows dl / dt
ratios). (d) Distribution
of angles between sub
grain elongation axis
and RD.

96. At 83% rolling reduction
96
Fig 6: TEM micrographs
obtained after 67%
rolling reductions. (a)
Bright field image of
region containing
localized microscopic
shear band delineated by
the dashed lines. (b)
Dark field image of nano
sized sub grains present
in the shear band market
in the centre in a. (d) sub
grain size distribution for
microscopic shear band
(inset shows dl / dt
ratios). (d) Distribution
of angles between sub
grain elongation axis and
RD.

97. TEM study of the microstructure refinement within
shear bands at different rolling reductions.
97
 Fig 7: TEM analysis of
mechanical twin formed in
the area separating a sheared
micro grain and the matrix at
33% rolling reduction.(a)
Bright field image of twins
composing T1 , T2 and T3
embedded in matrix M. (b),
(c), (d), (e), (f) SAD patterns
obtained from M T1 , T2 and
T3 respectively.
 ** ( Zhu et al., Stanford N,
Carlson U, Barnett MR.
Metall Mater Trans
A2008;39A:934. )
 Looking at fig 7 we can see
that three segments T1 , T2
and T3 were present in the
twin lamellae.

98. Fig 8: (a) TEM bright-field micrograph of the thin lath structure formed after 83% rolling
reduction (b) Schematic representation of the lamella longitudinal process enhanced by
shear bulging of its boundary. ** (Xue Q, Gray III GT. Metall Mater Trans A
2006;37:2447
98
Fig 8a reveals an array of
parallel elongated laths
largely separated by
high-angle boundaries,
presumably originating
from the matrix/twin
lamellae, containing
some low-angle
longitudinal dislocation
walls in the process of
formation at 83% rolling
reduction (marked by
arrows).

99. TEM bright field-image of long laths breaking down into sub grains through formation of
transverse dislocation boundaries after 67% rolling reduction in a localized microscopic
shear band. (b) Dark field image (c) Gradual transverse breakdown process
99
TEM bright
field-image
• Bamboo node
dislocations
TEM bright
field-image
• Large angle
boundaries separating
elongated sub grains
with increasing shear
strain

100. Fig 10: TEM bright field image of thin lath structure at boundary of localized
microscopic shear band after 67% rolling reduction containing area 2
connected to the parent lath 1.
100
TEM
observations in
fig 10 reveal the
progressive
change of
elongated lath
segments into fine
elliptical, facetted
sub grains which
are found in the
interior of the
microscopic shear
band and in the
exterior as well.

101. Schematic representation of the suggested mechanism of the microstructure evolution within the shear band
interior with increasing strain: (a) Formation of the mechanical twin/matrix lamellae. (b) Longitudinal splitting
of the lamellae to form thin laths. (c) Transverse breakdown of the laths to form elongated sub grains. (d)
Further breakdown and rotation of the sub grains to form equiaxed nano scale (sub)grains. The grey level is
proportional to the local shear strain.
101
Twin Lamellae Thin Lath
structure
Elongated sub
grains
Roughly equiaxed
nano sized sub
grains

102. Conclusion
102
 Sheared micro-regions are first initiated at low strains, and further shear localization with increasing strain leads
to the formation of distinct microscopic shear bands, inclined to the RD at 40º, containing a mix of thin lath
structures and elongated sub grains.
 The microscopic shear bands gradually grow and finally merge to form a macroscopic shear band containing thin
lath structures in the boundary regions, fine elongated sub grains in the outer areas and roughly
equiaxed(sub)grains with a mean size of 70 nm in the centre region.
 The early stage of shear localization involves the formation and multiplication of mechanical twins, giving rise to
the twin/matrix lamellar structure aligned along the shear direction.
 The twin/matrix lamellae subsequently undergo gradual splitting into thin laths through the formation of
longitudinal dislocation walls as well as progressive transverse breakdown via the formation of transverse
dislocation boundaries, which gives rise to the fine elongated sub grains.
 The continuing thermally assisted lath breakdown, in conjunction with lateral sliding and lattice rotations,
ultimately leads to the formation of a mix of roughly equiaxed, nano sized (sub)grains and grains in the
macroscopic shear band centre at large strains.
 The gradual microstructure fragmentation process within the shear localization areas might be described within
the Risø framework of deformation microstructure evolution by slip pr

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105. References
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106. Questions???
106