Jeffrey Rogers Seldenrust, B. S. , Texas A&M University. Co-Chairs of Advisory Committee: Dr. R. E. Goforth. Dr. M. N. Srinivasan. Weldalite 049 is a dynamically ...
SUPERPLASTIC AND MICROSTRUCTURAL CHARACTERIZATION
OF WELDALITE 049
A Thesis
by
JEFFREY ROGERS SELDENRUST
Submitted to the Office
of Graduate Studies of
Texas A&M University in partial fulfillment
of the
requirements
for the degree of
MASTER OF SCIENCE
December 1991
Major Subject: Mechanical Engineering
SUPERPLASTIC AND MICROSTRUCTURAL CHARACTERIZATION
OF WELDALITE 049
A Thesis by
JEFFREY ROGERS SELDENRUST
Approved
as to style and content by:
Ramon (Co-Chairman
E.
Malur N. Srinivasan (Co-Chairman of Committee)
forth
of Committee)
Walter L. Bradley (Head of Department)
Do
d lak (Member)
December 1991
ABSTRACT
and Microstructural
Superplastic
Characterization
of Weldalite 049. (December 1991)
B.S., Texas A&M
Jeffrey Rogers Seldenrust,
Weldalite 049 is a dynamically
is produced
by thermomechanical
alloy was investigated
aluminum
of 400 psi. The
Instability
localized necking.
optical
The superplastic
of the
behavior
using constant true strain rate tests at a back pressure
specimens were elongated to failure varying both the strain rate and
the temperature.
conditions.
pseudo single phase alloy that
recrystallizing
processing.
University
Dr. R.E. Goforth Dr. M. N. Srinivasan
Co-Chairs of Advisory Committee:
Microstructural
microscopy,
analysis
The activation
was conducted
energy
characterization
scanning
electron
to determine
was determined
the effect
of the
for the various testing
was conducted on all the samples using
microscopy,
and
transmission
electron
microscopy. The results indicate that the highest elongation is obtained when the sample is
tested at the slowest
strain rate,
0.0002 (sec'), at a
activation energy values are significantly
temperature
lower than that for pure lattice diffusion or
pure grain boundary diffusion, indicating that other mechanisms recrystallization
of 490'C. The
also contribute to the superplasticity
such as recovery and
of Weldalite 049.
DEDICATION
To my parents, John and Jan Seldenrust, and my fiancee, Denise Deleery, for their support,
guidance,
ARM University.
and encouragement
through
my graduate
studies at Texas
ACKNOWLEDGEMENTS
I want to
thank
my co-chairs,
Dr. Goforth and Dr. Srinivasan,
support and guidance through my graduate program.
gratitude to Dr. Saylak for his time and support.
for their
I would also like to extend
my
V1
TABLE OF CONTENTS Page
ABSTRACT DEDICATION
1V
ACKNOWLEDGEMENTS
TABLE OF CONTENTS
V1
LIST OF FIGURES . .
1X
LIST OF TABLES
XV
NOMENCLATURE
XV1
1.
INTRODUCTION
1.1
Background
1.2 Mechanics of Superplasticity
1.3
Types of Superplasticity
1.4 Processing Dynamically Recrystallizing Pseudo Single Phase Alloys 3
for Superplastic Characteristics
1.5 Prerequisites for Microstructural
Superplasticity
of Superplastic Behavior .
1.6 Characterization Deformation
1.7
Proposed Models for Rate Controlling in Superplasticity .
Mechanisms
1.7. 1 Diffusional Accommodation 1.7.2 Dislocation Accommodation
within Grains
1.7. 3 Dislocation Pile-Up Accommodation the Interfaces
in
10
vn
Page
2. EXPERIMENTAL PROCEDURE 2. 1
AND ANALYSIS
.
13
Alloy Composition and Sample Processing Details
13
2.2 Test Matrix for Weldalite 049
14
2. 3 Mechanical Testing
15
2.4 Instability
19
2. 5 Activation Energy
23
2.6 Microstructural
Evaluation
2.6. 1 Optical Microscopy .
3.
.
25
. . 25
2. 6.2 Scanning Electron Microscopy
. 27
2. 6.3 Transmission
. 27
Electron Microscopy
TEST RESULTS AND DISCUSSION .
28
3. 1 Mechanical Testing
28
3.2
Instability
Analysis
3.2. 1 Temperature=470'C 3.2. 2 Temperature =490'C
36
3.2. 3 Temperature =510'C
. . 42
3.2.4 Temperature=530'C
3.3
Activation Energy Analysis
53
3.3. 1 Strain Rate=0. 0002 (sec ')
. . 53
3, 3.2 Strain Rate=0. 0004 (sec ')
57
3.3.3 Strain Rate=0. 0006 (sec ')
Page
3.3.4
Strain Rate=0. 0008 (sec ')
3.3.5
Summary
3.4
Optical Microscopy
3.5
Scanning Electron Microscopy
69
70
.
.
74
3.6 Transmission Electron Microscopy
77
4. CONCLUSIONS
82
REFERENCES
84
APPENDIX
I.
TEST MATRIX RESULTS
II. STRAIN RATE SENSITIVITY VALUES III. ACTIVATION ENERGY VALUES VITA
86
98 102 104
LIST OF FIGURES Page
Figure
1.
Schematic of Processing Dynamically
2.
Schematic of Log(stress) versus Log(strain-rate)
3.
Ashby and Verrall Model
4.
Grain Switching
5.
Ball and Hutchison Model
6.
Mukherjee
7.
Schematic of Test Sample
13
8.
Testing a Superplastic Specimen on the Instron 1137
16
9.
Schematic of Experimental
17
10.
Closeup View of Retort
11.
Typical Stress vs Strain Diagram
19
12.
Instability
23
Recrystallizing
Alloys
Diagram
12
Model
Setup
18
Analysis
13.
Graph
14.
Test Specimen Displaying
Directions
15.
Test Specimen Displaying
Location of Microstructural
16.
Stress vs Strain Curves, Temperature=470'C
of ln(stress)
.
vs 1/temp
. 24 26
Samples
26
30
17a. Stress vs Strain Rate, Temperature=470'C Strain =0. 1-0.7 (in/in)
. . 31
17b. Stress vs Strain Rate, Temperature=470'C Strain =0.8-1.4 (in/in)
. 31
17c. Stress vs Strain Rate, Temperature=470'C Strain=1. 5-1.8 (in/in)
. . 32
Page
Figure
18.
Strain Rate Sensitivity vs Strain, Temperature=470
. . 33
C
19.
Strain Hardening
Coefficient vs Strain, Temperature=470'C
35
20,
Instability Parameter vs Strain Curves, Temperature=470'C
35
21.
Stress vs Strain Curves, Temperature=490'C
22a.
Stress vs Strain Rate, Temperature=490'C
22b.
22c.
. 37
Strain=0. 1-0.7 (in/in)
38
Stress vs Strain Rate, Temperature=490'C Strain =0.8-1.4 (in/in)
38
Stress vs Strain Rate, Temperature=490'C Strain =1.5-1.7 (in/in)
39
23.
Strain Rate Sensitivity vs Strain, Temperature=490'C.
24.
Strain Hardening
25.
Instability
26.
Stress vs Strain Curves, Temperature=510'C
27a.
Stress vs Strain Rate, Temperature=510'C Strain =0. 1-0.7 (in/in)
27b.
Stress vs Strain Rate, Temperature=510 Strain=0. 8-1.4 (in/in)
...
. . 39
Coefficient vs Strain, Temperature=490'C
41
Parameter vs Strain Curves, Temperature=490'C
41
..
43
43 C
44
27c. Stress vs Strain Rate, Temperature=510'C Strain =1.5-1.9 (in/in)
44
28.
Strain Rate Sensitivity vs Strain, Temperature=510'C
46
29.
Strain Hardening
30.
Instability
31.
Stress vs Strain Curves, Temperature=530'C
Coefficient vs Strain, Temperature=510'C
Parameter vs Strain Curves, Temperature=510
C
46
47
. . 49
Page
Figure
32a.
Stress vs Strain Rate, Temperature=530'C Strain =0. 1-0.7 (in/in)
49
32b.
Stress vs Strain Rate, Temperature=530'C Strain =0.8-1.4 (in/in)
50
32c. Stress vs Strain Rate, Temperature=530 C Strain =1.5-1.7 (in/in)
50
33.
Strain Rate Sensitivity vs Strain, Temperature=530
34.
Strain Hardening
35.
Instability
36.
Stress vs Strain Curves, Strain Rate=0. 0002 (sec ')
37.
Ln(stress) vs 1/Temp. Curves, Strain
38.
Activation Energy vs Strain Curves, Strain
.
. . .
. . . 52
Parameter vs Strain Curves, Temperature=530'C
52 54
Rate=0. 0002 (sec ') Rate=0. 0002
55
(sec'). . . . .
Range, Strain Rate=0. 0002 (sec ')
39.
Activation Energy vs Temperature
40.
Stress vs Strain Curves, Strain Rate=0. 0004 (sec
41.
Ln(stress) vs 1/Temp. Curves, Strain
42.
Activation Energy vs Strain Curves, Strain
43.
Activation Energy vs Temperature
44.
Stress vs Strain Curves, Strain Rate=0. 0006 (sec
45a.
. . 51
C
Coefficient vs Strain, Temperature=530'C.
Rate=0. 0004 (sec ')
Range, Strain
Ln(stress) vs 1/Temp. Curves, Strain
. . 56 . . 58
')
Rate=0. 0004 (sec
. 56
58
'). . . . . . 59
Rate=0. 0004 (sec ') . . 59 ')
Rate=0. 0006 (sec')
Strain=0. 1-0.7 (in/in)
. 61
Rate=0. 0006 (sec ')
45b.
Ln(stress) vs 1/Temp. Curves, Strain Strain =0.8-1.4 (in/in)
46a.
Activation Energy vs Strain Curves, Strain Strain =0. 1-0.7 (in/in)
. 61
Rate=0. 0006 (sec ')
. 62
Figure
Page
46b
Activation Energy vs Strain Curves, Strain Rate=0. 0006 (sec ') Strain=0. 8-1.4 (in/in)
47a
Activation Energy vs Temperature Strain = 0. 1-0.7 (in/in)
Range, Strain
Activation Energy vs Temperature
Range, Strain Rate=0. 0006 (sec ')
62
Rate=0. 0006 (sec ') 63
Strain=0. 8-1.4 (in/in)
63
48.
Stress vs Strain Curves, Strain Rate=0. 0008 (sec ')
49a
Ln(stress) vs 1/Temp. Curves, Strain Rate=0. 0008 (sec ') Strain
49b
=0. 1-0.6 (in/in)
.
. 65
.
. 66
Ln(stress) vs 1/Temp. Curves, Strain Rate=0. 0008 (sec ') Strain
=0.7-1.3 (in/in)
66
Rate=0. 0008 (sec ')
Soa
Activation Energy vs Strain Curves, Strain Strain =0. 1-0.7 (in/in)
50b
Activation Energy vs Strain Curves, Strain Rate=0. 0008 (sec ') Strain =0.8-1.3 (in/in)
sla
Activation
Energy vs Temperature Strain=0. 1-0.6 (in/in)
67
.
. 67
Range, Strain Rate=0. 0008 (sec ')
51b. Activation Energy vs Temperature Range, Strain Rate=0. 0008 (sec ') Strain=0. 7-1.3 (in/in) . . . . . . . . . . . . . . . . . 68
52.
Grain Size vs Testing Time Plot for
G'"'
73
53.
Grain Size vs Testing Time Plot for
B'"'
. . 73
54.
Scanning Electron Photomicrograph, 200X Strain Rate=0. 0002 (sec ') Temperature=470
55.
Scanning Electron Photomicrograph, 200X Strain Rate=0. 0002 (sec ') Temperature=490'C
75
56.
Scanning Electron Photomicrograph, 200X Strain Rate=0. 0002 (sec ') Temperature=510'C
76
C
75
xut
Figure
Page
57
Scanning Electron Photomicrograph, 200X Strain Rate=0. 0002 (sec ') Temperature=530
58
Transmission Electron Photomicrograph, 90,000X Strain Rate=0. 0002 (sec ') Temperature=510'C
..
59
Transmission Electron Photomicrograph, 90,000X Strain Rate=0. 0004 (sec ') Temperature=490'C
. . 79
Transmission Electron Photomicrograph, 90, 000X Strain Rate=0. 0006 (sec ') Temperature=490'C .
80
61
Transmission Electron Photomicrograph, 90, 000X Strain Rate=0. 0008 (sec ') Temperature=490'C
81
62.
Stress vs Strain Curves, Strain Rate=0. 0002 (sec') Temperature =470'C
. . 86
63.
Stress vs Strain Curves, Strain Rate=0. 0002 (sec ') Temperature =490'C
86
Stress vs Strain Curves, Strain Rate=0. 0002 (sec ') Temperature
=510'C
87
65.
Stress vs Strain Curves, Strain Rate=0. 0002 (sec ') Temperature =530'C
87
66.
Stress vs Strain Curves, Strain Rate=0. 0004 (sec ') Temperature =470'C
88
67.
Stress vs Strain Curves, Strain Rate=0. 0004 (sec ') Temperature =490'C
C
76
..
78
88
68.
Stress vs Strain Curves, Strain Rate=0. 0004 (sec ') Temperature =510'C
89
69.
Stress vs Strain Curves, Strain Rate=0. 0004 (sec ') Temperature
=530 C
89
70.
Stress vs Strain Curves, Strain Rate=0. 0006 (sec ') Temperature =470'C
. . 90
xjv
Page
Figure
71.
Stress vs Strain Curves, Strain Rate=0. 0006 (sec ') Temperature=490'C
. . 90
72.
Stress vs Strain Curves, Strain Rate =0.0006 (sec') Temperature
. . 91
73.
Stress vs Strain Curves, Strain Rate=0. 0006 (sec ') Temperature=530'C
. . 91
Stress vs Strain Curves, Strain Rate=0. 0008 (sec ') Temperature=470'C
..
92
75.
Stress vs Strain Curves, Strain Rate=0. 0008 (sec ') Temperature=490'C
..
92
76.
Stress vs Strain Curves, Strain Rate=0. 0008 (sec ') Temperature=510'C
.
77.
Stress vs Strain Curves, Strain Rate=0. 0008 (sec ') Temperature =530'C
. . 93
74.
=510'C
. 93
XV
LIST OF TABLES Table
Page
I.
Test Matrix for Weldalite 049
II.
Superplasticity
III.
Average Activation Energy Values for a Constant Strain Range
IV.
Grain Sizes for Weldalite 049
V.
Aspect Ratios for Weldalite 049
VI.
Coefficients for Polynomial
14
Tests Conducted on Weldalite 049
. . . .
.
.
29
. . 70 71
. . 72
' Equation, Strain Rate=0. 0002 sec
94
VII. Coefficients for Polynomial Equation, Strain Rate=0. 0004 sec'
95
VIII. Coefficients for Polynomial Equation, Strain Rate=0. 0006
sec'. . . . . .
96
'. . . . . . 97
IX.
Coefficients for Polynomial
X.
Strain Rate Sensitivity,
Temperature=470'C
98
XI.
Strain Rate Sensitivity,
Temperature=490'C
99
XII.
Strain Rate Sensitivity,
Temperature=510'C
XIII.
Strain Rate Sensitivity,
Temperature=530'C
Equation, Strain Rate=0. 0008 sec
XIV. Activation Energy for Different Strain Rate
101 and Temperature
Ranges
. 102
xvi
NOMENCLATURE
A
b d
D D, e e
G
r 'y
k
L m n
0 T Q
substructure related parameter Burgers vector grain size grain-boundary diffusivity bulk diffusivity grain boundary width true tensile strain true tensile strain rate shear modulus grain-boundary free energy per unit area strain hardening coefficient Boltzmann's constant length strain rate sensitivity strain hardening exponent atomic volume absolute temperature true tensile stress activation energy
1.
1.1
Background is defined as the ability
Superplasticity
of
INTRODUCTION
strain
before failure.
Moreover,
a material
is said to display
if the elongation exceeds 200%. Superplasticity was
characteristics
the 1920's by Hargreaves" elongation
of a material to elongate to high values
and Jenkins.
'
superplastic
first observed in
Later in 1934, Pearson' observed
an
of 1950%.
This phenomenon Sviderskaya'
was not investigated
observed superplastic
and Backofen
with
support
furthermore,
superplasticity;
from colleagues' this
has been the topic
superplasticity
again until
1945,
when Bochvar and
properties in a Zn-Al alloy. In 1962, Underwood'
study
of
completed
an extensive
acted as a forerunner
many
research
and
investigations.
study
on
since then
The highest
recorded elongation, 4850%, was seen in Pb-62%Sn eutectic which was elongated at
a temperature
1.2
of 413K.'
Mechanics of Superplasticity Superplastic
materials
are characterized
by their high strain rate sensitivity
value, m. The high value of m indicates the resistance to the development in the material.
The strain rate sensitivity,
in Equation
1, (which is a simplified
steady state form of the equation) is used to define the relationship
This thesis follows the format of Metallurgical
of necks
Transactions.
between the flow
stress and the strain rate:
a=k4
1.3
Types of Superplasticity There
are basically
environmental.
two
Microstructural
types
of superplasticity:
microstructural
often termed
superplasticity,
micrograin
and
or fine
is the most common type. It is observed in materials which
grained superplasticity,
exhibit a fine grain size when deformed at a slow strain rate and at a temperature
greater
than
deforming
O. ST
makes micrograin hand
is
superplasticity,
superplasticity, at
present
superplasticity
not
which
is
attractive
often
an unfeasible
environment
from
called
On the other
transformational
a commercial
standpoint.
as the load is cycled. But,
of producing a commercial setup makes environmental processing
of
which
is observed in materials that exhibit elongations greater
200% when the temperature is cycled simultaneously
the complexity
This method
into a commercial
a method of industrial importance.
superplasticity
environmental
Environmental than
(T is the absolute melting temperature).
a material is easily implemented
method.
Therefore, only microstructural
superplasticity superplasticity
is
discussed in this thesis.
Micrograin
superplastic
phase and microduplex. grain
alloys can be divided into two types: pseudo single
Pseudo single phase alloys are processed so as to have a fine
size along with fine dispersoids
distributed
throughout
the matrix.
These
dispersoids
grain growth
prevent
alloys can be further
phase aluminum
alloys.
recrystallizing
dynamically
induced
recrystallized
growth
grain
into statically
and
prior to superplastic
occur.
In contrast
In microduplex
materials a thermomechanical
fine grain
size.
structurally
different phases which limits the amount
These materials
that the microduplex
1.4
of the
materials
consist roughly
process is applied to produce a
of
two equal
The processing of microduplex limited elongations
these alloys are termed, entirely
materials for ceramics is
of importance
that are usually observed in these materials.
and recrystallization
"'"
Pseudo Single Phase Alloys for
characteristics
involves
to refine the grain size. Moreover,
pseudo single phase alloys, because they consist almost
of solid solution. The rest of the
the grain boundary
of
of grain growth. The elongations
Processing pseudo single phase alloys for superplastic
of warm working
proportions
exhibit is much less than that of the pseudo single
Processing Dynamically Recrystallizing Superplastic Characteristics
treatments
forming
to produce a fine grain
the process.
size throughout
because
dynamically
fine grain size but left
During the superplastic
deformation.
process, the material dynamically or continuously recrystallizes
phase alloys.
and
recrystallizing
During the forming process both
forming.
hardening
Pseudo single
alloys are recrystallized
alloys are processed to a somewhat
aluminum
unrecrystallized
divided
Statically recrystallized
to a fine grain size prior to superplastic strain
deformation.
superplastic
during
matrix consists
of precipitates
which stabilizes the material against grain growth.
dispersed at
These alloys initially contain a high density throughout
the matrix.
of dislocations. the material
Under normal conditions,
would
continuous
undergo
of dislocations.
movement
of fine particles
However,
i.e. absence of fine second recovery
therefore inhibit recrystallization. deformation
The microstructure superplastic
evenly
pseudo
single phase
Upon heating the material,
due to the
alloys contain
fine
of dislocations
in the early stages
and
of
process, the alloy will recrystallize to a fine grain size.
shows
deformation
phase particles,
and recrystallization
dispersoid particles which act as obstacles and prohibit the motion
the superplastic
distributed
The material is then warm worked which forins a high density
fully
equiaxed
grains
to be enacted.
mechanisms
are necessary
which
for the
As the material deforms, high
angle grain boundaries are formed which are necessary for continuing grain boundary sliding.
This processing
5
Qt I
El o W
td
method as described above is illustrated
Ity
D
I« o
t
5
W
5
d
5
t
P
W
5
RIQR Ql
in Figure
W
~t
D
P
P
Plolt
RoP 5 5 DI
R
t ill
y
Pd 5 tQ
(ED
I
R
P
oI
*
t
I
t
54
P
\
y
3
5
I
Fig. 1 - Schematic of Processing Dynamically Recrystallizing
Alloys.
"
1.
1.5
for Mlcrostructural
Prerequlsites
Strain R
Superplastlcity
Sensitivit
A high
superplasticity.
strain
rate
sensitivity,
This criterion
usually
Typically,
a grain size of less than 10@m is necessary
deformation.
"
mechanisms
such as grain boundary
Presence
of Sec
Moreover,
for
because this is a
the grains
need
as the matrix
preventative
zirconium
for superplastic
so that deformation
sliding can occur.
A fine second phase particle distribution
strength
to be equiaxed
nd Phase
after recrystallization.
techniques
is necessary to prevent grain growth
The second phase particle should be
of
itself.
and
This will reduce cavitation
to reduce cavitation.
In aluminum
are added to promote superplasticity.
formed and stabilize the aluminum
the same order in the necessity
of
alloy, small portions of
Second phase particles of ZrA1, is
alloy against grain growth.
"
of rain Bound The material
deformation
process
is a requirement
of the material's resistance to necking.
measure
Nature
m~0. 5,
in essence defines superplasticity
should
by grain boundary
be processed
for high angle grain boundaries
sliding is the most important
mode
of the
since
superplastic
1.6
Characterization
of Superplastic Deformation Behavior
Logarithmic plots of flow stress versus strain rate produce a sigmoidal curve as shown in Figure 2. The curve can be divided into four different regions.
The
slope of the flow stress versus strain rate graph yields the strain rate sensitivity.
This
from region to region and a high strain rate sensitivity
value changes
flow.
superplastic
0 and
Region
I,
a low
strain
which
Region I generally
rate
show low strain rate sensitivity.
acts as evidence
sensitivity
that diffusional
suggests
complicate the issue even further, Region the strain rate sensitivity
creep is the controlling
0 is characterized
characterizing
microstructure
of the
the
grain elongation
of nearly
mechanism.
To
by the fact that sometimes
flow
in these
regions
goes to unity.
very
These issues
complicated
because
the
characteristic
of
this region is that there is some limited
upon deforming.
At high strain rates, the stress versus strain rate is identified
The strain rate sensitivity controlling
microstructure
for
material is so unstable and can change for different materials.
The main microstructural
recovery
stress
initially decreases as the strain rate decreases but when the
strain rate is further decreased the strain rate sensitivity
make
In Region
for a threshold
In contrast, some materials exhibit a strain rate sensitivity
superplasticity. unity
characterizes
is low throughout
dislocational
this region.
creep(power
as Region
Deformation
law creep).
In this region
is affected by such events as multiple slip, grain elongation,
an increase in texture.
III.
occurs by the
and also
Region II is called the superplastic region and occurs at intermediate
levels. greater.
The strain rate sensitivity
"
in the superplastic
There have been many proposed
region but none have proven microstructural
theories
to be complete
for superplasticity
PIEGION
D
REGION
DIPPUSION
However,
CPIEEP
Grain boundary
occurring.
process.
REGIDN
REG ON
SUPERPLAST C T
LOGE STRA
ROSIER LAW
P
I
CREEP
S
P
*
N
or
many
process. The texture during this
because of the high strain rate sensitivity
are usually observed through the deformation
0.5
to describe this
One is that grains either
features are in agreement with these theories.
region lessens as a result of the high elongation
is important
region is in general that attempt
in this respect.
begin to or become equiaxed through the superplastic
strain rate
P
RATED
Fig. 2 - Schematic of Log(stress) versus Log(strain-rate) Diagram.
"
sliding
values that
1.7
Proposed Models for Rate Controlliag Mechanisms
1.7.1
Diffnsional Accommodation Verrall Model"
Ashb
This theory assumes superplasticity(region rates(where
diffusion accommodated
dislocational
creep is controlling).
switching"
mechanisms
of a superplastic
and results in the preservation
Figure 3 shows the process boundary
sliding
accommodation
II) is a transition between low strain
flow is controlling) and high strain rates(where
At low strain rates deformation
with
of grain switching.
diffusional
of
if the stress level is below
is based on grain
moreover,
the total strain rate.
diffusional As shown in
by diffusional
Ipp
can not occur.
which takes place during the intermediate
flow.
Figure 4
stage which
The form of the equation proposed by Ashby and
accommodation
=
This results in a "threshold stress"
this value grain switching
shows the shape accommodation
Verrall for diffusional
of equiaxed grain structures.
This theory
rates(in region II) there is an increase in the grain-boundary
area as compared to the initial and final states.
is provided
material is achieved by "grain
accommodation;
accounts for more than 99%
Figure 4, at intermediate
and
in Superplastlclty
D
krcPI
is shown below in Equation
I'
— o'o7~ P1 & J
At high strain rates, dislocation creep contribution
Ii II
2.
3'3g
(g) 1
accounts for more than 99%
of the
total strain rate. Equation 3, gives the strain rate for the dislocation creep mechanism.
efe1
Fig. 3 - Ashby
and Verrall Model. '4
Vo
2
I
ete
Otffuel F Iux
ej
votu. e I(
G
Fig. 4 - Grain Switching.
'4
e
1
10
disioc. creep =
o]o A— k7 DrGbI
~
During
the superplastic
region
II, both of the mechanisms
strain, which is described by Equation
coc
1.7.2 1
dk
contribute
to the total
4.
fr. occ
Dislocation Pile-up accommodation d Hutchison
Gj
Model" and Mukh
+ g disioc. creep
within Grains
'
M
1"
The Ball and Hutchison theory predicts that groups of grains slide as units until obstructed
by an unfavorably
oriented
grain.
obstacle until the back stress generated sliding.
Figure 5 illustrates
the pile up
assuming
proposed
begin piling up at the
stops the source and therefore
of the dislocations.
strain rate based on the Ball and Hutchison
Mukherjee
Dislocations
a modification
theory.
to the Ball and Hutchison
that dislocations emerge from ledges in the sliding boundaries.
also theorized that grains slide individually
stops the
Equation 5 predicts the
rather than in groups.
model by
This model
The Mukherjee
11
dt's
Jd
t
P,
i
8
Pl
UP
I
Plm
Y
o
5 P
Fig. 5 - Ball and Hutchison Model.
model is displayed in Figure
is Equation
1.7.3
6. The
I
d
it
"
rate equation according to the Mukherjee model
6.
Dislocation File-Up Accommodation
in the Interfaces
Gifkins Modelo, ii This model is based on grain boundary
sliding accommodation
motion and is known as the "Core and Mantle" modeL
to be free of dislocations and that sliding is due to the movement the grain boundary,
i.e. the
mantle.
by dislocation
The model assumes the core
of dislocations
along
The advantage of this theory is that grain rotation
12
can be predicted.
The Gifkins model predicts Equation 7 as the rate controlling
equation.
/ /
g
Ledge
Fig. 6 - Mukherjee Model
/
/
13
2. 2.1
EXPERIMENTAL PROCEDURE AND ANALYSIS
Alloy Composition
and Sample Processing Details
Weldalite 049, with a composition of A1-4. 75% Cu-1. 3%Li-o.4% Ag-0. 4%Mg-
0. 14%Zr-0. 03 %Ti, was alloy was produced metallurgy
alloy.
techniques.
Upon
heating
first developed at Martin Marietta Laboratories. Aluminum
by Reynolds
in production
Weldalite is a dynamically superplastic
during
recrystallizing
machined
into samples, the shape and dimensions
in Figure
7. The
dimensions
of the
0. 1875-in. (4.763mm)
0 0
1
CT
HIGH
TEMI ERPTVRE
Fig. 7 - Schematic of Test Sample
TE SILE SPEC
of Weldalite were
0.25-in. (6.35mm)
0.094-in. (2.388mm)
0 000
l
to a fine
of which are schematically shown
rolling direction.
samples were prepared in the longitudinal
by ingot
pseudo single phase
the sheets
sample were as follows:
width, and
quantities
stage the alloy recrystallizes
equiaxed grain size. After processing for superplasticity,
length,
" Later, this
MEN
000=
thickness.
gage
All the
14
2.2
Test Matrix for Weldalite 049 Table
I
shows the various tests that were conducted
matrix includes four temperatures(470
on Weldalite.
C, 490'C, 510'C, and 530'C) and four strain-
rates(0. 0002sec' 00004sec' 00006sec' and 00008sec')
Table-I. Test Matrix for Weldalite 049. Constant Strain Rate
The test
Temperature oC
(sec)' Test 1
0.0002
470
Test 2
0.0002
490
Test 3
0.0002
510
Test 4
0.0002
530
Test 5
0.0004
470
Test 6
0.0004
490
Test 7
0.0004
510
Test 8
0.0004
530
Test 9
0.0006
470
Test 10
0.0006
490
Test 11
0.0006
510
Test 12
0.0006
530
Test 13
0.0008
470
Test 14
0.0008
490
Test 15
0.0008
510
Test 16
0.0008
530
Pressure
Psi.
15
2.3
Mechanical Testing The uniaxial testing of superplastic materials as employed in the present work strain-rate,
involves controlling three parameters:
prevent cavitation.
1137 Universal different
testing
(3) Instron
compatible personal computer.
showing
3120 temperature
the four components.
controller,
Figure g, shows the testing
1137. Also Figure 9, is a
using the Instron
and back pressure to
(1) Instron
(2) Instron 3117 split furnace which has three
machine,
zones,
heating
temperature,
The testing apparatus uses four different components:
schematic
Figure 10 is a drawing
and
(4) IBM
of a superplastic specimen
of the experimental
setup,
of a close
of the
up view
retort, which is used to test the specimen under back pressure.
It can be seen from Figure g, that the Instron 1137 is the main component of
the sample.
of
The retort provides the added capability of pressurizing
test facility.
the superplastic
Furthermore,
this retort was designed to withstand
a maximum pressure
1000 Psi. The test system also has the ability to heat the sample to a uniform
temperature.
This is accomplished
the retort. The temperature and thermocouples added capability
by a split zone furnace which is wrapped around
is controlled using an Instron 3120 temperature
which are located inside the retort.
of accurately deforming
the sample
controller
The test system also has the at a constant true strain-rate.
This is facilitated by the use of the IBM compatible personal computer which uses an A to D board to communicate
directly with the Instron 1137 testing machine.
To start with, the specimen to be tested was loaded inside the retort of the Instron
1137. Next,
the retort was pressurized,
using argon gas, to a hydrostatic
17
STAON
3120
T EMP E AF T U A E CONTROLLE RE
INSTAON
SPLIT
0 QC
3117
FURNACE
NSTRON
1137
ARSON TANK TO PAESSURIZE RETOAT
Fig. 9 - Schematic of Experimental Setup
CCMP UTER
TO
CQ TAO STAR IN AATE
18
PULL ROD
G
E
TA
L
M
T
ESSUR C RGON GAST
HTDROSTAT C
C
5 ELL
FUR
CE
Ga P START NG
PO51TION T E
OCOU
LES
TEST SPECIMEN
THERM
OAO
CELL
E M3O3UPLE
FacssuaE FEED-Taau
Fig. 10 - Closeup View of Retort
COOL
I
G
L
I
5 5
N5VLAT
O
E
LO O CE L RE55V E FEED-T R
19 pressure of 400 Psh
The split furnace was preheated
which it was wrapped
temperature
stabilize).
for the temperature
was within a allowable
After the temperature
after
The specimen was then heated to the set
around the retort.
(it takes about three hours
to the set temperature,
Each test yielded a load versus displacement
inside the retort to
limit the test was started.
curve, which was converted to a true
stress versus true strain curve, based on the assumption
that the specimen undergoes
Figure 11 is a typical true stress versus true strain diagram.
uniform deformation.
SAMPLE
-
STRESS
Strain Rate = O.OOOX
VS STRAIN
1/sec
Pi
1.08
1.44
400psi
T=XXX C
12.00
9.60
720 W
Ir
480
In
2.40
0.00 Elongation
036 = XXX
~4
0.72 STRAIN
1.80
Sn/inl
Fig. 11 - Typical Stress vs Strain Diagram
2.4
Instability Ductile materials
start to deform at a nonuniform
cross-section.
As a result,
one region is deformed at a different rate than another section. The faster deforming region is called a neck and this area determines
the ultimate strength
of the material.
20 When a neck developes the cross-sectional area reduces, which increases the localized
stress in this region.
by increasing
However, due to strain hardening
the material strengthens
itself
the number of dislocations after further deformation.
Equation 8 gives the basic relation between the flow stress, strain, and strain rate at a constant temperature
and assuming
Here C, is the material constant. negligible,
steady-state conditions.
If it is assumed
that stain hardening
for any given strain, Equation 9 results.
strain rate sensitivity
is constant or
Likewise, if we assume that the
for a true strain rate Equation
is constant or negligible,
10
results.
o = C, 0
(10) Here C, and material.
C, are
material constants which are dependent
These are not actually constant for nonsteady-state
rate sensitivity,
Equation
a
exponent and strain hardening
12 and 13, respectively.
materials.
of the
The strain
11, can be calculated from Equation 8.
dlrik,
The strain hardening
on the structure
(11)
coefficient are given by Equations
21
Bine,
a
(12)
de,
(12)
de
To derive the instability parameter, the starting point is the basic stress equation which is shown in Equation 14. Next, Equation 15 is derived, which is the derivative
of the
load with respect to length.
P
dP = a dL,
—— dA +A
dL
The equation of state at constant temperature shown in equations
(li)
= aA
da = 0 dL
(15)
is used to find the parameter da/dL, as
16 and 17.
a
=
(1e)
fle, t)
(17)
Substitution
of Equation 17 into Equation 15, results dA
Ba
de
Ba
in Equation
dk
18 as follow:
(18)
22 The following equations are used to predict the basic relationships
between strain,
length, time, and strain rate.
dc
dL
dA
L
A
1 dA A dL
de dL
1
de
Equations
(20)
A A
———
—
1-m-y
1
On an incipient neck or a reduced section, the quantity
) refers to
(23)
6A=A, -A„where the first
the neck, is always positive in tension.
either positive, negative, or zero depending unstable.
(22)
11,13,20, 21, and 22 into Equation 18, Equation 23 results. dA
area(A,
(21)
— 1 dA + A dA A dL Aa dL
d9 dL
By substituting
dA
Adt
dt
(19)
upon whether
However,
5K=A;A, is
the specimen is stable or
When 8A/8A is greater then zero the sample is unstable but when 5A/AA
is negative or equal to zero the specimen is stable against local necking. The quantity
of A/A is always
negative in tension.
2
Equation 24 defines the instability
~lm m
parameter.
(24)
23
I)0 the specimen
If I ~0 then
the specimen is stable against necking.
is unstable.
Figure 12 presents an overview of the instability analysis.
In contrast,
INSTABILITY ANALYSIS FOB MATESIAL AND
1'1'1 A
A
BOTH STAAIN
STBAIN-SATE SENSITIVE
A, 2' A, 2' P2 A
IS
THAT
if
P
dA=
A
dA=
A
wee
2
2
sce
— A
— A
I
I
1
1
sect o
N
Y
dA dA
d
dA dA
B
Fig. 12 - Instability Analysis
2.5
Activation Energy
The principles different temperatures the energy required
and procedures
to determine
the activation
and strain rates are described below.
energy,
Q, at
The activation energy is
to move an atom from one lattice site to another.
Equation 25 gives the general relationship
between flow stress and strain rate
at a constant strain. Equation 26 is derived from Equation 25 and gives the necessary relationship
to find the acflvation energy.
24
(a&)
Came (P/kt)
1) g (— 1no =1n (C) +mink+ —
k
(26)
T
For a constant strain rate, Equation 26 can be graphically represented,
13. line.
r
The activation energy is simply determined
(1/ Temp
Fig. 13 - Graph of ln(stress) vs 1/temp
by measuring
ST.
I
1
ST
I
2
ST
I
3
ST
et
as in Figure
the slope of a given
25
2.6 Mcrostructural 2.6.1
Evaluation
Optical Microscopy An optical microscope was used to determine
of
the possibility
the microstructure
altering
different directions on an uncut sample.
direction(subscript
of
There are three directions of importance:
shows the sample
samples in the gage region and
shown shaded in Figure 15 (the samples the
transmission
electron
Five
G„G„G,, B„and Bz.
B represents samples in the base
For clarity, the actual surface viewed
(grip) region.
2), and transverse
after it has been cut.
different samples were observed using an optical microscope:
Here G represents
Figure 14 shows the
the sample.
1), short transverse(subscript
3). Figure 15,
direction(subscript
in
of the grains
First, the sample was cut using a low speed diamond saw to reduce
in the samples.
longitudinal
the size and shape
in the optical microscope are
"TEM" and "SEM" refer to the samples used
microscope
and
electron
scanning
microscope,
After the samples were cut, they were mounted using clear mounting
respectively).
resin. Then the samples were ground using 240 grit, 340 grit, 400 grit, and 600 grit sandpaper in succession.
After this, the samples were polished using pelion polishing
pad with 3@m diamond paste and a polishing pad with powder
mixed
with
water.
The samples
0.5p
were etched
Alumina Micropolishing with
acid in ionized water.
metallurgical
microscope at a magnification
of 400X. Photographs were
a 35mm camera which was directly attached to the microscope. technique(ASTM
standard)
a solution
of 4%
The samples were then viewed using a Nikon
hydrofluoric
was used to determine
taken with
The linear intercept
the grain size.
The number of
26 grain intercepts for a particular distance were counted on the photographs(20 measurements
were made).
The grain size was determined
different
from these values.
THICLNESS~
LENGTH
TRANSVERSE
DIRECTION SHORT
TRANSVERSE
DIRECTION LDNGITU FINAL
DIRECTION
Fig. 14 - Test Specimen Displaying Directions
QT
6„
Q
QE
6,
QS
GS
QS
TEM
QT
SEM
Q NOTE
THE SURFACES THAT WERE VIEWED ARE SHADED
Fig. 15 - Test Specimen Displaying Location of Microstructural
Samples
27
2.6.2
Scanning Electron Mcroscopy The scanning electron microscope was used to determine the mode of failure the details
criteria by observing
of the fracture surface,
electron microscope was used for the investigation and at two different magnification
by a specially
fabricated
holder
of secondary electrons
collection
A Jeol T-330A scanning
at an accelerating voltage
of 25KV
(200X and 750X). The samples were held in place correctly
which
orientated
the sample
so that
was efficient.
2.6.3 Transmission Electron Microscopy electron
A transmission investigate
and make observations
microscope(Zeiss
10C) was used to extensively
about the internal microstructure
of Weldalite.
A
specimen holder" was used to grind the sample from its deformed thickness down to the approximately
0.3pm.
The grinding was done using a variety of grit papers.
sample was then punched into a 3mm disk using a 'Ladd' micropress. then carried out using two different instruments:
ion milling machine.
mixture.
Thinning was
'Tenupol 2' twin-jet thinner and an
The Tenupol system uses a 20% nitric acid and 80% methanol
The operative conditions for the Tenupol system were as follows: 12 volts, -
15'C, and set on maximum flowrate. sample.
This type of etching creates a doughnut
The second thinning instrument
was an ion milling machine.
specimens
microscope.
were
immediately
observed
using
the
shaped
This techniques
was used to remove any oxide layer that might have formed on the sample. milled
The
transmission
The ion electron
28
3. TEST RESULTS
3.1
AND DISCUSSION
Mechanical Testing The instrument
superplasticity
system
earlier
described
of Weldalite 049.
A series
of
the
0.0008(sec').
and
Values
of
and load were obtained from the Instron machine and then converted into
In view
true stress and true strain.
of true
to characterize
tests were run on Weldalite at four
0.0002(sec'), 0.0004(sec'), 0.0006(sec'),
deformation
used
470'C, 490'C, 510'C, and 530'C; and at four selected strain
different temperatures;
rates;
was
of the large
stress versus true strain for each
Also shown in Appendix the flow stress-strain
I are
number
of tests involved,
of the various conditions are
the plots
in Appendix
I.
the constants for the sixth order equations that describe
relationship.
Table II summaries
the conditions and results for
each test that was conducted on Weldalite 049.
3.2
Instability Analysis
3.2.1
Temperature=470'C The stress versus
temperature
of 470'C are
strain
shown in Figure
was observed at a strain rate of periodically
curves
at different
16. The
strain maximum
for a constant
elongation,
898.4%,
0.0002 (sec'). At this strain rate the flow stress
increases and decreases with strain as shown in Figure 62 (Appendix
This effect is caused by the dynamic competition of hardening present.
rates
As seen in the figure, the polynomial
I).
and softening that is
curve fit does not adequately
describe
29 Table-H. Superplasticity
Tests Conducted on Weldalite 049.
Constant Strain rate
Temperature
('C)
Percent Elongation
Pressure (psi)
(Sec) Test 1
0.0002
470
898.4
Test 2
490
1274. 8
510
1080.4
530
739.6
470
637.2
490
496.4
510
617.2
Test 8
0.0002 0.0002 0.0002 0.0004 0.0004 0.0004 0.0004
530
496.4
Test 9
0.0006
470
579.2
Test 10
0.0006
Test 11
0.0006
510
542. 0
Test 12
0.0006
530
402.7
Test 13
0.0008
470
476. 8
Test 14
0.0008
490
689.6
Test 15
0.0008 0.0008
510
563.6
530
326.0
Test 3 Test 4 Test 5
Test 6 Test 7
Test 16
the actual data.
462. 8
Moreover, the correlation factor, (R„u), is only
0.635
for this test.
The hardening effect, due to which there is a increase in flow stress values, is caused by dynamic grain growth, subgrain activity, and the formation
is a self strengthening necking.
of dislocations.
This
effect in that as the material deforms it develops resistance to
Softening, which is indicated by a drop in flow stress, is caused by recovery
and dynamic recrystallization.
Although,
the polynomial
curve does not adequately
30
Weldalite
-
049
Stress vs Strain Pressure=400ps(
Temperature=470C 25 20
Strain Rate
0.0002
(1/s(
Strain Rate 0.0004 (1/4( Strain Rate
15
s
0.0006
10
(1/s(
Strain Rate (1/sl
0.0008
0.00
0.46
1.38
0/92 Strain
1.84
2.30
Snnn&
Fig. 16 - Stress vs Strain Curves, Temperature=470 C characterize
the experimental
analysis because
curve, this curve fit was still used in the instability
of the difficulty of using
the actual data.
The curves at the three higher strain rates,
0.0008 (sec '), all
showed a uniform hardening
0.0004 (sec '), 0.0006 (sec'),
effect up to the peak stress condition.
After reaching the peak stress, the specimens start to soften and eventually lowest elongation
at a temperature
constant strain rate
of 470'C
and
was
fails. The
476. 8% which was observed at a
of 0.0008 (sec').
The stress versus strain rate curves, which are shown in Figures 17a, 17b, and
17c, were constructed using the data from Figure 16. An incremental strain value of
0. 1 (in/in)
and an initial strain value
of 0. 1 (in/in) was used
in the graph.
starts out low for a strain rate of 0. 1 (in/in) reaching a peak at a strain
The stress
of 0.7 (in/in)
31
Weldalite
049
Temperature 25
-
Stress vs Strain Rate
= 47OC Pressure
=
4OO)&si
0. 1
(in/in&
Strain
0.2
(inhn&
20 Strain
e' i&!
e
.4'
15
0.3
0.4 e
6
/I
10
//
t/&
/,
p—
0.5
0.60
0&40
Strain
0.60
(in/in)
Stra in
0.6
0.20
&inhnl
Strain
7 ~
0 0.00
(iit/In)
Strain
(in/inl
Stra in
1.00 (E-3)
0,7
(inhn)
Rate (1/sec)
Fig. 17a - Stress vs Strain Rate, Temperature=470'C Strain = 0. 1-0.7 (in/in)
Weldalite
049
Temperature
-
Stress vs Strain Rate
= 47OC Pressure
= 4OOt3s&S» '" 0.6 (inhnl
25 Strain
0.9
Strain
s
1.0
..-e
/e 2'
e
(in/in)
e
20
ape
7
——/ v
1.1
/ jyru //ra /jjj
10
t/&
(inhn&
Strain (lii/ln)
Strain 1
//j'
2
(In/ln)
—~— Strain 1.3
0.00
0.20
0.40
0.60
Strain Rate (1/sec)
0/&0
1.00 &E— 3)
Fig. 17b - Stress vs Strain Rate, Temperature=470'C Strain =0.7-1.4 (in/in)
&in/in)
Strain
1.4
(ln/In)
32
049
Weidalite
Temperature
-
Stress vs Strain Rate = 400psi
= 470C Pressure
25
20 Strain
1.5 ill
15
ti
1.6 (ill/ln) Stra in
10
IA
1 /7
+
0.00
0.40
0.20
Strain
0.60
0.80
Rate ()/eec)
(ifl/Ill)
Strain
1.8
(innni
1.00 (5-3)
Fig. 17c - Stress vs Strain Rate, Temperature=470 Strain
(in/)n)
Strain
C
=1.5-1.8 (in/in)
and then decreases.
The strain rate sensitivity was determined
from these curves and
is obtained by calculating the slope for a given strain. In Figure 16, it can be seen that the constant strain rate curves merge with one another at high values of strain.
The instability
below the strains at which the curves merge. and
0.0008 (sec ')
calculations
analysis
is carried out for strains
For example, strain rates
cross each other at a strain of just over
1.4
0.0006 (sec ')
(in/in),
instability
were made at lower strains than this. The reason behind this is that the
strain rate sensitivity
value would become negative beyond the merge point because
there would be a decrease in stress upon increasing
the strain rate.
Figure 18 shows the graph of strain rate sensitivity versus strain which was determined
using Equation
11. Theoretically,
values of strain rate sensitivity
should
33
049
Weldalite
Temperature 2.60
-
Strain Rate
versus
M
= 470C Presstre
= 400psi
2.06
Strain Rate 0,0002 1/S
--4--
1.56
Strain Rate
0.0004 1/s
1.04 A. S
0.52
4/4+ s rre-s-0 s'
s +
0.00
0.00
a
a. e s
0.40
~I'
s. +
0/50
s
Strain Rate
e6 e
/i
0.0006 1/s Strain Rate
0.0008 1/s
s
140
2.00
1.60
STRAIN sn/in)
Fig. 18 - Strain Rate
Sensitivity vs Strain, Temperature=470'C
never exceed one.
As can be seen on Figure
displays values
follows.
of strain rate sensitivity
up to
18, a strain rate of 0.0002 (sec')
2.5. This
The strain rate sensitivity is proportional
anomaly can be explained as
to the difference in stress over the
difference in strain rate. It can be seen from Figure 16 there is a large gap in stress values between strain rates
0.0002 (sec ') and 0.0004 (sec '). This difference
in stress
arises because the flow stress curve at the higher strain rate shows a greater initial amount
of strain
hardening
to increase m artificially. changes,
than that at a strain rate
0.0002 (sec'),
which would tend
The high value of m can also be due to microstructural
processing time at temperatures
due to a slower strain rate, and lastly due
to the fact that the strain rate sensitivity was derived from an expression that does not include the strain hardening
effect.
34 In Figure 18, for a constant strain rate of 0.0004 (sec ') and
Then at higher
(in/in).
strains
due to the material's
sensitivity
the material
the
a strain of
1.4
up to
increase in strain rate sensitivity
show a gradual
specimens
0.0006 (sec '),
shows a decrease in the strain rate
Eventually
lowered resistance to neck development.
due to softening and localized necking the specimens fail.
At the highest value
strain rate(0. 0008 (sec
of 0.75 is observed at a
gradually
strain
of
')) a maximum
this value
drops off at higher strains.
The graph temperature
of
gamma(strain
of 470'C is shown
hardening
in Figure
coefficient)
the four strain rates, the strain hardening
decreased to zero.
versus
strain
13. This figure
shows that at all
coefficient was initially high and gradually
A gamma value equal to zero means that the peak stress
stress versus strain diagram has been reached; is a balance between the strain hardening indicate evidence of
rates the material eventually
for a
19. This curve was derived from the data
from the stress versus strain diagram and Equation
gamma
strain rate sensitivity
0.5 (in/in) but due to softening
furthermore,
and softening
softening by recrystallizing.
of
the
this also means that there
effects. Negative values of At the three highest strain
softens and localized necking causes the gamma values
to decrease drastically causing failure.
At a strain rate
of 0.0002 (sec ')
and
a strain
of 0.8 (in/in), the gamma value is negative but as the strain is increased this value becomes positive.
This situation may be attributed to secondary strain hardening
to grain growth, subgrain activity, and the increase
due
of dislocations.
Figure 20 shows the graph of instability versus strain for a constant temperature
35
049
Weldalite
-
vs Strain
Gamma
= 470C Pressure
Temperature 6.00
= 400psi
a60
Strain Rate
0.0002
)20
(1/s)
Strain Rate 0.0004 (1/S)
4. 4SS-4
—t&0
+.
'4 4
Strain Rate 0.0006 ( 1/s)
Strain Rate
0.0006
—6.00
0.00
0.40
OBO STRAIN
Fig. 19 - Strain
1,60
2 00
(in/rn)
Coefficient vs Strain, Temperature=470'C
Hardening
Weldalite
1.20
(1/s)
049
Temperature 25
-
Instability = 470C Pressure
vs Strain
= 400psi
~
15
Strain Rate
0.0002
(1/s)
Strain Rate
0.0004
0,0006 (1/s) .+
Strain
0.00
0,40
0.60
1.20
1.60
Rate
0.0008
—15
—25
(1/s)
Strain Rate
-5
2.00
STRAIN (in/in)
Fig. 20 - Instability Parameter vs Strain, Temperature=470'C
(1/s)
36
24. At
of 470'C
which was calculated using Equation
of strain
the material is stable, which is indicated by a negative instability parameter,
I.
of 0.0004 (sec')
At strain rates
and
all the strain rates at low values
0.0006 (sec '),
becomes positive at higher levels of strain.
parameter
the value
of
the instability
Shortly after these values
of
strain are increased the specimens fail. The curve for a strain rate equal to
0.0002 (sec ')
type of analysis is on the strain rate sensitivity. value of
I goes to
of 1.4 (in/in) but the sample does not fail
infinity at a strain level
of over 2.2
until a strain
(in/in).
indicates how sensitive this
This is shown by the fact that the
This anomaly arises because
of the
high value
of
strain rate sensitivity(2. 5) exhibited at this strain rate, as discussed earlier.
3.2.2 Temperature
=490'C
Figure 21 is the stress versus strain curves for a constant temperature
490'C. A higher elongation was observed at this temperature, strain
rates, than
Moreover,
the other temperatures.
1274.8% was observed at a strain rate of
a maximum
0.0002 (sec').
of
at any of the tested elongation
of
Similiar to the 470'C
temperature
curve for a strain of 0.0002 (sec'), 490'C at this identical strain rate also
periodically
increased and decreased in flow stress values due to the competition that
exist between
softening and hardening.
higher degree
of
softening
hardening
The three higher strain rates all indicate a
and showed a more distinct difference in hardening
and
forming a curve that had a peak.
One interesting
aspect to this graph was that at a strain rate of
0.0006 (sec')
37
049
Weldalite
-
Stress vs Strain Press(jre=400ps(
Temperat(/re=490C
js
1
6.00
1
4.40
Strain Rate
10.60
0/M02 (1/a& Stren Rate
7%0
Strain Rate 0.0006 (1/a(
0.0004
(1/4(
Strain Rate (1/al
0.0006
a60
000
0.54
1.06 Strain
1.62
2. 16
2.70
an/in&
Fig. 21 - Stress vs Strain Curves, Temperature=490'C the curve had a higher peak than that for the strain rate
there was no instability only negative elongation
values
of 0.0008 (sec'). As a result,
analysis conducted at the strain rate
of strain rate sensitivity
at a temperature
would
of 0.0008 (sec') because
be obtained.
of 49(yC was 462. 8% and was observed at
The lowest
a
strain rate
of 0.0006 (sec '). The stress versus strain rate curves for a temperature
of 49PC are shown in
Figures 22a, 22b, and 22c. As mentioned earlier, this analysis was not be conducted
on the highest strain rate because the flow stress at this strain rate did not surpass the flow stress at was
0. 1 (in/in)
a
strain rate with
of 0.0006 (sec '). The initial
strain for the three figures
a incremental strain of 0. 1 (in/in).
Figure 23 is the strain rate sensitivity versus strain curves for a temperature
38
049
Weldalite
Temperature 1 6.00
-
Stress vs Strain Rate
= 49OC Pressure
=
4OOt&s(
0. 1
(inhn&
Strain
0.2 12.80
enhn)
Strain
0.3
9.60
+
6.40
—e--
0.4
Ul
(In/IA&
Strain Qnhn&
N
e i/&
Strain
05
(inhn&
—~— Strain
3.20
0.6 0.00 0.00
0.40
0.20
0.60
(in/in&
Strain
1.00 0.80 (E-3)
0.7
(rnhn&
Strain Rate (1/aec)
Fig. 22a - Stress vs Strain
Strain Rate, Temperature=490'C
=0. 1-0.7 (in/in)
049
Weldalite
Temperature 1 6.00
-
Stress vs Strain Rate
= 49OC Pressure
=
4OOios(
0.8
(inhn)
Stra in
0.9
+
/ 4
12.80
9.60
I
"//' // 4///
1,0
(inhn&
/
Strain
1.1
(inhrl)
6.40
Strain
3.20
Strain
1.2 1.3
0.00
0.20
0.40
0.60
0.80
1.00 (E-3)
Strain Rate (1/eec&
Fig. 22b - Stress vs Strain
(in/rn&
—6—Strain
I'I
/e / e e/ jt 'e /j//
Strain Rate, Temperature=490'C (in/in)
=0.8-1.4
(in/in)
(in/in&
Strain
1.4
(inhn&
39
049
Weldalite
Temperature 1 6.00
—
Stress vs Strain Rate
= 49OC Pressure
= 400psi
12.80 Strain
1.5
9.60 en e r/I
(inhn)
Strain
1.6
6.40
(ih/in)
Strain
(,7
(in/in)
3.20 0.00
0,40
0.20
0.60
1.00
0.80
&5-3) Strain
Rate (I/sec)
Fig. 22c - Stress vs Strain Rate, Temperature=490'C Strain=1. 5-1.7 (in/in)
Weldalite
049 -
M
Strain Rate
versus
= 49OC Press(re = 400psi
Temperature 2.00 1.60
Strain Rate 0,0002 1/s
1.20
Stra in Rate 0.0004 1/s
080 0.40
Strain Rate 0.0006 1/s
p /r I
/2
i
0
0.00
0.00
0.40
0.80
1.20
1.60
2.00
STRAIN (inhn)
Fig. 23 - Strain Rate Sensitivity vs Strain, Temperature=490'C
40
of 490'C.
All
of the strain rates at this temperature displayed a strain rate sensitivity This again is because, in deriving the strain rate sensitivity,
value greater than unity.
neglecting the strain hardening
All
was an incorrect assumption.
of the
curves showed
versus strain graphs
an initial increase or positive slope on the strain rate sensitivity
which indicates the material is becoming more strain rate sensitive and that resistance
to necking sensitivity,
is high.
the curves decrease in strain rate sensitivity
upon increases in strain. developing
value of strain
After the curves reach the maximum
values at
a
rate
much greater rate
This is evidence that the material is losing its resistance to
necks and that softening and localized necking is soon inevitable.
of 490'C
The gamma versus strain curves for a temperature
are shown
in
Figure 24. These curves show that the specimens initially have a high degree of hardening
which decreases at higher strain levels.
0.0008 (sec') 1.6
of 0.0006 (sec ')
have a large softening effect that occurs at a strain
of just
and
greater than
leads to failure.
The stain rate
0.0002
always has a positive gamma value which corresponds
to a hardening
effect.
(in/in).
(sec')
Strain rates
This softening effect eventually
The analysis was conducted up to a strain of 1.8 (in/in) but the sample, for a strain rate equal to
0.0002 (sec '),
does not fail until a strain
Figure 25 is the instability
of 2.62 (in/in).
versus strain curves for a constant temperature
of
490 C. This graph shows that initially the curves are stable and as the strain is increased the curves gradually tend toward a instability value shows that the samples
at these strain rates eventually
instability corresponding
to an unstable structure.
of zero.
The graph also
obtain a positive value of
The strain rate of 0.0006 (sec ') has
41
049
Weldalite
-
vs Strain
Gamma
= 490C Pressure = 400psi
Temperature
~
3.60
Strain Rata
0.0002
120
&1/st
Strain
Rata
Strain
Rata
0.0004
~s.S-s-s
-IZO
(I/s&
0.0006
&1/S&
Strarr Rata
i
0.0008
(1/s&
—3.60
0.00
040
OBO
1.20
1.60
2.00
STRAIN (rn/in(
Fig. 24 - Strain Hardening Coefficient vs Strain, Temperature=490'C
Weldalite
049
Temperature 50
-
Instability = 490C Pressure
vs Strain
= 400psi
~
30 IO
Strain Rata
0.0002 (1/si Strain Rata
J
00004
-1O
--sr
—Strain
-30 —50
0 00
0.40
0.60
1.20
1.60
2.00
STRAIN (in/in)
Fig. 25 - Instability Parameter vs Strain, Temperature=49PC
&1/s&
Rata
0.0006
(1/s&
42 an instantaneous
attributed
increase in the instability parameter at a strain of
to the strain rate sensitivity
1.6. This can be
versus strain curve because there was a drastic
decrease in the strain rate sensitivity,
3.2.3
Temperature=510'C Figure 26 shows the stress versus strain curves at a temperature
lowest elongation was 542% which occurred at a strain rate of graph shows that the strain rate curve of
stress level than the other strain rates. Appendix
of 510'C. The
0.0006 (sec').
0.0002 (sec') occurs at a
This
much lower flow
The actual data for this curve, Figure 64 in
I, shows that there is dynamic competition between softening and hardening
at high levels of strain.
Moreover, this competition seems to be somewhat balanced
because the stress versus strain curve is nearly a horizontal line. This strain rate was where the maximum elongation,
1080.4%, was observed for a temperature of 510'C.
The three higher strain rates in Figure 26 all have an initial uniform hardening that occurs until the maximum
flow stress is reached.
At the two highest strain rates
the material then softens which eventually
leads to failure.
0.0004 (sec ')
that occurs at
shows secondary hardening
Figures 27a, 27b, and 27c are the curves
rate for a constant temperature rate sensitivity values.
of 510'C. These
The strain rate curve for
a strain of 1.5 (in/in).
of the flow stress versus the
strain
graphs are used to obtain the strain
43
049 - Stress vs Strain 510C Pressures 400ps&
Weldalite Temperaturei 15 12
Strain Rate
0.0002
&1/s)
Strain Rate
ee ti
0.0004
0.0006
/
&h
&1/s)
Rate
Strain
0.0008 (1/s)
/ 0.00
(1/s)
Rate
Strain
6
1.00
0.50
Strain
1.50
2.00
2.50
Sn/in)
Fig. 26 - Stress vs Strain Curves, Temperature=510'C
Weldalite
049
Temperature
-
Stress vs Strain Rate
= 510&: Pressure
= 4OOt)s) 5"an 0. 1
15
&inhn)
Strain
0.2
&inhn)
12 Strain /,
g
//j
// ih
/j
6
0.3
/4" e
';
bnhn)
Strain
—-D
0.4
/.
&inhn)
Strain
0.5
(in/in)
—~— Strain 0.6 0.00
0.20
0.40
0.60
Strain Rate (1/sec)
0.80
1.00 &5-3)
Fig. 27a - Stress vs Strain Rate, Temperature=510'C Strain =0. 1-0.7 (in/in)
(in/in)
Strain
0/r
(IA/IA)
44
Weldalite
049
Temperature
-
Stress vs Strain Rate
= 510C Pressure
= 400t&s( O.B
(inhn)
15 Strain
0.9
(inhn)
12 Strain
1.0
(inhn)
Strtan
1.1
rr
Ui
e
5
— e--
6
(In/In)
Strain
1.2
(in/in)
—~—Strain 1
0.00
0.20
0.40 Strain
0.60
0.80
3
&inhn)
Strain
1.00 —3)
1.4
(ln/ln)
&E
Rate (I/aec)
Fig. 27b - Stress vs Strain Rate, Temperature=510'C Strain =0.8-1.4 (in/in)
Weldalite
049
Temperature
-
Stress vs Strain Rate
= 510C Pressure
= 400psi
15 12
Strain
1.5
(in/in&
Strain (inh
).7
(in/in&
—e—Strain
s U)
1.6
e
6
n&
Strain
15
(inhn&
1.9
(inhn&
—4—Strain
0.00
0.20
0.40 Strain
0.60
Rate (1/aec)
O.SO
1.00
(E-3)
Fig. 27c - Stress vs Strain Rate, Temperature=510'C Strain=1. 5-1.9 (in/in)
45 The curves of the strain rate sensitivity
28. The lowest
strain rate again, as was shown previously
shows values in excess
was derived.
versus strain are displayed
of one which can be attributed to
in Figure
for lower temperatures,
how the strain rate sensitivity
The higher three strain rates show values of strain rate sensitivity
generally below one. The curves seem to have some initial increase in the strain rate sensitivity values which indicates the material is resisting the forming
after the strain increases the material begins to soften.
of necks. of
At the high values
for the strain rate equal to 0.0008 (sec') curve, the strain rate sensitivity increase which is due to secondary
hardening
which delayed
Then strain
values
of a neck
the onset
earlier. Figure 29 shows the curves of gamma versus strain for a temperature
510'C. It can be hardened
seen that the material
and then decrease to approximately
for these strain rates are initially
zero. The strain rate of 0.0002 (sec')
does not show negative values for gamma until a strain of
1.6 (in/in) because
the slope
of the
stress versus strain diagram remains positive undl this strain is reached.
three
strain
rates,
of
strain
0.0004(sec'), 0.0006(sec'),
and
0.0008(sec'),
correlation between dramatic decreases in the strain hardening
show
The
a good
coefficient and actual
failure. For instance, there is a distinctive decrease in the strain hardening coefficient
for a strain rate of 0.0006 (sec') at a strain of 1.7 (in/in); value of strain at which the specimen also failed.
moreover,
This can be attributed
this was the
to the fact
that the specimens all failed in a somewhat ductile manner as depicted by their stress
versus strain relationship.
46
Weldalite
049
Temperature 2.00
-
M
Strain Rate
versus
= 51OC Press(re = 400psi
1.60 Strain Rata
0.0002 1/s 120
Strain Rata
0.0004 1/s Strain Rata
0.0006 1/s
OBO
+
Strain Rata O.OOQB
1/s
040 0.00 0 00
0 60
0.40
t 20
1.60
2.00
STRAIN (in/in)
Fig. 28 - Strain Rate Sensitivity vs Strain, Temperature=510'C
Weldalite Tampa/Brune
049
-
Gamma
vs Strain
= 51OC Pressure = 400psi
6.00
3.60 Stran Rate
0.0002
(1/s) Strain Rata
1.20
0.0004
0.0006
+
-3.60 -6.00
0.00
(1/s)
Strain Rata
—120
0.40
0.60
1.20
1.60
(1/s)
Strain Rata 00008 (1/s)
2.00
STRAIN bn/inl
Fig. 29 - Strain
Hardening
Coefficient vs Strain, Temperature=510'C
47 The instability
versus strain curves for a temperature
of 510'C are
shown in
Figure 30. Like the previous instability graphs, the specimens start out stable, i.e. values, and become unstable previous to failure.
negative instability
0.0008
the curve moves to a more stable condition.
dynamic competition
0.0006 (sec ') strain
The strain rate
(sec ') curve at a strain of 1.3 (in/in) starts to become unstable but due to
curve there seems to be an upperward
On the strain rate
trend to become unstable
at a
of 1.6 (in/in) which is a premature value because the specimen does not fail
until a strain value
of 1.85 (in/in).
At the lowest strain rate this material
become unstable only at a strain of 1.8 (in/in).
049
Weldaiite
-
Instability = 510C Pressure
Temperature 25
vs Strain
= 400psi
15 Strain Rate
P
a.4.
s
i
ee
s e a-s-s-s-
,s
0/&002 (1/s& ~
Strain Rate
0.0004
(1/s&
Strain Rate
0.0006
+
sl
s i
I
-25
0.00
0.40
0.50 STRAIN
Fig. 30 - Instability Parameter
1.20
1.60
(1/s&
Strain Rate
0,0005
—15
2.00
(rn/in&
vs Strain, Temperature=510'C
(1/s&
starts to
48
3.2.4 Temperature =530'C The stress versus strain curves at a constant temperature in Figure
0.0002 strain
31.
A maximum
(sec ').
of 530 C are
of 739.6% was observed at a
I,
As shown in Figure 65 given in the Appendix
curve fit
describes the data.
In Figure
rate of
of
the stress versus
31,
the curve for the strain
rate equal to
0.0008 (sec'),
reaching its peak value the material softened at a much earlier strain than that strain rate
shown
strain rate
for this strain rate had some cycling but the polynomial
diagram
adequately
elongation
0.0006 (sec').
after
of the
326.0%, was observed at a strain
The lowest elongation,
0.0008 (sec '). Figures 32a, 32b, and 32c, which are the stress versus strain rate curves for
a temperature diagrams,
of 530'C,
were used to calculate
strain
rate sensitivity.
similar to the other stress versus strain rate diagrams, strain value
incremental
These
has an initial and
of 0. 1 (in/in).
Figure 33 is the diagram of the strain rate sensitivity versus strain curves for
a temperature
of 530'C. This
graph shows a strain rate sensitivity
greater than unity
for a strain rate of 0.0002 (sec '). It can be seen from Figure 31 that the stress levels present in the strain rate
0.0002 (sec')
curve is appreciable
that are in the other three strain rate curves.
0.0006(sec '), and 0.0008(sec '), in rate sensitivity maximum
rate sensitivity
0.0004(sec'),
Figure 33 all show an initial increase in the strain
value as the strain level is increased.
strain
lower than the stresses
The three strain rates,
value,
which
After the material
is where
the material
reaches its
is the most
49
-
049
Weldalite
Stress vs Strain Pressure=400ps(
Temperature=530C 1
2.00
j
9.60
Strain Rate
0.0002 7.20 tll
e
Rate
Strain
Rate
(T&
1
0.0008
2.40
0.46
0.92
1.38
1.84
(1/s)
Strain
0.0006
4.80
0.00 0.00
(1/s&
Strain Rate
0.0004
/
I
N
( 1/s) (1/S&
2.30
Strain (inhn)
Fig. 31 — Stress vs Strain Curves, Temperature=530'C
Weldalite
049
Temperature 1 2.00
-
Stress vs Strain Rate
= 53OC Pressure
= 4r)r)t)sr st'a'n 0. 1
(in/in)
Strain
0,2
(inhn)
9.60 Stra in
0.3 7.20
0.4 4.80
0.5
0.00
Strain
(rn/in)
—~—Strain 0.6 (in/in& 0.20
0.40 Strain
Fig. 32a - Stress vs
(in/in&
Strain
2.40
0.00
(in/in)
Strain
0.60
Rate (t/sec)
0/50
1.00 (E—3)
Strain Rate, Temperature=530'C
=0.1-0.7 (in/in)
Strain
0.7
(inhn&
50
Weldalite
049 - Stress vs = 530C Pressure
Temperature 1 2.00
Strain
Rate
= 400)&si St' '" 0.8 (in/rn& Strain O.g
9.60
e
1.0
7.20
1.1
N
e
Strain
2.40
—~— Strain
0.00
Stra in
1.3
0.00
0.40
0.20
Strain
Strain
(in/In)
4.80
1.2
Fig. 32b - Stress
(inhn)
Strain
N
Vl
(inhn&
Strwn
+
0.60
1.00
0.80
(E-3)
Rate (1/sec&
vs Strain Rate, Temperature=530 (in/in)
1.4
(rn/in&
(in/in&
(In/In)
C
=0.8-1.4
Weldalite
049
Temperature 1 2.00
-
Stress vs Strain Rate
= 530C Pressure
= 400psi
960 Strain CL
1.5
7.20
(ln/In)
Strain
1.6
rh
4.80
1.7 2.40
0.00 0.00
(inhn)
Strain
0.20
0.40 Strain
0.60
Rate (1/sec)
0.80
1.00 (E-3)
Fig. 32c - Stress vs Strain Rate, Temperature=530'C Strain =1.5-1.7 (in/in)
(in/in)
51
Weldalite
049
Temperature 2.00
-
M
versus
= 53OC Pressure
Strain Rate = 400psi
1.60 Strain Rata
0.0002 1/s 1%0
Strain Rate
0.0004 1/s Strain Rate
0.0006 1/s
OZ0
+
0.00 0.00
120
0.60
0.40
STRAIN
Fig. 33 -
Strain Rate
0.0006 1/s
0.40
1.60
2.00
Iin/int
Strain Rate Sensitivity vs Strain, Temperature=530'C
resistant to necking, the material begins to have a decreasing strain rate sensitivity and
becomes more likely to develope localized necks. Figure 34 is the gamma versus strain curve for a constant temperature
530'C. This figure shows gradually
that the four strain rates were initially strain hardened
decreased to zero.
effects of hardening
The three higher strain rates show a decrease in
and softening.
which can further be seen in Figure
curves softens again and ultimately
The curves of instability
35. This shows
and
This is the point were there is a balance between the
gamma and then after further straining
in Figure
of
show
31.
a increase due to secondary hardening
Eventually
the material
for these gamma
fail due to geometric softening.
versus strain for a temperature
of 530'C are
shown
that the specimens for all the strain rates at low values
of
52
- Gamma vs Strain = 530C Pressure = 400psi
049
Weldalite Temperature 6.00
~
3.60
120
+
Strain Rate 0.0002 (1/al Strain Rate 0.0004 (1/al Strain Rate 0.0006 (1/al Strain Rate
0.0008
-3.60 —6.00
0.40
0.00
080
1.60
1,20
(1/aj
2.00
STRAIN (in/inl
Fig. 34 - Strain Hardening Coefficient vs Strain, Temperature=530'C
Weldalite
049
-
Instability
= 53OC Pressure
Temperature
vs Strain
= 400psi
25 15 Strain Rate
0.0002
,rae. e-e-e a ia a 8
0.0004
+
Strain Rate (1/al
0.0008
—15
0.00
OAO
(1/al
Strain Rate (1/al
0&006
J eI
-25
(1/al
Strain Rate
4
080
1.20
1.60
2.00
STRAIN (in/inl
Fig. 35 - Instability Parameter vs Strain, Temperature=530'C
53 strain are stable.
not until high levels of strain.
In contrast, a strain rate
instability
of 0.7 (in/in)
3.3
of instability
but
of 0.0008 (sec') has
high
The lowest three strain rates show some amount
parameters
at a strain
which indicates unstable structure.
Activation Energy Analysis
3.3.1
Strain Rate=0. 0002 (sec') The highest elongation was observed at the lowest strain rate (0.0002
This value was 1274. 8% which was achieved at a temperature
gives the graph of the stress versus strain at four different temperatures. from the curves that there seems to be a lot
proceeds particularly
at the slower strain rates.
being a dynamically
recrystallizing
of
cycling
sec').
of 490'C. Figure 36 One can see
of the stress as the test
This may be attributed
to the alloy
type and that there are complex microstructural
changes that occur during the test. Specifically, there is dynamic competition between softening
and hardening.
recovery
which
diagram.
Hardening,
Softening
is characterized
is caused by dynamic
as a negative
in the Appendix
type
of extensive cycling
preferable
by a positive slope on the stress
The actual data for a strain rate of 0.0002 (sec ') is available
I, Figures 62, 63, 64, and 65. This is
describe the behavior
and
strain
on the other hand, is caused by dynamic grain growth, subcell
activity, and dislocation activity, and is characterized versus strain diagram.
recrystallization
slope on the stress versus
was observed.
but does provide
the only strain rate at which this
The polynomial the general
to use the actual data but because
of
curve does not adequately
trends
of the curves.
mathematical
complication,
It is the
54
Weidaiite 049 - Stress vs Strain Strain Rate=0. 0002 Pressi3re=400psi 9.00 7.20
898.49'
T=4 70C
5.40
1274.8% T=490C
3.60
T=510C 739.6% T= 530C
1
1.80
0.00 0.00
0.54
1.08
2. 16
1.62
080.4'Yo
2.70
STFtAIN (inhni
Fig. 36 - Stress vs
Strain Curves, Strain
curve fit will be used for activation energy analysis.
polynomial
In Figure
36, it can be seen that the curves of the four different temperatures
show strain hardening
of 470'C
temperature
curves corresponding
0.76
(in/in).
proportional
analysis maximum
up to
a strain of
0.5
(in/in).
After this, corresponding
to a
of strain.
The
the curve starts to soften on increasing
to temperatures
of 470'C
levels
and 490'C cross
over at a strain of
Since the activation energy is measured at constant strain levels and is
of the
to the difference in flow stresses over the difference
the temperatures, temperature
Rate=0. 0002 (sec')
the value
of activation energy
would
be negative
showed a higher stress level than a lower temperature.
for determining
activation
energy
strain up to the crossover point.
has been confined
inverses
of
if a higher
Therefore, the
in this work to a
55 Figure 37 is a graph for a strain rate of 0.0002 energy using Equation
of the
log
(sec').
of stress versus the inverse of the temperature
This graph is used to determine
26. Table XIV,
activation energy that were calculated. versus strain at different temperature
in the Appendix
in Figure
energy versus temperature
39. This
530 C displays the
the values
of
Figure 38 is the graph of the activation energy
From this figure, it can be interpreted
ranges.
that the activation energy is greatest in the temperature
of the activation
the activation
III, shows
range
510-530'C. The graph
range for various levels
figure reinforces the observation
of strain
that the temperature
is shown
range
510-
highest activation energy.
The maximum activation energy value that was obtained for this strain rate was
92.9 KJ/mole. This
was obtained at a strain
of 0.4 (in/in) which was also
at which the maximum flow stress was observed for the 470'C temperature
Weldalite Strain
049
-
In(stress)
vs t /T
Rate=0. 0002 Pressuer 4000~s
--d--
0.1
(rnhn)
Strtpn
02
(rn/rn)
Strain
er'
0.3
4
+.
(inhn)
Strain
0.4
&inhnl
Strain
0.5
&in/in)
Strain
0.6 0.4 0. 12
0. 13 1/Temp
Fig. 37 - Ln(stress)
(1/K)
vs 1/Temp. Curves, Strain
0.14
(E—2)
(inhnl
Strain
0.7
(in/inl
Rate=0. 0002 (sec')
the strain
curve.
56
049-Act. Energy vs Temperature Rate=0. 0002 PressLre=400ps)
Weldalite Strain
80
tr
W
60
lu
40
&u
~
Temp. aaape
EZ3
Temp. )matte
470-esse
Temp. )tenue
4se 6'lsc
ste-e*oc
20
0. I
0.2
0.3 0.4 0.5 0.6 0.7 Strain (inhn)
Fig. 3$ - Activation Energy vs Strain Curves, Strain Rate=0. 0002 (sec')
Weldalite Strain
049-Act. Energy vs Temperature Rate=0. 0002 Press(re=400'
~
100 rl
0. 1
(in/in)
Strain OZ &in/in)
80 fZ43 strain
0.3
60
EZ3
ra
Iii
40
(inhn)
Strain
0.4
&in/in)
Strain
0.5 20
sn/m)
Strain
0.6
470-490 490-5)0 510—530 Temperature Ran()e (0)
(Iil/In)
Strain
0.7
&in/in)
Fig. 39 - Activation Energy vs Temperature Range, Strain Rate =0.0002 (sec')
57
3.3.2
Strain Rate=0. 0004 (sec ') Figure 40 is the curves of the flow stress versus strain for a strain rate equal
to
0.0004 sec '. The four
the material ultimately
of
the test.
is strain
curves, as shown on the figure, indicate that
temperature
harden
to its maximum
stress
level and then soften until
failure. These curves also show a slight amount of cycling towards the end A maximum
elongation
of 637.2%
was observed at this strain rate and
occurred at a temperature of 470'C.
Figure 41 shows the curves temperature
for a strain rate of
activation energy values. strain for different
ranges.
to the stress versus temperature
temperature
curve
Likewise,
Figure 43 is the graph of the
range at different levels
energy is on an upperward
both the temperature
This figure was used to calculate the
Figure 42 displays the graph of activation energy versus
temperature
activation energy versus temperature that the activation
of the log of stress versus the inverse of
0.0004 (sec').
of strain. It can be seen
trend at different levels of stress for
range 470-490'C and 510-530'C. This can also be related back strain
diagram,
is more strain
Figure 40, due to the fact that the 470'C hardened
curve is more strain hardened
than
than that
that
of 490'C
of 530'C.
and the
510'C
58
-
Weldalite 049 Stress vs Strain Strain Rate=0. 0004 Pressure=400ps) 16.00 1
2.80
637.214
T= 470C
9.6O
496.4%
!
/ / / /7r
6.4O
T=490C
6 1 7.2&/r
T=510C
496.
4%%u
3.20
T=530C /'
0.00
0.00
0.80
Orao
1.60
1.20
2.00
STRAIN
Fig. 40 - Stress vs Strain Curves, Strain Rate=0. 0004 (sec ')
Weldalite
-
049
In(stress)
vs t /T
Strain Rate=0. 0004 Press(/re=400psi
S'train
a
4
0. 1
(in/rn&
Strain
0.2
a-
(rn/in&
Strain
0.3
Sn/in)
Strain
0.4
(rn/in)
Strain
0.5
(in/in&
Strain
0.6
(in/rn)
0.5 0, 12
0. 14
0. 13 1/rema
(E-2& (1/K)
Fig. 41 - Ln(stress) vs 1/Temp. Curves,
Strain
Rate=0. 0004 (sec ')
59
Weldalite Strain 100
049-Act.
Energy
va Temperature
Rate=0. 0004 Pressore=400ps)
80
0
~
60
t)
40
Temp. Range
410
ODOC
Tmme
Rmnte
400 01OC
Temp. Range
010-DDOC
III
2O
0.1
0.2
0.3
0.4
0.5
0.6
Strain (in/in)
Fig. 42 - Activation Energy vs Strain Curves, Strain Rate=0. 0004 (sec ')
Weldalite Strain 100 e
049-Act.
Energy
va Temperature
Rate=0. 0004 Presstre=400ps)
Strain
80
0.1
(rn/in)
Strain
0.2
60
(in/ini
Strain
0.3
On/in)
Strain
U)
40
0.4
(in/in)
EZ! Strain
le
W
2O
470—490
490-510
Temneratme
0.5 (in/ n) St.a 0.6 (in/in)
510-530
Range (0)
Fig. 43 - Activation Energy vs Temperature Range, Strain Rate=0. 0004 (sec ')
3.3.3
Strain Rate=0. 0006 (sec ') The true stress versus true strain curves for the different temperatures
constant strain rate
of 0.0006 sec' are given
in Figure
at this strain rate was 579.2% and occurred at a temperature stress occurred at the lowest temperatures
of 470C. The maximum
and was 18 MPa. Figures
log of stress versus the inverse of the temperature
at a
44. The maximum elongations
45a
and 45b
curves for a constant strain rate
0.0006 (sec'). Two
graphs were used because the strain level at which two
constant temperature
curves merged together was relatively
high.
are
of
of the
Figures 46a and
46b are the curves of the activation energy versus strain for constant temperature ranges.
Similarly, Figures 47a and 47b are the curves of the activation energy versus
temperature
range for different levels of strain.
The maximum activation energy that
was observed was 96 KJ/mole which was at a strain
of 1.4 (in/in).
-
Weldalite 049 Stress vs Strain Strain Rate=0. 0006 Pressure=400psi 20 16
/
579.2%
T=470C 462.8% T=490C 542.0% T=510C 436.4% T=530C
I/
/'7'
8
/
0.00
0.40
0,80
1.20
1.60
2.00
STRAIN On/inl
Fig. 44 - Stress vs Strain Curves,
Strain
Rate=0. 0006 (sec ')
61
Weldalite Strain
049
-
In(stress)
vs t /
Rate=0. 0006 Pressure=400p~s
Strain
0.1
SnAn&
Strain
e
0.2
(ln/In)
a Strain
0.3
d
(rnhn)
rl
N
Strtlln
a
0.4
Vl
(inAn)
Strain
0.5
(In/Ilt)
—a — Strain 0.6 0.4 0 13
0, 12
1/Teirar
0.14 (E-2)
(in/in)
Strain
0.7
(in/in)
((/&0
Fig. 45a - Ln(stress) vs I/Temp. Curves, Strain Rate=0. 0006 (sec ') Strain =0. 1-0.7 (in/in)
Weldalite
049
-
In(stress)
vs t /T
Strain Rate=0. 0006 Pressure=400p~s
O. B (inhn)
Strtan
Og SnAn) Strain 1,0 (inhn&
a Vt
Strain
a
1.1
(inhn)
Strain
1.2
Sn/in&
—~— Strain 1.3
0.4 0. 12
0. 13
0.14
(E— 2)
1/Temp
(inhn)
Strain
1.4
(in/in)
(1/K)
Fig. 45b - Ln(stress) vs I/Temp. Curves, Strain Rate=0. 0006 (sec') Strain =0.8-L4 (in/in)
62
Weldalite Strain
049-Act.
Energy
va Temperature
Rate=0. 0006 Pressure=400psi
100 ib
Bo
~
60 IU
40
Temp. Range
ITO-490
Temp. Range
lge 510
Temp. Rasge
510 590
20
0. 1
0.2
0.3 0.4 0.5 0.6 0.7 Strain
&in/in&
Fig. 46a - Activation Energy vs Strain Curves, Strain Rate=0. 0006 (sec ') Strain
=0. 1-0.7 (in/in)
Weldalite Strain 100
049-Act.
Energy
ve Temperature
Rate=0. 0006 Pressure=400psi
Bo
& 110-490
Temp. Range
60
W
40
Temp. Range
I go
510
Temp. Rasge
5 ~ 0-590
4 2O
0.6 09
1.0
1, 1 1.2 Strain &in/inl
1.3
1.4
Fig. 46b - Activation Energy vs Strain Curves, Strain Rate=0. 0006 (sec ') Strain =0.8-1.4 (in/in)
63
Weldalite Strain 100
049-Act.
Energy
vs Temperature
Rate=0. 0006 Pressurer
400' 0.
~
(inhn)
1
Strain
0%
(in/in)
60 60
EZ3
Strain
KH
Strain
ul
40
&u
0.3
(inhn)
0.4
(inhn)
E'iU Strain 0.5 (in/in)
20
Strain
0.6 470 —490
490 —510
Temeerature
Range
510—530
CZ
(inhn)
Strain
0.7
(in/in)
(C)
Fig. 47a - Activation Energy vs Temperature Range, Strain Rate=0. 0006 (sec ') Strain =0. 1-0.7 (in/in) Weldalite Strain
049-Act.
Energy
vs Temperature
Rate=0. 0006 Pressure=400p~
0.8
(inhn)
Strain
0.9
60
&,
60
ui
40
(inhn)
IXV
Strain
EZ3
Strain
1.0
1.1
(in/in)
(inhn)
Strain
1.2
20
(inhn)
Strain
1.3
470 —490
490-5 10
Temeerature
510—530
gnhn)
Strain
1.4
(inhn)
Range (C)
Fig. 47b - Activation Energy vs Temperature Range, Strain Rate=0. 0006 (sec ') Strain=0. 8-1.4 (in/in)
3.3.4
Strain Rate=0. 000$ (sec') Figure 48 displays the curves of the flow stress versus strain for a strain rate
of 0.0008 sec '. This
strain rate displayed
occurred at a temperature
temperature
200%,
all
applications,
of 689.6%
which
of 470'C. The lowest elongation recorded at
which occurred at a temperature strain rate; moreover,
a maximum elongation
of 490'C. The maximum stress observed was 21.6 Mpa this
of all the strain rates tested; was 326% and was observed at a
of 530'C. Since, a
material is termed superplastic
of the conditions tested
displayed
superplastic
if elongations
properties.
exceed
In industrial
materials are only elongated to around 200% to 300% during processing.
This means that the material does not have to elongate much over being superplastic.
Therefore,
the strain
rate should
elongation
is slightly
over the desired
production
of parts more economical by reducing the production time.
be increased
to where the actual testing failure
elongation
for industry.
This will make
Figures 49a and 49b are the log of stress versus the inverse of temperature
curves for a strain rate of (in/in) and end with a strain
0.0008 (sec'). of 1.3 (in/in).
These graphs start with a strain
Figures 50a and 50b are the activation
energy versus strain graphs at different temperature and 51b are the graphs
of 0. 1
ranges.
Likewise, Figures 5 la
of the activation energy versus temperature range diagrams for
various strain levels.
These graphs show that the activation energy is generally high
during the temperature
range
470-490'C. At higher strain levels, the activation energy
increases during the temperature
range 510-530'C. This can be seen in Figure 48
where the material for the 530'C temperature
curve softens earlier than that
of
the
65
510'C. The
maximum
activation
energy was seen in the 510-530'C temperature
interval and was 128. 1 KJ/mole.
Weldaiite 049 - Stress vs Strain Strain Rate=0. 0008 Pressure=400psi 22.00 17 60
1
476.8%
T=470C 689.6% T=490C
3.20
563.6'4
8.80
T=510C 326.0%%d T=530C
4.40
0.00
0.44
0.88 STTV
Fig. 48 - Stress vs
1.32 IN
Strain Curves, Strain
1.76
2.20
unnn)
Rate=0. 0008 (sec')
66
-
Weldslite 049 In(stress) vs 1/T Strain Rate=0. 0008 Pressurer 400ps(
.
Strain
'f
0. 1
a
(inhn)
Strain
0.2
(in/in)
Stra in
0.3
(inhn)
5'tl'a in
0.4
(in/in)
Stre in
0.5
(inhn&
Strain
0.6
(inhn)
05 0. 13
0. 12
0. 14 (E-2&
(1/K)
1/Temp
Fig. 49a - Ln(stress) vs 1/Temp. Curves, Strain Rate=0. 0008 (sec ') Strain=0. 1-0.6 (in/in) Weldslite Strain
-
049
In(stress)
Rate=0. 0008
vs
1 /T
Pressure=400p~&s
0.7 en/i' Strain O.B
Onhn&
Strain
0.9 lii
(inhn)
Strain
e
1.0
V
5
—e--
(In/ln)
Strain
1.1
Onhn)
—~— Strain 1.2
0.5
0. 13
0. 12
0.14
On/in)
Strain
1.3
(in/in)
(E-2) 1/Temp
Fig. 49b - Ln(stress) Strain
(1/K)
vs 1/Temp. Curves, Strain
=0.7-1.3 (in/in)
Rate=0. 0008 (sec ')
67
049-Act.
Weldalite Strain 130
Energy
vs Temperature
Rate=0. OOOB Pressure=400psi
104
I W
78 ill
Temp. R nge
470-4$0
Temp. Range
4$0-$10
KB Trna).
52
Rmam
$10-660
2e
0. 1
0.2
0.3 0.4 Strain
0.5 0.5 0.7
&innn)
Fig. 50a - Activation Energy vs Strain Curves, Strain Rate=0. 0008 (sec ') Strain=0. 1-0.7 (in/in) Weldalite Strain 130
049-Act.
Energy
vs Temperature
Rate=0. OOOB Pressure=400ps)
104
y
Tamp. Range
470 4$0
78
Tmnp.
Range
Tmnp.
Range
4$0-$10
IU
52
61O-$$O
2e
0.8
Org
1.0
1. 1
Strain
(innn)
1.2
1.3
Fig. 50b - Activation Energy vs Strain Curves, Strain Rate=0. 0008 (sec ') Strain =0.8-1.3 (in/in)
68
Weldalite Strain 150
049-Act.
Energy
va Temperature
Rate=0. OOOB Pressure=400psi Strain
0.1
120
(inhn)
Strain
0.2
90
0.3 IU
v
60
Strain
EZ1
Strain
30
0.4 0.5
(inhn) (in/in)
Strain
470—490
490 —510
Temperature
049-Act.
(in/in)
510—530
Rarge (C)
Activation Energy vs Temperature Strain = 0. 1-0.6 (in/in)
Weldalite Strain 150
(inhn)
HEI
0.6
Fig. Sla -
(in/in)
Strain
Energy
Range, Strain Rate=0. 0008 (sec ')
va Temperature
Rate=0. 0008 Pressure=400p~
0.'7
(inhn)
Strain
0.8
(inhn)
120
90
8/ZH
Strain
EK
Strain
0.9 1.0
(in/in)
gn/in)
IU
60
Strain
1.1 u
30
Gn/in)
Strain
)Z
470 —490
490 —510
Temperature
Range
510—530
(inhn)
Strain
1.3
(in/in)
(C)
Fig. 51b - Activation Energy vs Temperature Range, Strain Rate=0. 0008 (sec ') Strain=0. 7-1.3 (in/in)
69
3.3.5
Summary The activation energy values averaged over a strain range, at each strain rate
to chosen temperature
corresponding
ranges are shown in Table
III. It is seen that
generally the activation energy values are the lowest in the temperature
range
of 490-
510'C over a stain rate range of 0.0002 (sec') to 0.0008 (sec'). This suggest that superplastic
049,
deformation occurs with more ease in this temperature
when the strain rate is a variable
As observed
by Kashyap
energy values generally
and
range in Weldalite
factor.
Tangri", for an Al-Cu alloy, the activation
are higher in the higher temperature
average values as discussed above are significantly
range.
However,
the
lower than those represented
for
pure grain boundary diffusion and pure lattice diffusion of aluminum
This suggests
that the superplastic
deformation
in Weldalite
and its alloys. ""
049 is facilitated by
mechanisms
additional to grain boundary sliding, considering the latter as the primary
mechanism.
These additional factors could be the climb of dislocations and recovery
and recystallization
of
the matrix
during
superplastic
deformation.
Kashyap
and
Tangri" have postulated that the activation energy increases where the volume fraction
of CuA1,
in the Al-Cu alloys decreases.
This implies that the microstructural
exert a strong influence on the activation energy. "micromultiplicity" the superplastic
", which
deformation
is where the microstructure stage, the wide variation
energy values seems to be justifiable.
features
Since, Weldalite 049 is subject to changes continuously
observed
during
in the activation
70 Table III - Average Activation Energy Values For a Constant Strain Range Temperature Range
Average Activation Energy Values
'C
3.4
Strain Rate
Strain Rate
Strain
Rate
Strain Rate
0.0002
0.0004
0.0006
0.0008
470-490
26.98
35.33
39.0
77.95
490-510
33.94
44. 10
51.83
34.75
510-530
75.62
41.11
60.85
72.57
Optical Microscopy The grain sizes for the various tests conducted on Weldalite 049 are given in
Table IV according to the region that was observed.
The location of the regions were
pointed out earlier in Figure 15. The grain aspect ratios for the different regions are shown in Table
V.
The grain size for dynamic grain growth, which is indicated by the grain size
in the gage region, temperatures
falls in the range
and strain rates.
of 7-12.5@m over the range of tested
There is no regular relationship
between the grain size and the testing time as seen in Figure
that can be developed
52.
Similarly, the grain size for the shoulder region, which illustrates growth, falls in the range
of 5-8 pm. Like as
in dynamic grain growth, there is no
predictable
relationship
relationship
between grain size and testing time.
that can be developed
The as-received dynamically
3pm. u Therefore, substantial
static grain
for static grain growth regarding
recrystallizing
alloys have a typical grain size
grain growth is observed
in both dynamic
the
of
and static
71 grain growth regions.
The aspect ratio as seen in Table V shows maximum
aspect ratio is below
has occurred throughout
1.5.
the deformation
and retain this structure throughout
relatively close to unity values, the
This acts as evidence that grain boundary sliding process because the grains become equiaxed
the process.
Table IV - Grain Sizes for Weldalite 049
'C
G,
G,
G,
B,
Rate
pm
pm
pm
pm
0.0002
470
8. 16
4, 81
5.74
490
9.66 9.03
11.90
0.0002
9.29
5.42
4.43
0.0002
510
15.00
13.9
9. 19 11.34
7.74
6. 86
0.0002
530
16.25
17.4
19.8
10.83
0.0004
470
8. 13
7.65
7.72
0.0004
490
9.99
9.58
9.28
0.0004
510
10.16
9.63
8.97
8. 13
8.66
0.0004
530
11.61
10.83
10.4
7.64
7.56
0.0006
470
7.02
6. 80
6.53
7.02
0.0006
490
8.03
8.31
8.78
6.22
5.98
0.0006
510
8.50
10.48
8.72
7.56
8.01
0.0006
530
7. 14
6.86
7.97
8. 13
7.57
0.0008
470
5. 84
5.74
6.35
6.64
0.0008
490
7.65
7.31
6.72
5.91
6.22
0.0008
510
7.06
8.86
6.36
7.31
5. 85
0.0008
530
6.72
9. 14
8. 13
8.50
6.84
Strain
Temp.
8. 86
7.22
6.81
72 Table V - Aspect Ratios for Weldalite 049
G, /G,
G,/G,
B,/Bz
0.81
1.18
1.46
0.84
0.97
0.98 1.32 0.82 1.05
1.01
1.22
1.23
1.13
Strain Rate
Temp.
0.0002
470
0.0002
490
0.0002
510
1.08
0.0002
530
0.93
0.0004
470
1.06
0.0004
490
0.0004
510
0.0004
530
0.0006
470
0.0006 0.0006 0.0006
530
0.0008
470
0.0008
490
1.05
0.0008
510
0.80
0.0008
530
0.74
'C
G, /Ga
0.88
1.22
0.99
0.84
1.08
1.03
1.12
1.07
0.94
1.07
l. 13 l. 17
0.92
1.03
l. 12
0.93
490
0.97
0.91
0.95
510
0.81
0.97
1.20
0. 895
0. 86
1.07
l. 33 l. 14
1.02
0.96
1.06
1.31
0.83
1.01
0.94
0.95
l. 39
1.25
1.12
1.24
73
vs Testing 049
G(average)
Time
Weidalita 20
C
0 0
16
E
aH N C C
ts
++
+
+
8
+
+4 4
+
4
0
96
48
Testing
144
192
240
Time (min. )
Figure 52 - Grain Size vs Time Plot for G,„,
B(average)
vs Testing 049
Time
Waldalita
20 C
0 0
16
E 14
N C
8
ts
4
a
+
++ +I.
++
+
48
+
4+ +
96
Testing
144
Time (min. )
Figure 53 - Grain Size vs Time Plot for B,„,
192
240
74
3.5
Scanning Electron Microscopy There are two types of failure surfaces that were observed using the scanning
electron microscope. shear separation
The first is termed unstable plastic flow displaying
at failure.
The second is known as pseudo-brittle
of termination of plastic
shows evidence
At this strain evidently
rate, the specimens
electron microscope
using the scanning
0.0002 (sec') for showed
four different temperatures.
the greatest
brought about by differences in the modes
Figures 54 and 55 are the photomicrographs
490'C, respectively.
fracture which
flow at failure.
The samples that were investigated were limited to a strain rate equal to
evidence of
deviation
in elongation,
of failure. of 470'C
for temperatures
These figures both show characteristics
and
of unstable plastic flow.
Figure 55 shows a more uniform type of unstable plastic flow which explains why the sample displayed
the highest elongation
of
the samples tested.
On the other hand,
Figure 54 does show unstable plastic flow but in a more nonuniform
fashion which
can be linked back to Figures 18 and 19. These figures show that at failure the material displayed a high strain hardening hardening
due to secondary
hardening
coefficient. This infers that the sample was but was also subjected
to necldng
due to
unstable plastic flow.
Figures 56 and 57 are the photomicrographs
530'C, respectively.
These two figures show that the mode
specimens was pseudo-brittle highest temperature
for temperatures
fracture.
510'C
of failure for
and
the two
Figure 57, which refers to the sample at the
tested, showed a worst-case scenario
of this type of failure
which
l
p$ ~e
C'
77 explains
further
temperatures
3.6
why
this specimen
tested at the constant strain rate
the lowest
elongation
of
the four
of 0.0002 (sec').
Electroa Microscopy
Transmission
The photomicrographs microscope
displayed
that were obtained
all show sub-cell structure.
processing conditions but are generally electron photomicrographs,
using
the transmission
electron
The size of the sub-cells vary due to very small.
Figures 58-61 are transmission
one at each strain rate, that were taken on the failed
of Weldalite 049. Also included in the four figures are the diffraction
samples
The diffraction patterns for all the specimens ranged from intense spots to
patterns.
rings with dispersed shows an example
spots
of low
of the latter,
intensity.
The diffraction pattern for Figure 58
while the other three diffraction patterns
60, and 61) all show different combinations of intense spots Intense spots are observed when the diffraction
oriented planes grouped together
(Figure 59,
and diffuse spots in rings.
occurs from a few favorably
(e.g. strong texture or dislocation network). Diffuse
spots in ring formation are observed when there is more uniform dispersion planes (e.g. after recrystallization)
that there is significant activity formation
to recrystallization,
.
of
the
The electron diffraction patterns therefore indicate
within the grains, ranging
from dislocation network
which are competitive processes.
The appearance
of
the particular diffraction pattern seems to be decided by which events, viz. , network formation summation,
or recrystallization, the
"micromultiplicity"
electron
is dominant diffraction
at the time the sample
patterns
occurring during the superplastic
indicate deformation
the
broke.
In
likelihood
of
of Weldalite 049.
llgji
~
%'-'
~p'
82
4. CONCLUSIONS of the investigation
The results characteristics
of a dynamically
to examine
recrystallizing
the
aluminum-lithium
superplastic
forming
alloy(Weldalite
049)
indicate the following:
1.
When tested over a temperature
range of 470'C-530'C, the highest elongation
(1274.8%) is obtained at 490'C, at a strain rate of 0.0002 (sec ').
2.
At low strain rates the true stress versus true strain curves show a large number
of maxima
and minima indicating that there is competition
and softening
during superplastic
deformation.
are not observed which indicates that superplasticity necking by strain hardening.
between strain hardening
At higher strain rates, these features
is controlled by the resistance to
The elongations at higher strain rates are significantly
lower than those at slower strain rates.
3.
The instability
recrystallizing
4.
behavior
alloys, notably
that
of other
dynamically
Alcoa 2090 OE16."
The activation energy values generally tends to increase with increases in the strain
rate.
However,
the activation
general, significantly
Transmission
energy
values obtained
for Weldalite 049 are, in
lower than the activation energy values for pure lattice diffusion
and pure grain boundary
5.
of Weldalite 049 is similar to
diffusion in aluminum
electron
microscopy
alloys.
indicates
microscopic activity, notably recrystallization
the
occurrence
and subcell formation.
of significant These features,
along with the low activation energy values observed, indicates that the superplasticity in this alloy is controlled by microscopic factors in addition to grain boundary
sliding.
83
6.
Optical microscopy
studies indicate that both static and dynamic
occured during superplastic
deformation
of Weldalite 049.
grain growth
84
REFERENCES
1.
F. Hargreaves: J. Inst.
2.
F. Hargreaves
3.
C.M. H. Jenkins: J. Inst. Metal. , 1928, vol. 40, pp. 41-54.
4.
C.E. Pearson:
5.
A. A. Bochvar and Z. A. Sviderskaya: Izves. Akad. Nauk. , 1945, vol. 9, p. 821.
and
Metals. , 1928, vol. 39, pp. 301-327.
R. Hills:
J. Inst.
J. Inst.
Metals. , 1929, vol.
41, pp. 257-283.
Metal. , 1934, vol. 54, pp. 111-124.
6.
E.E. Underwood: J. Metals. , 1962, vol. 14, pp. 914-919.
7.
W. A. Backofen, I.R. Turner, and D. H. Avery: Trans. ASM, 1964, vol. 57, pp. 980-990.
8.
M. M. I. Ahmed and T.G. Langdon: Metall. Trans. , 1977, vol. 8A, pp. 1832-1833.
9.
J.G.
Wang and
10. F. Wakai
11. T.E. Chung 12.
J. Pilling Institute
Amer. Ceramic. Soc. , 1984, vol.
and
T.J. Davis: Acta.
67, pp. 385-409.
1988, vol. 3, pp. 71-76.
Metall. , 1979, vol. 27, pp. 627-635.
and N. Ridley: Superplasticity
in Crystalline
Solids, The
of Metals, London, 1989.
13. O. D. Sherby vol.
R. Raj: J.
and H. Kato: Adv. Ceram. Materials. ,
and
J. Wadsworth:
Materls. Science and Technology,
1985,
I, pp. 925-936.
14. M. F. Ashby
15. A. Ball
and
and
R.A. Verall: Acta. Metall.
M. M. Hutchinson: Met. Sci.
,
J. ,
1973, vol. 21, p. 149. 1969, vol. 3, p. 1.
16. A. K. Mukherjee: Mater. Sci. Eng. , 1971, vol. 8, p. 83. 17. R. C. Gifkins: Metall. Trans. A. , 1976, vol. 7A, p. 1225.
85
18. R.C. Gifkins:
J. Mater.
Sci. , 1978, vol. 13, p. 1926.
19. J.R. Pickens: "Weldalite 049
— Ultra-High
Strength Weldable Al-Li Alloy,
Presented at the Mil Handbook 5 Meeting, April 27,
20
P.J. Goodhew:
of Materials,
21. B.P. 22.
Specimen Preparation
for
publ. , Oxford University
Transmission
"
1988. Electron Microscopy
Press, New York, 1984.
Kashyap and K. Tangri: Scripta Met. , 1985, vol. 19, pp. 1419-1423.
K. A. Padmanabhan
and
G.J. Davies: Superplasticity,
Springer-Verlag,
Berlin,
1980.
23. R.
Balasubramanian:
M. S. Thesis, Texas A&M University,
College Station,
TX, 1991.
24.
L.S. Douskos: M. S. Thesis, Texas A&M TX, 1991.
University,
College Station,
86 APPENDIX
I.
TEST MATRIX RESULTS
WELDALITE STRESS VS STRAIN 28JrrtQ 1 Strain Rate = 00002 1/sec P=400psr
T=470 C GAUGE=O. OQOL
10
0.50 ELONGATION
=
1.50
898.4'/
STRAIN
2.50
2.00
Iin/in/
Fig. 62 - Stress vs Strain Curves, Strain Rate=0. 0002 (sec ') Temperature=470'C ELDALI TE
STRESS
Strten Rate =
19JrnQ
VS STRAIN
0.0002 1/sec
I
P=400psr
T=490 C GAUGE=O. OQOL 1
2.00
9.60 7.20 lp
4 80
2.40
0.00
0.00
ELONGATION
0.55 = 1274.8'Y
1.10 STRAIN
1.65
2.20
(in/mt
Fig. 63 — Stress vs Strain Curves, Strain Rate=0. 0002 (sec ') Temperature=490'C
2.75
87
WELDALITE Strain Rate
T=510
STRESS
VS STRAIN
= 0.0002 I/sec
07MARQ1
P=400psi
C
GAUGE=O. OQOL
10
0.50 ELONGATION
= 1080.4IS
1.00 STRAIN
1.50
2.00
2.50
tin/inl
Fig. 64 - Stress vs Strain Curves, Strain Rate=0. 0002 (sec ') Temperature=510'C WELDALITE STRESS VS STRAIN 12MAR91 Strain Rate = 0.0002 1/sec P=400psi
T=530 C GAUGE=0090L
4.80
3.60
P
2.40
120
0.00
0.00
ELONGATION
Fig. 65 - Stress
0.45 = 739.6%
0.90 STRAIN
1.35
1.80
sn/ta
vs Strain Curves, Strain Rate=0. 0002 (sec ') Temperature=530'C
225
88
WELDALITE STRESS VS STRAIN 06/st91 Strwn Rate = 00004 1/sec P=400osi
T=470 C GAUGE=OOQOL
15 12
0.00 Elongation
0.40 =
0.80
637.
STRAIN
2'%%d
1.60
1.20
2.00
Snhnl
Fig. 66 - Stress vs Strain Curves, Strain Rate=0. 0004 (sec') Temperature=470'C WELDALITE Strain Rate
STRESS
VS STRAIN 17Sngt P=400psi
= 0.0004 I/sec
T=490 C GAUGE=O. OQOL 1
2.00
9.60 7.20
4.80
2.40
0.00 Elongation
0 36 = 496.4'/o
0.72 STRAIN
1.08
1.44
(rn/rnt
Fig. 67 - Stress vs Strain Curves, Strain Rate=0. 0004 (sec ') Temperature=490'C
1.80
89
WELDALITE STRESS VS STRAIN 1 7/ong t Strain Rate = 00004 1/sec P=400psi
T=510
0
GAUGE=O. OQOL 1
2.00
9.60 7.20
I
4.50
2.40
0.00 Elongation
0.40 =
0.50
617.2'/o
STRAIN
1.20
1.60
2.00
(in/inl
Fig. 68 - Stress vs Strain Curves, Strain Rate=0. 0004 (sec ') Temperature=510'C WELD ALI TE Strain Rate
STRESS
VS STRAIN
= 0.0004 1/sec
1 5/sog 1
P=400psi
7=530 C GAUGE=OOgOL
10
0.40 Elongation
Fig. 69- Stress Strain
= 496.4 /o
0.50 STRAIN
1.20
1.60
liri/inl
vs Strain Curves,
Rate=0. 0004 (sec ') Temperature=530'C
2.00
90
STRESS
WELDALITE
Strain Rate =
VS STRAIN 04Nn91 P=400psi
00006 1/sec
T=470 C GAUGE=0. 090L
20 16 12
0.00 Elongation
0 45 =
0.90
5792%
STRAIN
1.35
1.80
2.25
anAra
Fig. 70 - Stress vs Strain Curves, Strain Rate =0.0006 (sec') Temperature =470'C STRESS
WELDALITE
Strain Rate =
VS STRAIN 07Nng1 P=400psi
0.0006 1/sec
T=490 C GAUGE=0. 090L 1
6.00
1280
9.60 6.40
320 0 40
0.00 Elongation
=
462.8%
0.60 STRAIN
1.20
1.60
(in/iril
Fig. 71 - Stress vs Strain Curves, Strain Rate=0. 0006 (sec ') Temperature=490 C
2.00
91
STRESS
WELDALITE
Strain Rate =
00006
VS STRAIN 08/stg 1/seo P=400psl
1
T=510 C GAUGE=O. OQOL 1
4.00
1
120 8.40 5.60
2.80
0.00
0.40
0.00
Elongation
=
0.80
542.0%
STRAIN
1.20
1.60
2.00
(rnhnl
Fig. 72 - Stress vs Strain Curves, Strain Rate=0. 0006 (sec ') Temperature=510'C WELDALITE STRESS VS STRAIN 08/rtg1 Strain Rate = 0.0006 1/sec P=400psi
T=530 C GAUGE=O. OBOL
10
0.00 Elongation
0.35
= 402.8%
0.70 STRAIN
1.05
1.40
(in/inl
Fig. 73 - Stress vs Strain Curves, Strain Rate=0. 0006 (sec') Temperature=530'C
1.75
92
WELDALITE STRESS Strain Rate = 00008
VS STRAIN
I/sec
20meyg t
P=400osi
T=470 C GAUGE=0. 090L
25 20 5
I
10
0.40
0.00 Elongation
0.80
= 476.8%
STRAIN
1.20
1.80
2.00
(inhnl
Fig. 74- Stress vs Strain Curves, Strain Rate=0. 0008 (sec') Temperature=470'C WELDALITE STRESS Strain Rate = 0.0008
VS STRAIN 03/si91 1/sec P=400osi
T=490 C GAUGE =0.09OL 15 12
0.00 Elongation
Fig. 75 - Stress vs
0.44 =
669.6%
0.88 STRAIN
1.32
1.76
(in/inl
Strain Curves, Strain Rate =0.0008 (sec ') Temperature=490'C
220
93
STRESS
WELDALITE
Strain Rate =
VS STRAIN
0.0006 I/sec
24mayg
1
P=400psi
T=510 C GAUGE=O. OQOL
15
12
0.00 Elongation
0.40
0.60
= 563.6rrS
STRAIN
1.20
1.60
2.00
Iin/inl
Fig. 76 - Stress vs Strain Curves, Strain Rate=0. 0008 (sec') Temperature=510 C WELDALITE Strain Rate
STRESS
VS STRAIN
= 0.0006 1/sec
29rnay91
Pe400psi
T=530 C GAUGE=O. OQOL
12.00
9.60 7 20
I
460 2.40
0.00
0.30
0.00
Elongation
=
3260/
0.60 STRAIN
0.90 ('n/mt
Fig. 77 - Stress vs Strain Curves, Strain Rate=0. 0008 (sec ') Temperature=530'C
120
1.50
94
Table VI - Coefficients for Polynomial Equation, Strain Rate=0. 0002 sec'
T =470'C
T = 490'C
T=510'C
-0.247
-0.485
0.529
0.696
ai
26.973
30.025
13.687
10.124
a2
-44. 929
-72.681
-15.127
-23.014
ai
33.479
89.513
-1.495
38.226
-16.456
-55.765
13.790
-35.995
6, 226
16.882
-8.452
16.704
-1, 137
-1.971
1.543
-2.972
0, 635
0.761
0.701
0.941
2. 301
2. 621
2.468
2. 128
5.348
8.063
5.930
3.998
898.4
1274. 81
1080.35
739.64
a5
R„„ o
(MPa)
Elongation
T=530'C
95
Table VH - Coefficients for Polynomial Equation, Strain Rate=0. 0004 sec ' T = 470'C
T = 490'C
T= 510'C
-0. 199
0.513
-0. 186
-0.299
a$
52.557
40.413
35.723
35.411
a2
-90.766
-57.817
-60.021
-67.744
as
125.917
57. 149
103.030
105.031
-124.284
-56.981
-123.940
-116.985
a5
o
(M Pa)
Elongation
T =530'C
61.719
34.029
70.271
66.919
-11.478
-7.729
-14.387
-14.436
0.995
0.998
0, 992
0.993
1.998
1.786
1.970
1.786
14.565
11.241
11.226
8.780
637.2
1496.4
617.2
496.4
96 Table VHI - Coefficients for Polynomial Equation, Strain Rate=0. 0006
T = 490'C
T=510'C
-0.206
0.424
-0. 197
0.478
ai
40.325
23. 198
27.335
24. 359
-4.077
51.439
6.252
-26.274
a3
-36.228
-131.96
-55.614
59.899
13.866
93.897
43.969
-114.180
7.062
-22. 532
-9.808
87.487
-3.518
-0.031
-0.492
-22. 841
0.997
0.997
0.997
0.987
1.916
1.7278
1.859
1.615
17.967
15.444
11.869
9.814
579.2
462. 8
542. 0
402. 8
a5
o
sec'
T = 470'C
„(MPa)
Elongation
T =530'C
97 Table IX - Coefficients for Polynomial Equation, Strain Rate=0. 0008 sec '
T = 470'C
T= 490'C
T=510'C
l. 364
0.081
-0.512
0.033
16.017
37.241
34.649
29.015
a2
147.544
-22. 678
-28. 869
-44. 864
ai
-331.512
-9.162
28.220
163.108
275. 180
11.352
-48.705
-349.654
a5
-102.912
-2. 897
36.544
296.607
14. 196
0.081
-8.998
-86. 154
0.999
0.998
0.996
0.986
1.752
2.0664
1.893
1.449
21.687
14.400
12.846
10.263
476. 8
689.6
563.6
326.0
ai
ii
(MPa)
Elongation
T= 530'C
98 APPENDIX H - STRAIN RATE SENSITIVITY VALUES
Table K - Strain Rate Sensitivity, Temperature=470'C STRAIN VALUES
STRAIN RATE SENSITIVITY
STRAIN RATE
STRAIN
STRAIN RATE
STRAIN RATE
0.0002
0.0004
0.0006
0.0008
0. 1
1.096
0.403
N. A.
0.372
0.2
1.089
0.511
0.386
0. 3
1.166
0.613
0.4
l. 291
0.699
0.5
1.455
0.771 0. 827
0. 144 0.358 0.499 0.575 0.604
(in/in)
0.6
0.581 0.702 0.753 0.755
0.7
1.861
0.872
0. 603
0.723
0.8
2.079
0.911
0.589
0.670
0.9
2.284
0.949
0.607
0.605
1.0
2.445
0.989
0.654
0.534
2.527
1.033
0.722
0.458
1.2
2.490
1.083
0.809
0.371
1.3
2. 308
1.132
0.908
0.253
1.4
1.992
1.167
l. 001
0.067
1.5
1.593
l. 161
1.061
N. A.
1.6
l. 178
1.082
l. 053
N. A.
1.7
0.781
0.889
0.932
N. A.
1.8
0.379
0.515
0.580
N. A.
Table XI - Strain Rate Sensitivity, Temperature=490'C STRAIN VALUES
STRAIN RATE SENSITIVITY STRAIN RATE 0.0002
STRAIN RATE 0.0004
STRAIN RATE
0.0006
STRAIN RATE 0.0008
0. 1
1.148
N. A.
N. A.
N. A.
0.2
1.052
N. A.
N. A.
N. A.
0.3
1.155
0. 131
N. A.
0.4
1.279
0.346
0.5
1.367
0.512
0.6
1.384
0.640
0. 185 0.442 0.611 0.727
0.7
l. 315
0.742
N. A.
0.8
1.167
0.831
0.9
0.963
0.918
1.0
0.736
1.014
0.513
1.121
0.812 0.880 0.944 1.009 1.078
1.2
0.313
1.233
1.144
N. A.
1.3
0. 147
1.325
1.196
N. A.
1.4
N. A.
1.353
1.210
N. A.
1.5
N. A.
1.254
1.156
N. A.
1.6
N. A.
0.934
0.955
N. A.
1.7
N. A.
0.894
0. 128
N. A.
1.8
N. A.
N. A.
N. A.
N. A.
(in/in)
N. A.
N. A. N. A.
N. A. N. A. N. A. N. A.
Table XH - Strain Rate Sensitivity, Temperature=510'C STRAIN VALUES
STRAIN RATE SENSITIVITY
STRAIN RATE 0.0002
STRAIN
STRAIN
0.0004
0.0006
STRAIN RATE 0.0008
0.787
0. 164
0.208
0.975
0. 163
0.206
0.576
0. 135
0. 174
0.634
0. 170
0. 176
0.5
0.648 0.951 1.125 1.282 1.428
0.664
0. 186
0.204
0.6
1.545
0.676
0. 193
0.243
0.7
1.610
0.677
0. 198
0.281
0.673
0.305
0.287
(in/in)
0. 1 0.2 0.3 0.4
0.8 0.9
1.508
0.668
1.0
l. 344
0.664
0.206 0.219 0.241
1.138
0.662
0.269
0.242
1.2
0.930
0.658
0.298
0. 186
1.3
0.758
0.758
0.318529
0. 141
1.4
0.651
0.651
0.318
0. 138
1.5
0.616
0.536
0.282
0.203
1.6
0.640
0.418
0. 187
0.355
1.7
0.670 0.597
0.237
N. A.
0.618
N. A.
N. A.
1.114
1.8
0.309
101
Table XIH - Strain Rate Sensitivity, Temperature=530 STRAIN VALUES
C
STRAIN RATE SENSITIVITY
STRAIN RATE 0.0002
STRAIN
STRAIN RATE
STRAIN RATE
0.0004
0.0006
0.0008
0. 1
0.757
0.447
0.046
N. A.
0.2
1.312
0.541
0. 165
N. A.
0.3
1.568
0.617
0. 157
0.358
0.4
1.686
0.675
0.243
0.418
0.5
1,710
0.712
0.277
0.395
0.6
1.661
0.728
0.258
0.288
0.7
1.558
0.726
0. 197
0. 106
0. 8
1.418
0.708
0.325
N. A.
0.9
1.258
0.681
0.332
N. A.
1.0
1.067
0.663
0.383
N. A.
0.948
0.631
0.378
N. A.
1.2
0. 829
0.617
0.422
N. A.
1.3
0.748
0.600
0.440
N, A.
1.4
0.697
0.541
0.346
N. A.
(in/in)
1.5
0.643
N. A.
N. A.
N. A.
1.6
0.515
N. A.
N. A.
N. A.
1.7
0. 196
N. A.
N. A.
N. A.
1.8
N. A.
N. A.
N. A.
N. A.
102 APPENDIX
III - ACTIVATION ENERGY VALUES
Table XIV - Activation Energy for Different Strain Rate and Temperature
Strain Values
Temp. Range
'C
0. 1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Ranges
ACTIVATION ENERGY(KJ/mole) Strain
Strain Rate
Strain Rate
Strain
Rate
0.0002
0.0004
0.0006
0.0008
Rate
470-490
18.9
13.2
41.8
34.3
490-510
17.5
82.7
51.0
69.8
510-530
42. 4
23.4
-17.2
7.9
470-490
23.8
28.0
41.3
52.6
490-510
48. 1
46. 3
47. 1
510-530
77.5
27. 3
31.3
31.4
470-490
32.7
33.8
35.8
75. 1
490-510
44. 6
48. 0
52.5
38.6
510-530
91.5
35.5
47. 1
32.5
470-490
38.0
39.2
31.8
89.9
490-510
36.5
36.2
58.2
33.4
510-530
92.9
44. 7
51.5
32.2
470-490
36.9
45.4
30.5
97.8
490-510
30.6
24. 3
62. 4
29. 8
510-530
86.2
53.7
52. 1
36.9
470-490
28.0
52.4
31.1
100.4
490-510
28. 8
12.8
510-530
75.2
62. 1
52. 1
48. 8
470-490
10.6
N. A.
33.1
98.9
490-510
31.5
N. A.
65.3
27. 1
510-530
63.7
N. A.
54. 2
67.9
470-490
N. A.
N. A.
35.9
94.6
27.7
103
0.9
1.0
1.2
1, 3
1.4
490-510
N. A.
N. A.
510-530
N. A.
N. A.
58.7
470-490
N. A.
N. A.
38.8
88.5
490-510
N. A.
N. A.
61.5
29.6
510-530
N. A.
N. A.
65.5
113.3
470-490
N. A.
N. A.
41.2
81.5
490-510
N. A.
N. A.
57.0
31.5
510-530
N. A.
N. A.
73.5
124.7
470-490
N. A.
N. A.
43.0
74. 2
490-510
N. A.
N. A.
50.8
32.5
510-530
N. A.
N. A.
80.0
119.9
470-490
N. A,
N. A.
490-510
N. A.
N. A.
42. 6
31.0
27.9
91.4
66.8
510-530
N. A.
N. A.
85.0
108.5
470-490
N. A.
N. A.
46. 1
58. 8
490-510
N. A.
N. A.
31.9
25. 8
510-530
N. A.
N. A.
87.8
128. 1
470-490
N. A.
N. A.
51.4
N. A.
490-510
N. A.
N. A.
17.3
N. A.
510-530
N. A.
N. A.
96.6
N. A.
104
VITA
Jeff Seldenrust was born in Chicago, Illinois on December 11, 1966. After attending MacArthur
and received
graduate
High School in Iving Texas, he went to Texas A&M Univerisity
a Bachelors degree
in Mechanical Engineering.
school at Texas A&M University
to pursue
Mechanical Engineering.
Permanent
Address: 4027 Bountiful Crest Lane Sugar Land, TX 77479
Shortly after, he entered
a Masters
of Science
in
