Transcript Hierarchy of levels

PROPERTIES OF TWIST EXTRUSION
AND ITS POTENTIAL FOR SEVERE PLASTIC
DEFORMATION
Y. Beygelzimer, V. Varyukhin,
S. Synkov, D. Orlov,
A.Reshetov, A.Synkov,
O.Prokof’eva, R.Kulagin
Donetsk Institute for Physics and Technology
National Academy of Sciences of Ukraine
72 R. Luxembourg, Donetsk, 83114, Ukraine
1
Twist Extrusion: Why care?
Kinematics of TE is substantially different from
that of other SPD processes (like ECAP and HPT).
New potential for investigating and forming new
structures with new properties.
2
Experimental investigation of TE kinematics
1. We used experimental vizioplasticity
method
(E. G. Thomsen) . Metal
flow were reconstructed from crosssections of the specimen with fibres
stopped in the die.
2. We refined this method by
incorporating two natural
conditions:
-metal volume remains constant;
-metal flow is limited by the surface
of the die.
Advantage: method takes into
account the actual rheology of
metal and real friction conditions.
1
5
25
30
3
Main Findings
• As in HPT and ECAP, deformation in TE is performed
through simple shear.
• There are multiple shear planes, unlike in HPT and
ECAP. These planes are perpendicular and parallel to
the specimen axis.
•There are vortex flow with stretching and mixing
within the deformation centre
•There are four well defined deformation zones with
different properties of metal flow
4
Deformation Zones 1 and 2
Located at the two ends of the twist part of the die.
Simple shear in the Transversal plane (T) as in HPT.
Shears in zones 1 and 2 have opposite direction.
T
1
2
Strain: from e ~ 0.0 on the axis to e ~ 1.0 ÷1.5 on the periphery
5
Strain accumulation
Zones 1 and 2
Cu, 20oC
2
1
Strain accumulation
along the die in a
characteristic point
where zones 1 and 2 are
responsible for most of
the deformation.
6
Deformation Zone 3
Located in the twist part of the die between zones 1 and 2
Simple shear in the rotating Longitudinal plane (L)
= 250  300
3
=250 
300
Strain: e ~ 0.4 0.5
L
2 1
L
7
Strain accumulation
Zones 3
Cu, 20oC
3
Strain accumulation
along the die in central
point where zone 3 is
responsible for the
deformation.
8
Deformation Zone 4
Located in the twist part of the die between zones 1 and 2
Simple shear in the peripheral layer (1÷2 mm thick)
Al-0.13%Mg
4
Al-0.13%Mg
Strain: e ~ 2
We thank Dr. Berta (University of Manchester, UK) for macrostructures b), c)
9
Cu, 20oC
Strain accumulation
Zone 4
4
Strain accumulation
along the die in a
peripheral point
10
Accumulation Strain at TE (Cu, 20oC)
11
Controlling metal flow in TE
Strain distribution and
deformation zones
boundaries strongly
depend on
• the geometry of die’s
cross-section,
• inclination angle 
• rotation angle 

By varying these parameters, one can obtain given
inhomogeneous strain. This is of interest for (1) investigating
the effects of strain gradient on the evolution of material
structure, as well as (2) obtaining gradient structures.
12
Accumulation strain for 1 pass TE (Cu, 20oC)
=50o, =80o
=35o, =80o
=50o, =80o
=50o, =80o
Smoothing of structure and properties
during maltipass TE
Despite the nonuniformity of deformation, subsequent TE
typically leads to uniform structure and properties. This is due to
(1) mixing of metal and (2) stabilization of structure and
saturation of properties if strain becomes greater than saturation
level es
499.0
449.5
449.5
Cu 99,9%
350.5
400
350.5
400
301.0
350
-15
400.0
450
0,2YS,
, МPа
MPa
400.0
450
МPа
0,2 ,YS,
MPa
499.0
301.0
350
-10
-5
0
X Ax
is
5
10
15
-8 -6
-4
8
46
2
-2 0
-15
xis
YA
-10
-5
0
X Ax
5
is
After 2 passes
10
15
6
24
0
-4 -2 is
-8 -6
Ax
8
Y
After 4 passes
Mean
Min
Max
Range
Mean
Min
Max
Range
419
385
462
77 (18%)
426
403
450
47 (11%)
Joint work with Dr. Korshunov, Sarov, Russia
14
Stabilization of structure and saturation of
properties during TE
300
es
99.9%Cu
400
YS and UTS, MPa
80
300
60
Elongation
Reduction in area 40
YS
UTS
200
100
0
20
0
1
2
3
4
0
Elongation and Reduction in area, %
100
True Stress, MPa
250
ED
YS
UTS
Elu
Elf
es
YS
UTS
Elu
Elf
80
200
60
150
40
100
20
50
0
0
1
2
3
Number of TE passes
4
Elongation, %
TD
99.99% Al
0
99.99% Al
Number of TE passes
Joint work with Dr. Korshunov,
Sarov, Russia
1 TE pass
4 TE passes 15
Joint work with Prof. Horita, Kyushu University, Fukuoka, Japan
Zone where strain is above the
saturation threshold es=2 (1 pass)
e
16
Zone where strain is above the
saturation threshold es=2 (2 pass)
e
17
Zone where strain is above the
saturation threshold es=2 (3 pass)
e
18
Zone where strain is above the
saturation threshold es=2 (4 pass)
e
19
Zone where strain is above the
saturation threshold es=2 (5 pass)
e
20
Two main routes of TE
Two orientations of the die (, ) lead to two main routes of TE
CD
Route I: CD+CD
CD
CCD
Route II: CD+CCD
CD-clockwise die
CCD- counterclockwise die
21
Two main routes of TE
Route I: CD+CD
Route II: CD+CCD
Plane T
T
Plane T
T
2A
A
L
L
Plane L
0
1
Number of passes
2
Plane L
0
1
Number of passes
2
22
Route II overcomes saturation
CP-Ti
(grade 2)
300oC
=45o
Route I
, 
Route II
, 
Different loading paths can
lead to different structures
and properties. In
particular, using route II
allows one to increase the
yield threshold of Ti after it
saturates in route I
Joint work with Prof. Rack, Clemson University, USA
23
Vortex and Mixing
Deformation Zones 3 and 4 form
a vortex-like flow which
stretches metal particles.
perpendicular crosssection
The stretching increases with
subsequent TE passes as long
as the dies have a constant
direction (all clockwise or all
counter-clockwise)
24
Stretching
(initial)
25
Stretching
Вытягивание
(1 pass, counter-clockwise die)
26
Stretching
Вытягивание
(2 passes, counter-clockwise die)
27
Stretching
Вытягивание
(3 passes, counter-clockwise die)
28
Passes with alternating directions create folds
CD

CCD

, 
2 mm
We thank Dr. Milman for sharing the microstructure.
29
At a finer scale, folds form due to instability
of shear planes
Initial
After one pass TE
Aluminum
Joint work with Prof. Milman, Kiev, Ukraine
30
Alternating stretching and folding leads
to mixing, as in Smale’s horseshoe
Initial specimen
stretching
After several passes
folding
Final specimen
31
So why should we care about Twist Extrusion?
32
• TE has already been successfully used to obtain
UFG structure with good properties in Al, Cu, Ni
and Ti alloys (more at http://hunch.net/~yan).
• Most importantly, TE opens new possibilities for
investigating and forming new structures with new
properties, mainly due to four factors.
33
Factor 1: Two new shear planes in the volume
of the specimen
L
TE
ECAP
34
Factor 2: Vortex-like flow with stretching and
mixing of metal particles
This is of interest for
(1) homogenization (2) mechanochemical reactions
35
Factor 3: Two main routes of TE
which can be combined with any SPD or metal forming
processes (for example: ECAP, rolling, extrusion) to
broaden the space of possible loading paths.
ECAP
TE
I
A
B
C
II
BA
BC
36
Factor 4: New technological possibilities
ECAP
TE
Obtaining profile
or
Metal waste reducing
hollow specimen
Twist die
F
37
We hope that TE
will find its place
among other
SPD techniques
38
We hope that TE
will find its place
among other
SPD techniques
If anyone wants
to talk about TE,
[email protected]
39