-
Interface Engineering of the Tungsten-Fiber-Reinforced Tungsten Composites
J. Du*, T. Höschen, J-H. You, Max-Planck-Institut für Plasmaphysik, EURATOM Association, Boltzmannstr.2, 85748 Garching, Germany
* corresponding author: [email protected] (address since 1st Mai 2011 : Forschungszentrum Jülich GmbH, EURATOM Association, 52425 Jülich, Germany)
A toughening method for tungsten is proposed based on the reinforcement of tungsten fibers (Wf/Wm composites) and engineered interfaces.
The interfacial parameter determination results show that selected interfaces satisfy to the interfacial debonding criterion.
The interfacial debonding and fiber sliding were demonstrated by micro-mechanical 3-point bending test.
The predicted stress-strain curve of the Wf/Wmcomposites with multiple fibers agree with the theoretical one, supporting the primary motivation of the thesis.
Motivation: Tungsten/Tungsten composite
A novel toughening method for tungsten (W), was proposed and developed based on the reinforcement of tungsten fibers (Wf/Wm composite) and engineered interfaces. The underlying toughening mechanism is analogous to that of a fiber-reinforced ceramic matrix composite (CMC). This work opened a new pathway to improve the toughness of tungsten as a structural material.
com
posi
te s
tress
composite strain
pseudo-toughnessCMC composite toughening mechanism
• crack deflection• Interface debonding• fiber sliding• energy dissipation
Wf/Wm composite concept
W matrix
W wire
Analysis system:
Single filament (fiber) composite
2 fr
l
f
m
zi s
2 fr
l
f
m
zi s
=150m
:2~3mmH:~0.3mm
Wf with interface
magnetronsputtering
chemical vapor
depositionWf Wf/Wm
cut &polished
Fiber push-out testExperiment Specimen preparation
Carbon600 nm
Cu 170 nmCu 480 nm
Cu/W m
ZrOx/Zr mZrOx/W mErOx/W mEr/W m
ErOx600 nm1000 nm
ZrOx150 nm260 nm450 nm950 nm
Lubricating coatingDuctile coatingMultiple-layer coatingOxide coating
Designed interfaces
20.7
23
20.5
17.315.6
16.718.3
21.9
1616.8
13.1
15.817.2
9.8
0
5
10
15
20
25
ZrOx 150 ZrOx 450 ZrOx 950 ZrOx&W260
ErOx600
ErOx1000
ZrOx/Zrm
ZrOx/Wm
ErOx/Wm
Er/W m Cu/W m Cu 170 Cu 480 carbon
Aver
age
enrg
y ab
sorp
tion
(kJ/
m^2
fiberfiber
Result-Push-out test curve The area below the curve corresponds to the total amount of workdone by the applied load—average energy absorption Δ, kJ/m2
Result-Interfacial fracture energy (i) calibration and debonding criterion verification P
HR
RL
0.00 0.02 0.04 0.06 0.08 0.10 0.120
10
20
30
40
50
Load
(N)
Displacement (mm)
A, Pd
B
C, Pfr
Interface: ZrOx 450Specimen thickness: 0.226 mm
0.05 0.10 0.15 0.20 0.250
500
1000
1500
2000
2500
3000
3500
Stre
ss p
(MPa
)
Specimen thickness H (mm)
23 0.6 J/mi Interface: ZrOx 450
1 12 2
2 1
2 ( 1)f fB H B HR Ri f R
f
Ep e e
B R B
H : Specimen thickness2d
f
PpR
(Liang,1993)
i Mode 2 fracture energy for the debonding event 9.61
5.86
2.89 3 2.992.03
1.23
3.5 3.462.01
7.66
12.34
7.41
0
2
4
6
8
10
12
14
16
ZrOx 150 ZrOx450
ZrOx950
ZrOx&W260
ErOx600
ErOx1000
ZrOx/Zrm
ZrOx/Wm
Er/W m
ErOx/Wm
Cu/W m Cu170 Carbon
Frac
ture
ene
rgy
(J/m
^2)
9.61
5.86
2.89 3 2.992.03
1.23
3.5 3.462.01
7.66
12.34
7.41
0
2
4
6
8
10
12
14
16
ZrOx 150 ZrOx450
ZrOx950
ZrOx&W260
ErOx600
ErOx1000
ZrOx/Zrm
ZrOx/Wm
Er/W m
ErOx/Wm
Cu/W m Cu170 Carbon
Frac
ture
ene
rgy
(J/m
^2)
Fiber fracture
Interfacial debonding
Elastic mismatch
i
f
0
5.0
1
5.0 10
5.1
5.01
Fracture mechanism
He,1989
Debonding criterion
≤≤0.250.25Interface fracture energy i
Fiber fracture energy f (≈ 320 J/m2)
Budiansky 1995
3 22
23 ( 2 ) (2 3 )
3f
mc D D S D D S m mmcA
rc
mc
f f mmc
mc E c E
2 f cD fm m f
iE Ecc E r
2 f
Am m
Rc fc E Ec E
132 2(1 ) /S f f f m f R cm fl r c E E c E r
( / )(1 )f c S f
tR
sf
am
c E l rc E
/sats fa ft c E
Evans 1994
The stress-strain curves is typical for a toughened composite, supporting the motivation of this work.
0
200
400
600
800
1000
1200
1400
1600
1800
0 0.5 1 1.5 2 2.5 3 3.5
Strain (%)
Stre
ss (M
Pa)
mc
sat
y
uFiber pull out
Interface: ZrOx 450Fiber volume: cf=0.6
Budiansky 1995
3 22
23 ( 2 ) (2 3 )
3f
mc D D S D D S m mmcA
rc
mc
f f mmc
mc E c E
2 f cD fm m f
iE Ecc E r
2 f
Am m
Rc fc E Ec E
132 2(1 ) /S f f f m f R cm fl r c E E c E r
( / )(1 )f c S f
tR
sf
am
c E l rc E
/sats fa ft c E
Evans 1994
A toughening method for tungsten is proposed based on the reinforcement of tungsten fibers (Wf/Wm composites) and engineered interfaces.
The interfacial parameter determination results show that selected interfaces satisfy to the interfacial debonding criterion.
The interfacial debonding and fiber sliding were demonstrated by micro-mechanical 3-point bending test.
The predicted stress-strain curve of the Wf/Wmcomposites with multiple fibers agree with the theoretical one, supporting the primary motivation of the work.
Interfacial fracture energy i of investigated interfaces
The main focus of this work lies in the investigation of the interfacial fracture behavior of Wf/Wm composites with various engineered interfaces to demonstrate the feasibility of synthesizing a toughened Wf/Wmcomposite using the CMC toughening mechanism.
Goal and focus of this work
W matrix
W wire
W matrix
W wire
• W fiber, u> 2.5 GPa, u> 2%• Interface thickness m
The fracture properties of the engineered interface are the key factors controlling the overall composite toughness.
Micro-mechanical 3-point bending test (ZrOx 260)
2 m
W fiber topW C
Interface delamination
ca) oxide interface: ZrOx 450
b) ductile interface: Cu 480
c) lubricating interface: C 600
Interface deformation and delamination can cause higher interfacial fracture energy.
1 mmatrix
typical W wire surface
structure
fiber
ZrOx 450
a
ConclusionResult-Crack deflection demonstration Result-Behavior prediction of Wf/Wm composite with multiple fibers
The calculated ratios lie between 0.003 and 0.034. satisfying the 0.25 criterion.
The debonding criterion is satisfied !
specimen thickness: 0.226mm
y f f yield Rc /y f yield fE u f f uc
2.1%u
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