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: j.du@fz-juelich.de (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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