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FUNCTIONAL MATERIALS Powder Technology Center - PTC

Copper based composites reinforced with carbon nanofibers

René Nagel, Erich Neubauer

ARC Seibersdorf research GmbH Tel.: +43 50550 3378Fax: +43 50550 2724

E-Mail: rene.nagel@arcs.ac.atwww.materials-technology.at

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Overview:

Introduction – Motivation – Potential

Problem Description & Approach

Experimental Results 1) PM processing2) Infiltration processing

Conclusion & Outlook

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Electronics need cooling…

Market for electronic´s cooling is increasing

New cooling solutions are required => Materials with high thermal conductivity (low CTE) are necessary

High Power Module LED CPU

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Overview of Developed Heat Conductive Materials

Diamond based composites (PM)

Cu-ZrW2O8

Cu-Cu2O

Cu-Carbon fiber

Cu-Carbon Nanotube

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Overview on properties of matrix materials/reinforcementsMaterial [ppm/K] [g/cm3] [W/mK]

Al 22 – 24 2.7 220 - 240 HEAT SINKMatrix MaterialsCu 16 – 17 8.9 390 – 400

Diamond 1 – 1.2 1500 - 2000

Reinforcements

Pyrolytic graphite (long.) = C-FiberTransversal

-0.5 – (-1.0)27

2.25 -2.3 1700-200010

Graphite (isotropic) ~0 2.2 104 - 130

Carbon Nanofibers ~ -1 to 0 ~1 – 1.5 ~1000-2000

Carbon Nanotubes ~ -1 to 0 ~1 – 1.5 ~1800-6000

SiC Particle 3.7 –5 3.21 ~ 150 (270 – 390)

ZrW2O8 (negative CTE!!) -8 to -9 5.1 ~ 2

Cu – C-fiber composites (PM)6 – 12

(in plane)

5 - 8 250 – 300 (in plane)

150 – 200 (out of plane)

ARCCompositeMaterials

Cu – Diamond (PM) 8 - 12 5 - 8 300 – 650

Al – Diamond (PM) 8 -14 ~ 3 300 - 550

Cu – SiC (PM) 8-12 ~6-7 200-250

Cu – ZrW2O8 (PM) 6 - 10 6 - 8 150 - 200

Cu-CNF * ~12 6-7 ~250 (500)

* A part of R&D activities related to Cu-CNF are performed within EU STREP Project: „INTERFACE“ (http://www.ceit.es/interface) which started 2007

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Problems Carbon fibers (dia:10 µm, 100-500µm) Carbon Nanofibers (dia:100-200nm, 1-500µm)

Selection of suitable raw materials (different suppliers & qualities)

Data sheet of different carbon fibers are available, thermal, mechanical properties are available from measurements

Characterisation of CNF properties is not easy, only rare experimental data are available, there are different suppliers, to get reproducible quality is not easy (thermal properties!)

Separation and dispersion of short fibers in the matrix material

Optimisation of conventional blending techniques is sufficient, coating of fibers provides an advanced solution, fiber breakage has to be taken into account

To coat the CNFs seems to be the most appropriate way to get a homogenous distribution, mechanical milling (damage of fibers?), dispersion techniques with surfactants

Alignment/ Orientation/Anisotropy

Fiber aspect ratio of 1:10 to 1:100 results in an orientation of the fibers during PM processing => anisotropy of properties

Alignment of CNFs during PM processing is not confirmed yet, extrusion results in a prefered alignment of CNFs

Densification of the composite

Optimisation of processing conditions with regard to densification and interfacial reactions

Remaining porosity is higher, interfacial reactions must be controlled with high precision, analysis of interface difficult; low CNF loading can be realized by PM process using CNFs, high loading of CNF only achievable via liquid phase infiltration of pre-forms

Interface Interface plays an important role for mechanical and thermophysical properties

Interface plays an essential role to exploit the potential of the reinforcement => using of alloying elements and/or coated CNFs

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Copper – Carbon Nanofiber Composites:

Cu coated CNF+

Cr or Ti powder

PVD (Cr, Mo) coated CNF+

Cu powder

Route A: Electro chemical coating of Cu on CNF Admixing of „Active elements“

Route B: „Active element“ directly deposited on CNF Admixing of Cu powder

Dispersion of CNF in copper matrix: =>using of chemical coating techniques to deposit the matrix material (copper)

on the CNF

Reduction of Thermal Contact Resistance between Copper and CNF =>Interface „design“ between copper matrix and carbon nanofiber necessary

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Processing: Powder Metallurgical (PM) process

Hydraulic pressure

Vacuum chamber

Graphite Heater

Graphite die

Graphit Punch

Powder

Graphite Punch

Chemical Coating/“decoration“ of CNF with Cu

1. Coating/Mixing

2. Hot Pressing 3. Composite

PVD coating (Mo) on CNF

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Results (I): Comparison of microstructure

ROUTE A ROUTE B

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Results (II): Comparison of microstructure

ROUTE A ROUTE B

„Perfect CNF distribution for route A Clusters of CNF observed in route B resulting in porosity

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Thermal Properties:

pca

0 20 40 60 80 100 1200

20

40

60

80

100

120

140

160

180

200

+5%+14%

Th

erm

al C

on

du

ctiv

ity [W

/mK

]

PVD "nominal" coating thickness [nm]

Cr Mo

0 1 2 30

50

100

150

200

250

300

350

+20% +22%

Th

erm

al C

on

du

ctiv

ity [W

/mK

]

Alloying Content [wt.%]

Ti Cr

ROUTE A ROUTE B

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CTE (@50°C)=12.8 ppm/KCTE (@250°C)=14 ppm/K

Coefficient of thermal expansion (CTE)

Reduction of CTE by addition of CNF was achieved (12.8 ppm/K) Further reduction expected by increase of the CNF volume content High temperature applications (>300°C) might lead to a degradation of

the interface (optimisation necessary)

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Conclusion (I): PM processing „perfect“ CNF distribution is necessary and can be realised by the copper

coating on the CNF Both concepts: PVD coating of fibers with „active“ element and alloying of

„active“ elements showed significant improvements compared to pure Cu-CNF composites (up to 20 % in thermal conductivity)

Further improvements (up to 100%) are expected from: Use of better quality of CNF material (lower impurity, high temperature treated CNFs) Increasing of CNF content from approx. 20 vol% to 40 vol.% Optimisation of the content of the „active“ element Optimisation of processing/sintering conditions

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Liquid Phase Infiltration of CNF felts: concept Infiltration process would allow to realise composite materials with a

higher CNF loading (40vol% or higher) => higher thermal conductivity and lower CTE

Larger Parts can be manufactured (compared to PM) Main Problem: No wetting between carbon/CNF by copper and high

Thermal Contact Resistance between Copper and CNF =>

Approach: using of „designed“ copper alloys which promote wetting and form a good thermal and mechanical interface in combination with proper selected processing conditions

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First results (I): Wetting of CNF by Cu and Cu alloys

Cu alloy

CNF Foam

Non wetting between CNF and pure Cu Wetting of Cu alloy

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Increasing reaction between Cu-Alloy and CNF

First results (II): Infiltration of CNF with Cu alloy

Metal

CNT pre-form

Pressure

Alloying Content/Contact Time between melt and CNF requires a careful optimisation to avoid gradients and reaction products (total consumption of CNF) due to severe reaction between CNF and melt

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Conclusion (II): Infiltration processing The use of Cu alloys results in wetting of the CNF felt First infiltration tests have shown that infiltration is possibleBUT Further optimisation (of alloy composition and process) is necessary to

allow a complete infiltration and to avoid too severe reactions between the alloying elements and the CNF felt

„Quality“ of CNF felt (its high thermal conductivity) is not confirmed yet Thermal analysis of composite materials will be necessary to assess

the performance.

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Thank you for your attention!

Contact

Austrian Research Centers GmbH - ARC

Functional Materials

A-2444 Seibersdorf, ÖsterreichTelefon: +43 (0) 50550 - 3345Fax: +43 (0) 50550-3366

Contact Person:

Dr. Erich Neubauererich.neubauer@arcs.ac.at

POWDER TECHNOLOGY CENTER

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FUNCTIONAL MATERIALS Powder Technology Center - PTC

ANNEX

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FUNCTIONAL MATERIALS

Matrix Substrate Temperature Contact Angle

Cu (1at% Cr) Vitreous Carbon 1373 K 414

Cu (<0.2at% Cr) Vitreous Carbon 1050°C ~130

Cu (>0.2at% Cr Vitreous Carbon 1050°C ~45

Cu (<0.2at% Ti Vitreous Carbon 850°C ~150

Cu (>10at% Ti Vitreous Carbon 850°C Close to 0

Cu (10at% Ti) VC/Pyro-C 1180°C/1150°C Close to 0

Cu/Cu+1at%V Vitreous Carbon 1150°C 45/62

Cu (1at% Cr) VC/graphite 1150°C /60 min 50/45

Cu VC/Pyro-C 1150°C 1362, 1333

Cu VC/PMG[1] 1100 1392, 1222

Positive Influence of alloying elements on wetting, but…

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FUNCTIONAL MATERIALS

..negative influence on the thermal conductivity of the matrix

only ~0.8 wt. Ti lead to a 50%(!) reduction of the thermal conductivity of the copper matrix

0 1 2 3 4 5 60

50

100

150

200

250

300

350

400

P

Au

Zn

Ti

Pd

Ther

mal

Con

duct

ivity

[W/m

K]

Alloying Element [wt.%]

Ni

0,0 0,2 0,4 0,6 0,8 1,0100

150

200

250

300

350

400

P

Au

Zn

Ti

Pd

Ther

mal

Con

duct

ivity

[W/m

K]

Alloying Element [wt.%]

Ni

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0 50 100 150 200 250 3000

2

4

6

8

10

12

14

16

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Kurze Pitch-Kohlefasern (verkupfert) Kurze Pitch-Kohlefasern (gemischt) Kurze PAN-Kohlefasern (verkupfert) Kurze PAN-Kohlefasern (gemischt) Lange PAN-Kohlefasern (verkupfert) Infiltration von Kohlefaserfilzen

CT

E (

20 -

150

°C

), 1

0-6 [

K-1]

Wärmeleitfähigkeit, [W/mK]

Kurze Pitch-Kohlefasern

Kurze PAN-Kohlefasern PAN

CF-Filze

Lange PAN-Kohlefasern

Zielbereich

Thermal Properties of Cu-C-CompositesCTE: x-y directionTh. Cond.: z-direction

CTE

TC

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0 50 100 150 200 250 300 350 4000

2

4

6

8

10

12

14

16

18

CT

E (

20 -

150

°C

), 1

0-6 [

K-1]

Wärmeleitfähigkeit, [W/mK]

Kurze Pitch-Kohlefasern (verkupfert) Kurze Pitch-Kohlefasern (gemischt) Kurze PAN-Kohlefasern (verkupfert) Kurze PAN-Kohlefasern (gemischt) Lange PAN-Kohlefasern (verkupfert) Infiltration von Kohlefaserfilzen Kupfer

Kurze PAN-Kohlefasern

PANCF Filze

Kurze Pitch-Kohlefasern

Lange PAN-Kohlefasern

Zielbereich

Properties of Cu-C-CompositesCTE: x-y directionTh. Cond.: x-y-direction

TC, CTE

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Thermal Expansion – Experiment und Modell

PITCH Fasern

0 10 20 30 40 50 60 700

2

4

6

8

10

12

14

16

18

20

22

24

CT

E, 2

0 -

15

0 °

C, [

10-6

K-1]

PITCH-type carbon fibres, [Vol-%]

FEM model (XY-direction) FEM model (Z-direction) Experimental data (XY-direction) Experimental data (Z-direction)

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Challenge: Mikro – Nano („Metal-Carbon System“)

1E-13 1E-12 1E-11 1E-10 1E-9 1E-8 1E-7 1E-6 1E-5 1E-4150

200

250

300

350

400

450

500

550

600

Th

erm

al C

on

du

ctiv

ity [W

/mK

]

Thermal Contact Resistance [m2

W/K]

1000 W/mK 100 W/mK 10 W/mK

22

1

22

12

i

thi

m

ii

i

thi

m

i

i

thi

m

ii

i

thi

m

i

mc

rR

VrR

rR

VrR

1E-13 1E-12 1E-11 1E-10 1E-9 1E-8 1E-7 1E-6 1E-5 1E-4150

200

250

300

350

400

450

500

550

600

Th

erm

al C

on

du

ctiv

ity [W

/mK

]

Thermal Contact Resistance [m2

W/K]

1000 W/mK 100 W/mK 10 W/mK

Model of Haselmann

Diameter: 20 µm („micron sized filler“) Diameter : 200 nm („nanosized filler“)

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Overview of Process Development

Powder Metallurgical Processes (Semi-industrial) Net-shape processes (Powder Injection Moulding): Pilot Plant

Liquid Phase Infiltration (Lab scale)