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Diamond based Metal Matrix Composites with high Thermal

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EIDGENГ–SSISCHE TECHNISCHE HOCHSCHULE LAUSANNE
POLITECNICO FEDERALE DI LOSANNA
SWISS FEDERAL INSTITUTE OF TECHNOLOGY LAUSANNE
Г‰COLE POLYTECHNIQUE
FÉDÉRALE DE LAUSANNE
Emerging materials for Thermal Management
Al und Cu based diamond composites
L. Weber
Laboratory for Mechanical Metallurgy
Ecole Polytechnique FГ©dГ©rale de Lausanne (EPFL)
CH-1015, Lausanne, Switzerland
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LD
B
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IG
LD
ht
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co
lig
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se
su
n
h ea t flo w d e ns ity [W /cm 2 ]
10000
6480
1000
3640
100
2050
10
1152
1
648
0.1
364
0.01
205
e q u iv a le n t b la c k b o d y s u rfa c e te m p e ra tu re [K ]
su
The heat is on!
The heat is on!
small active component
transient heating
small active component
permanent heating
cold air flow
spreading/absorbing
the heat
spreading and transfer
large active component
permanent heating
cooling plate/circuit
mostly transfer
Solution:
Solution:
Solution:
phase change
materials
High l in plane
High l through
plane
heat pipes
Medium/high l
through plane
Typical requirements on substrate or baseplate materials
•
CTE similar to that of GaN and Si (3-5 ppm/K)
(passive cycling) or slightly higher (active cycling).
•
High thermal conductivity, l [W/mK]
пЃ¤ пЂЅ
•
High thermal diffusivity
•
Sometimes: electrical conductivity
•
Structural properties (stiffness, strength)
l
cp пѓ— пЃІ
Candidate materials
Metals:
CTE too high
Ceramics:
“no” electrical conductivity,
too brittle, CTE too low
=> obvious choice:
composites
Composite concepts using carbon material
Chopped Carbon
short-fibres
Continuous Carbon
fibres
Graphite flakes
Common forms of
Carbon
Carbon nanotubes
and nanofibres
Diamond (particles
and fibres)
Diamond price
Raw material prices 2007:
[US$/litre]
Platinum
Gold
Palladium
C-Nanotubes
Silver
CBN
HC carbon fibres
Tungsten carbide
Tungsten
Ni-Superalloys
Molybdenum
Titanium diboride
Nickel
Aluminium nitride
Titanium
Tin
Copper
Silicon carbide
Alumina
Aluminium
800’000.380’000.150’000.12’500.4’100.3’000.2’400.1’300.750.700.680.500.450.256.225.100.72.50.40.6.-
Industrial diamond price 1994
(after Ashby&Jones):
>1’000’000.- [US$/litre]
Industrial diamond price 2005:
10’000.- down to 600.- [US$/litre]
The making of diamond composites
Liquid metal infiltration process
Alternative routes:
• hot pressing of
powder mixtures
• hot pressing of
coated particles
Pressure infiltration apparatus
• Cold wall vessel (250 bar, 200°C)
Inner side of the wall in contact
with a water cooled heat shield
• Induction heating
(using a graphite susceptor)
• primary vacuum pump
(0.1 mbar)
100 mm
• Crucible can be lowered on
quench (directional solidification)
Selected diamond grit
•
Mono-crystalline diamond
•
Low nitrogen level
•
Relatively large size (>100Вµm)
Net-shape fabrication
Ag-Diamond composites
1. Pure Ag + 60 %-vol diamonds (100Вµm)
•
Low thermal conductivity (270 W/mK)
•
High coefficient of thermal expansion (≈17ppm/K)
2. Ag-Si alloy + 60 %-vol diamonds (100Вµm)
•
High thermal conductivity (>700 W/mK)
•
Low coefficient of thermal expansion (≈7ppm/K)
Cu-Diamond composites
1. Pure Cu + 60 %-vol diamonds (200Вµm)
•
Low thermal conductivity (150 W/mK)
•
High coefficient of thermal expansion (≈16ppm/K)
2. Cu-B alloy + 60 %-vol diamonds (200Вµm)
•
High thermal conductivity (>600 W/mK)
•
Low coefficient of thermal expansion (≈7ppm/K)
Matrix alloy development
• What is it that makes an alloying element an
“active” element
• How much active element do we need to get the
right interface?
• And what does this quantity of active element do to
the matrix properties?
Effect of active element on CTE
Active elements are needed to form carbides at the
Metal/diamond (carbon) interface
Ag-Si: thermal conductivity
After infiltration
L.Weber, Metall. Mater. Trans. 33A (2002) 1145-50
Ag-Si-X: alloy requirements
The ternary alloying element X should have/generate
• “no” solubility in solid Ag
Ni
пЂґ
Fe
пЂґ
Mn
пЂё
• some solubility in liquid Ag
пЂґ
пЂё
пЂґ
• reduced Si-activity in the solid state
пЂґ
пЂґ
пЂґ
пѓњ weak silicide-forming element
Ag-Ni binary system
1400
•
Ni content limited to
0.3-0.4 at-%
•
Resistivity increase due to
Ni<0.05µΩcm (after HT @
T<700В°C) and is maximum
about 0.4 µΩcm after HT @
950В°C.
liquide
te m per a tur e [K ]
1300
liquide + (Ni)
1200
(Ag)
1100
(Ag) + (Ni)
1000
Ladet (1976)
900
Stevenson & Wulff (1962)
this study
800
0
0.2
0.4
0.6
Ni-content [at-%]
0.8
1
Ag-Ni-Si: Si activity
700В°C
0
Acker (1999)
Tokunaga (2003)
-10
-20
NiSi2
-30
NiSi
ВІG
f
[kJ /m o l]
Kaufmann (1979)
Ni3Si2
-40
-50
-60
0
0.2
0.4
0.6
x Si [-]
0.8
1
Ag-Ni-Si: thermal conductivity
450
1200
400
th erm al con d u ctivity [W /m K ]
te m per a tur e [K ]
1100
1000
900
800
Ag-2at-%Si
Ag-0.5Si
Ag-0.25Si
700
350
300
250
200
150
Ag-2at-%Si
Ag-0.5Si
100
Ag-0.25Si
Ag-0.3Ni-0.25Si
Ag-0.3Ni-0.25Si
50
measurements
0
600
0
1
2
3
пЃІ [__cm]
∆ ²[µΩcm]
4
5
700
800
900
1000
temperature [K]
Typical situation after infiltration
1100
Kinetic effects: Al-diamond
Thermal
conductivity
CTE
GPI
SC
660
110
10-12
17-25
Interface study of Al-Diamond composites
Comparison of GPI and Squeeze Casting
Influence of diamond volume fraction
on CTE
Al-SiC
Interesting CTE range can be
achieved with mono-modal
particle size distribution
пѓћLow pressure infiltration is
possible
monomodal bimodal
Influence of diamond volume fraction
electrical conductivity
0.5
Going from 60 to 75
0.45
pct vol diamond
n o rm a liz e d e l. c o n d u c tiv ity [-]
0.4
reduces the el.
0.35
conductivity by a
0.3
factor >2!
0.25
0.2
5 Вµm, angular
12 Вµm, angular
30 Вµm, angular
58 Вµm, angular
100Вµm, angular
bimodal 3Вµm/30Вµm, angular
bimodal 5Вµm/30Вµm, angular
bimodal 5Вµm/58Вµm, angular
bimodal 12Вµm/30Вµm, angular
3-P SCS (spheroids, aspect ratio 0.275)
mean-field approach (spheroids, aspect ratio 0.275)
differential scheme (spheroids, aspect ratio 0.275)
5 Вµm, acicular
5Вµm acicular
29 Вµm angular
5 Вµm, slip cast
0.15
0.1
0.05
0
35
40
45
50
55
60
fraction non-conducting phase [vol.-%]
65
70
Importance of the interface transfer problem
Electrical conductivity:
• High phase contrast
• No effect of interface
resistance
=> no effect of phase region size
and field-line distortion
Thermal conductivity:
• low phase contrast
=> Effect of interface resistance
Effective particle properties
Effective particle thermal
conductivity:
l d ,eff пЂЅ
1пЂ«
ld
ld
пЂЅ
ld
1пЂ« B
h bd r
Various models (extension to finite volume fractions):
пѓ¦пЂ пѓ¶пЂ пѓ¦пЂ пѓ¶пЂ l d ,eff
ld
l c пЂЅ f пѓ§пЂ l m ,
, h bd , r,V p пѓ·пЂ пЂЅ gпѓ§пЂ l m ,
,V p пѓ·пЂ lm
lm
пѓЁпЂ пѓёпЂ пѓЁпЂ пѓёпЂ Indirect measurement of the ITC —
size effects
Small particles:
1000
co m po site con du ctivity [W /m K ]
900
• Higher strength
800
700
• Better machinability
600
500
• Lower thermal cond.
400
300
Exp Ag-Si/diamond
200
DEM; h=6.6 10^7 W/m2K
100
0
0
20
40
particle radius [
60
80
Вµ m]
100
Conclusions
•
Metal diamond composites are a promising material for next
generation thermal management solutions.
•
They can exhibit twice the conductivity of pure silver, while
having a coefficient of thermal expansion similar to
semiconductor devices.
•
The interface is extremely important for both, thermal
conductivity and coefficient of thermal expansion.
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