1. FUNCTIONAL MATERIALSPowder Technology Center - PTC 1 Copper based composites reinforced with carbon nanofibers René Nagel, Erich Neubauer ARC Seibersdorf research GmbH Tel.: +43 50550 3378 Fax: +43 50550 2724 E-Mail: rene.nagel@arcs.ac.at www.materials-technology.at

2. FUNCTIONAL MATERIALS 2 Overview:  Introduction – Motivation – Potential  Problem Description & Approach  Experimental Results 1) PM processing 2) Infiltration processing  Conclusion & Outlook

3. FUNCTIONAL MATERIALS 3 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 ModuleLED CPU

4. FUNCTIONAL MATERIALS 4 Overview of Developed Heat Conductive Materials  Diamond based composites (PM) Cu-ZrW2O8 Cu-Cu2O Cu-Carbon fiber Cu-Carbon Nanotube

5. FUNCTIONAL MATERIALS 5 Overview on properties of matrix materials/reinforcements Material  [ppm/K]  [g/cm 3 ] [W/mK] Al22 – 242.7220 - 240 HEAT SINK Matrix Materials Cu16 – 178.9390 – 400 Diamond1 – 1.21500 - 2000 Reinforcements Pyrolytic graphite (long.) = C-Fiber Transversal -0.5 – (-1.0) 27 2.25 -2.31700-2000 10 Graphite (isotropic)~02.2104 - 130 Carbon Nanofibers~ -1 to 0~1 – 1.5~1000-2000 Carbon Nanotubes~ -1 to 0~1 – 1.5~1800-6000 SiC Particle3.7 –53.21~ 150 (270 – 390) ZrW2O8 (negative CTE!!)-8 to -95.1~ 2 Cu – C-fiber composites (PM) 6 – 12 (in plane) 5 - 8250 – 300 (in plane) 150 – 200 (out of plane) ARC Composite Materials Cu – Diamond (PM)8 - 125 - 8300 – 650 Al – Diamond (PM)8 -14~ 3300 - 550 Cu – SiC (PM)8-12~6-7200-250 Cu – ZrW2O8 (PM)6 - 106 - 8150 - 200 Cu-CNF *~126-7~250 (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 2007http://www.ceit.es/interface

6. FUNCTIONAL MATERIALS 6 ProblemsCarbon 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 InterfaceInterface 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

7. FUNCTIONAL MATERIALS 7 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

8. FUNCTIONAL MATERIALS 8 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

9. FUNCTIONAL MATERIALS 9 Results (I): Comparison of microstructure ROUTE AROUTE B

10. FUNCTIONAL MATERIALS 10 Results (II): Comparison of microstructure ROUTE AROUTE B  „Perfect CNF distribution for route A  Clusters of CNF observed in route B resulting in porosity

11. FUNCTIONAL MATERIALS 11 Thermal Properties: ROUTE AROUTE B

12. FUNCTIONAL MATERIALS 12 CTE (@50°C)=12.8 ppm/K CTE (@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)

13. FUNCTIONAL MATERIALS 13 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

14. FUNCTIONAL MATERIALS 14 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

15. FUNCTIONAL MATERIALS 15 First results (I): Wetting of CNF by Cu and Cu alloys Cu alloy CNF Foam Non wetting between CNF and pure CuWetting of Cu alloy

16. FUNCTIONAL MATERIALS 16 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

17. FUNCTIONAL MATERIALS 17 Conclusion (II): Infiltration processing  The use of Cu alloys results in wetting of the CNF felt  First infiltration tests have shown that infiltration is possible BUT  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.

18. FUNCTIONAL MATERIALS 18 Thank you for your attention! Contact Austrian Research Centers GmbH - ARC Functional Materials A-2444 Seibersdorf, Österreich Telefon: +43 (0) 50550 - 3345 Fax: +43 (0) 50550-3366 Contact Person: Dr. Erich Neubauer erich.neubauer@arcs.ac.at POWDER TECHNOLOGY CENTER

19. FUNCTIONAL MATERIALSPowder Technology Center - PTC 19 ANNEX

20. FUNCTIONAL MATERIALS 20 MatrixSubstrateTemperatureContact Angle Cu (1at% Cr)Vitreous Carbon1373 K 41  4 Cu (<0.2at% Cr)Vitreous Carbon1050°C~130 Cu (>0.2at% CrVitreous Carbon1050°C~45 Cu (<0.2at% TiVitreous Carbon850°C~150 Cu (>10at% TiVitreous Carbon850°CClose to 0 Cu (10at% Ti)VC/Pyro-C1180°C/1150°CClose to 0 Cu/Cu+1at%VVitreous Carbon1150°C45/62 Cu (1at% Cr)VC/graphite1150°C /60 min50/45 CuVC/Pyro-C1150°C 136  2, 133  3 CuVC/PMG [1] [1] 1100 139  2, 122  2 Positive Influence of alloying elements on wetting, but…

21. FUNCTIONAL MATERIALS 21..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

22. FUNCTIONAL MATERIALS 22 Thermal Properties of Cu-C-Composites CTE: x-y direction Th. Cond.: z-direction CTE TC

23. FUNCTIONAL MATERIALS 23 Properties of Cu-C-Composites CTE: x-y direction Th. Cond.: x-y-direction TC, CTE

24. FUNCTIONAL MATERIALS 24 Thermal Expansion – Experiment und Modell PITCH Fasern

25. FUNCTIONAL MATERIALS 25 Challenge: Mikro – Nano („Metal-Carbon System“) Model of Haselmann Diameter: 20 µm („micron sized filler“) Diameter : 200 nm („nanosized filler“)

26. FUNCTIONAL MATERIALS 26 Overview of Process Development  Powder Metallurgical Processes (Semi-industrial)  Net-shape processes (Powder Injection Moulding): Pilot Plant  Liquid Phase Infiltration (Lab scale)