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Graphite Reinforced Al with 750 W/mK Thermal Conductivity and Controllable Thermal Expansion: Materials Behavior and Prototype Modeling and Performance
Keywords: Thermal Conductivity, Thermal Expansion, Metal Matrix Composites
The thermal conductivity of discontinuous reinforced metal matrix composites is expected to be less than theoretical because of thermal impedance at the interface. However, we have previously shown that when discontinuous pitch graphite preforms are infiltrated with Al-Si alloys, fiber/matrix reactions result in a low thermal impedance interface. Hence, measured thermal conductivity matches theoretical predictions. The lessons learned were applied to highly crystalline graphite (~1500 W/mK in-plane) reinforced Al alloys which were studied over a range of reinforcement volume fractions. Thermal conductivity values from 640 W/mK to 740 W/mK were measured and varied with the volume fraction graphite. Thermal expansion measurements from ambient to 150C varied predictably from 7 ppm/K to 4 ppm/K respectively. These material properties were used to develop thermal models for applications such as the heat sink for a 1U server and the base of a graphics card cooler. Thermal models of the standard OFHC copper were also developed for baseline comparison purposes. The thermal models were experimentally verified on the 1-U server heat sink for the new material. Initial results indicate that compared to OFHC Cu, heat sinks and spreaders manufactured from the materials evaluated here will have higher thermal performance, 25 % of the density of Cu and will be cost competitive.
James A. Cornie, Chief Technology Officer
Waltham, MA

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