J.M. Molina, M. Rheme, J. Carron, L. Weber (Sp), Swiss Federal Institute of Technology, Lausanne (Switzerland)
Composites of aluminium reinforced by SiC are becoming a standard material in thermal management
applications where a low to intermediate coefficient of thermal expansion and high thermal conductivity are
required. Due to ongoing development of electronic components it would be interesting to improve the thermal
conductivity of such composites. A possibility to achieve this consists in replacing SiC by diamond particles. Since
some of these thermal substrates have quite large volumes, the price of diamond is an issue; hence partial
substitution may be interesting. We explore in this work the effect of gradual replacement of SiC by diamond on
thermal conductivity. To this end two series of aluminum matrix composites reinforced with mixtures of diamond
and SiC particles of roughly equal size and a series with small SiC and large diamond particles were produced by
gas pressure assisted liquid metal infiltration. The evolution of thermal conductivity as a function of overall
diamond volume fraction between 0 and 60 percent was measured. Replacing SiC gradually by diamond particles
results in a steady increase of thermal conductivity from 220 W/mK to above 500 W/mK. Introducing large
diamond particles into a composite of small SiC in Aluminium allows to vary concomitantly the CTE and the
thermal conductivity of the composite to reach values significantly improved compared to Al-SiC, with the
possibility to vary the base material cost to comply with market requirements. The influence of the gradual
introduction of diamond particles is compared to the predictions of the differential effective medium scheme
generalized for multiple types of inclusions. Good agreement between experiment and prediction is found.