L. Weber (Sp), R. Tavangar, Ecole Polytechnique Fédérale de Lausanne (Switzerland)
Ever increasing requirements for heat dissipation capacity in thermal management of electronic devices have
created considerable interest in materials with very high thermal conductivity combined with a tailored coefficient
of thermal expansion. Composites of diamond and copper are very promising in this regard yet suffer from
inherently weak interaction at the diamond copper interface. To improve this situation active elements have to be
added to the copper matrix. Unfortunately, these active elements decrease the intrinsic thermal conductivity of
the copper matrix and may build a continuous carbide interlayer at the copper diamond interface that reduces the
effective conductivity of the diamond. We present in this contribution a detailed study of the effect of chromium
and boron additions to the copper matrix in diamond reinforced composites made by gas pressure infiltration. We
screen the range of active element additions in order to study the evolution of the CTE and the thermal
conductivity of the composite. We find that the transition from low (120 W/mK) to high (>600 W/mK) thermal
conductivity happens at the same active element concentration where the CTE drops from the matrix value
(roughly 16 ppm/K), rationalized by weak bonding of the diamonds, to a much lower value, i.e. 10 ppm/K for Cu-
Cr and 6.5 ppm/K for Cu-B. The former value is still surprisingly high while the latter is in good agreement with
elastic composite theory. We compare the active element concentration at which the transition appears in the two
alloying systems with the thermodynamic stability limit of the carbide in contact with the Cu-based melt.