Effect of Bimodal Diamond Particle Size Distribution on Thermal Conductivity of Al/Diamond Composite Fabricated by SPS

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Diamond-particle-dispersed-aluminum (Al) matrix composites were fabricated in a solid-liquid co-existent state by Spark Plasma Sintering (SPS) process from the mixture of diamond powders, Al powders and Al-5mass%Si powders. As the diamond powders, two kinds of powders, monomodal diamond powders of 310 μm in diameter and a bimodal diamond powder mixture of 310 μm and 34.8 μm in diameter, were used. The microstructures and thermal conductivities of the composites fabricated were examined. These composites were all well consolidated by heating in a temperature range between 798 K and 876 K for 1.56 ks during the SPS process. No reaction at the interface between the diamond particle and the Al matrix was observed by scanning electron microscopy for the composites fabricated under the sintering conditions employed in the present study. Although the relative packing density of the monomodal composite decreased from 99.1 % to 87.4 % with increasing the diamond volume fraction in a diamond volume fraction range between 50 % and 60 %, that of the bimodal composite was higher than 99 % in a diamond volume fraction range up to 65 %. The thermal conductivity of the bimodal composite was 455-581 W/mK, which is higher than that of the monomodal composite in a diamond volume fraction range higher than 60 %, and it is 530-581 W/mK in a diamond volume fraction range between 60 and 70 vol%.