Research On Preparation And Thermal Conductivity Of Diamond/Al Composites

Due to the traditional electronic packaging materials have became increasingly unable to meet the demand, Diamond/Al composite materials as a new generation of electronic packaging materials, have exhibited broad application prospects. Cryogenic treatment as a specific heat treatment, has attracted more and more attentions, which is attributed to the simple process, no pollution. In order to prepare Diamond/Al composite materials with high thermal conductivity, one way is to continue to explore and improve the preparation process of materials, while another way is to conduct the cryogenic treatment on the composite material.The Diamond/Al composite materials were prepared by powder metallurgy liquid phase sintering and then the composite materials were carried out by the cryogenic treatment. The density of Diamond/Al composite materials was measured by Archimedes drainage method and the laser thermal conductivity instrument was used for testing the thermal conductivity of the composites. What is more, the scanning electron microscope was applied to observe the microstructure of composite materials and the phase constitution of materials was determined by the X ray diffraction analysis.The effect of sintering temperature, volume fraction, surface titanizing and cryogenic treatment on the density and thermal conductivity of Diamond/Al composites was systematically investigated. The theoretical value of thermal conductivity of Diamond/Al composites was also calculated, the main results and conclusions were as follows:(1) At the sintering temperature of 875 degrees centigrade and the volume fraction of 20%, the thermal conductivity of the composites was the highest, up to 243 W/(m·K).(2) The thermal conductivity of Diamond/Al composites increased with the improvement of sintering temperature. At the sintering temperature of 875 degrees, the thermal conductivity reached the highest, and the thermal conductivity of composites began to decrease with the sintering temperature rised to 900 degrees.(3) The thermal conductivity of Diamond/Al composites increased with the improvement of volume fraction and then decreased. When the volume fraction of diamond increased from 10% to 20%, the thermal conductivity of the composites increased. When the volume fraction of diamond increased to 30%, the thermalconductivity of the composites decreased due to the increase of pore and interfacial thermal resistance.(4) According to the H-J model, at the calculated volume fraction of 10%, 20%,30%, the thermal conductivity of the composites was 255 W/(m·K), 308 W/(m·K),369 W/(m·K) respectively. The experimental value was much lower than the theoretical value, which showed that the thermal conductivity of diamond reinforces aluminum matrix composites has still far from being developed, which was largely due to the large thermal resistance between diamond and aluminum.(5) Due to the inferior wettability of diamond and aluminum, surface modification of diamond was conducted by salt bath plating Ti on the diamond surface. The density of Diamond-Ti/Al composites improved, the combination of diamond and aluminum strengthened,the inferior wettability increased. But only the thermal conductivity of Diamond-Ti/Al composites possessed the volume fraction of 10% improved obviously,while the thermal conductivity of the composites showed a decline trend at the volume fraction of 20% and 30% Diamond-Ti/Al. It may be due to many interfaces introduced,the interface thermal resistance increased significantly.(6) Diamond/Al composite materials have been volume shrinkage with the decreased of temperature during the cryogenic process. The pores were reduced,because the porosity and other defects in the composites were plastic flow due to the volume shrinkage. So the density and the thermal conductivity of the composites improved. When the volume fraction of diamond reached to 20%, the thermal conductivity of composites increased from the original to 269 W/(m·K), enhanced by10.70%.