Processing and thermal properties of Al/AlN composites in continuous solid-liquid co-existent state by spark plasma sintering

Aluminum nitride-particle-dispersed aluminum-matrix composites were fabricated in a unique fabrication method, where the powder mixture of AlN, pure Al and Al-5 mass%Si alloy was uniquely designed to form continuous solid-liquid co-existent state during spark plasma sintering (SPS) process. Composites fabricated in such a way can be well consolidated by heating during SPS processing in a temperature range between 798 K and 876 K for a heating duration of 1.56 ks. Microstructures of the composites thus fabricated were examined by scanning electron microscopy and no reaction product was detected at the interface between the AlN particle and the Al matrix. The relative packing density of the Al/AlN composite was almost 100% when volume fraction of AlN is between 40% and 60%. Thermal conductivity of the composite was higher than 180 W/mK at an AlN fraction range between 40 and 65 vol.%, approximately 90% of the theoretical thermal conductivity estimated by Maxwell-Eucken's model. The coefficient of thermal expansion of the composite falls in the upper line of Kerner's model, indicating strong bonding between the AlN particle and the Al matrix in the composite.