Interface formation in infiltrated Al(Si)/diamond composites

This study pertains to the investigation of interface formation in infiltrated Al-based composites with high-volume fractions of monocrystalline synthetic diamond particles. The interface characteristics are discussed with respect to process conditions and Al matrix chemistry. To this end, two infiltration techniques, i.e., squeeze-casting and gas pressure infiltration are compared and the effect of Si-addition to the Al matrix is addressed. Eventually, thermal properties of the composite materials are presented and are in turn related to the interface characteristics. Electron microscopy investigations reveal a distinct 50-200-nm-thick layer at the interface between the metal matrix and the diamond particle, regardless of process history and matrix chemistry. This layer is amorphous and consists of carbon, aluminium and oxygen. Additionally, nanocrystallites of Al2OC and enrichment of Si are observed within this interface layer in the Si-free, squeeze-casted material and in the gas pressure-infiltrated material with 7 wt.% of Si, respectively. Despite the fact that no evidence of SiC is found in the Si-containing composites, the process conditions experienced in gas pressure infiltration are clearly more favourable than those experienced in squeeze casting with respect to interfacial bonding and thermal properties. Actually, between 25 and 50 degrees C, the gas pressure-infiltrated AlSi/diamond composite yields a thermal conductivity of 375 W/m K along with a coefficient of thermal expansion of 7 x 10(-6)/K. (c) 2005 Elsevier B.V. All rights reserved.