Interpenetrating graphite/aluminium (C/Al) composites were produced by pressure infiltration of aluminium-silicon alloys into isotropic microporous graphite preforms. These composites can be defined as multiphase materials in which each phase is threedimensionally interconnected throughout the microstructure, allowing multifunctional characteristics. Due to their specific properties, light metal infiltrated graphites are attractive for lightweight components such as parts of internal combustion engines. Thereby, the low coefficient of thermal expansion and the temperature resistance of carbon materials, in addition to the low density, bestow significant advantages compared to conventional monolithic Al alloys. Optical and transmission electron micrographs show that the metallic phase is strongly modified by the high amount of graphite and by the pore size distribution of the preform. By selecting suitable infiltration temperatures and by ensuring a short contact time between graphite and aluminium in the indirect squeeze casting process, the formation of hygroscopic aluminium carbide can be avoided. The light metal infiltration significantly increases the flexural strength of the composites, compared to porous graphite preforms. As can be shown by theoretical considerations, the significant increase in fracture toughness due to small additions of a ductile metal phase can be attributed to crack bridging by plastic deformation of the ductile aluminium phase in the composite. The analytical consideration of a crack bridging model also reasonably explains the observation that the flexural strength and fracture toughness of these C/Al composites do not decrease at 300°C. The light metal infiltration leads to a significant increase in electrical and thermal conductivity, respectively. Due to the fact that the CTE of graphite preforms is three to six times lower than the CTE of monolithic Al alloys, thermal fatigue may have a negative effect on composite properties. The large mismatch in CTE between graphite and aluminium leads to the building-up of high stress levels in the composites during the cooling after infiltration. These stresses relax at least partially in succeeding thermal treatment. This stress relaxation is observed in the form of a hysteresis in dilatometer measurements. It is worth mentioning that stress relaxation is accompanied by dimensional instability of the composites during the first few thermal cycles (length increase). It is shown that interpenetrating C/Al composites can be susceptible to thermal fatigue, depending on the corresponding monolithic phase properties and on their specific topology. The mechanical properties can be affected by thermal loading, depending on the infiltrated aluminium alloy. On the one hand, the decrease in fracture toughness and accordingly in strength due to thermal cycling (TC) is mainly attributed to aging. Precipitation reactions and silicon phase coarsening during thermal cycling are the most obvious effects. On the other hand, local debonding along the C/Al interface and/or damage evolution within the metallic network lead to a deterioration of physical properties. Synchrotron based X-ray microtomography has shown that the main reason for a decrease in electrical conductivity due to thermal cycling may be attributed to void formation in the highly conductive metal phase. The 3-D microstructural information obtained by X-ray tomographic microscopy is also used for the development of largescale 3-D finite element models after segmentation of the X-ray microtomography images. It is shown that the numerical predictions very accurately reproduce the experimentally-determined electrical conductivity of interpenetrating C/Al composites.weiterlesen