Combined effects of microvoids and phase contiguity on the thermal expansion of metal-ceramic composites

Numerical modeling of the thermal expansion behavior of metal-ceramic composite materials are presented, with a focus on the combined effects of microvoids and phase contiguity. The analyses are based on a two-dimensional unit-cell model, by recourse to the finite element method. Voids, presumably resulting from incomplete infiltration of metal during processing of the actual composites, are assumed to locate at the concave corners of the ceramic phase in the model systems. Both the composites with a continuous ceramic phase and with a continuous metallic phase are considered. It is found that the overall thermal expansion is strongly influenced by the presence of voids in composites with a continuous ceramic phase. The thermal expansion is relatively insensitive to voids in composites with a continuous metallic phase. These findings can be rationalized by the examination of the evolution of field quantites. Qualitative comparisons with experiments support the numerical results.