3-dimensional microstructure characterization of porous ceramic matrix composites by X-ray tomography and FIB-slicing as database for numerical modelling

Abstract

All-oxide ceramic composites (CMC) are developed for applications in combustion chambers of gas turbines as an alternative for metallic materials aiming at reduction of fuel consumption and NOx emission. At DLR a CMC is processed by winding an endless alumina fibre bundle, which is infiltrated by aqueous alumina slurry, on a mandrel and further sintering of the generated ceramic ‘green body’. The result is a CMC with complex hierarchical microstructure, which is controlled by the processing parameters. Fibre arrangement, fibre volume fraction, and matrix porosity can be varied in a wide range. For determining the effect of the complex microstructure on the resulting mechanical properties, numerical models are typically based on microstructural parameters derived from microscopic analyses of cross sections. A challenge is deriving correct 3-dimensional geometry data for the numerical model from such 2-dimensional images. A distinct improvement is provided by non-destructive X-ray tomography on the length scale from mm to µm and by combined sequential focused ion beam (FIB) ablation and scanning electron microscopy, which allows for construction of 3-dimensional microstructure features in the submicron range.