Mesostructure of WHIPOX all oxide CMCs

Wound highly porous oxide matrix (WHIPOX) ceramic matrix composites consist of oxide fibers (mullite- or alumina-type) which are embedded in mullite- or alumina-rich matrices, respectively. In the ideal case the fiber distribution is homogeneous; in reality, however, fabrication (winding)-induced matrix agglomerations do occur. As knowledge on the homogeneity of the material is crucial for the prediction of the mechanical behavior a technique to describe the mesostructure of WHIPOX quantitatively has been developed by means of optical microscopy (transmitted light). The technique makes use of light conductivity and opacity of fibers and matrix, respectively. Three-dimensional plots of the matrix agglomerations were obtained by tomographic methods using approximate to 25 individual slices of 1.5 mm thickness for each sample. Samples from different sites of a WHIPOX plate, and samples which have been differently pressed prior to sintering were examined mesostructurally. The study showed that delamination-induced failure of WHIPOX is essentially controlled by localized interlaminate matrix agglomerations. Compression of WHIPOX plates in the pre-sintering moist stage helps to achieve a better homogeneity and thus improved shear strength of WHIPOX components. (C) 2003 Elsevier Science Ltd. All rights reserved.