| Aluminosilicate glass matrix composites containing non-sintering inclusions of beta silicon nitride whiskers, ranging from 0 to 21 v/o, were fabricated by tape casting. The tape cast greensheets were stacked, laminated, and subsequently sintered to evaluate the densification behavior of the composites as a function of whisker loading.;Right cylinder greensheet pellet samples for dilatometry studies were fabricated in two orientations, such that the greensheets were aligned perpendicular to, and parallel to the cylinder axis. Samples were laminated at varying pressures to achieve equivalent "matrix densities", and were sintered at 800;Sintering studies showed that, for a given matrix density, strain rate decreased with increasing whisker additions. It was determined, from electron microscopy and x-ray diffraction analysis, that the whiskers were oriented with their long axes in the plane of the greensheets. This orientation effect resulted in anisotropic densification rates parallel to (x), and perpendicular to (z) the greensheet (i.e., whisker) plane. It was demonstrated that, for a given whisker loading, the axial strain rate was slower in the plane of the whiskers than perpendicular to the whisker plane (i.e., ;The experimental data were fitted to a sintering model which predicts that the sintering rates in the x and z directions vary nearly in proportion to the viscosities. The independently measured uniaxial viscosities were used in the model, and it was shown that the strain rates predicted by the model were within a factor of two of the experimentally determined strain rates as a function of matrix density, for a given whisker loading.;The inhibiting effect on the densification rate, due to the presence of whiskers, was found to exceed the predictions of earlier models which apply to composites with spherical inclusions. This is related to the fact that, for a given volume fraction of inclusions, the frequency of matrix-inclusion contacts is much higher when small whiskers are present than when large, spherical inclusions are present. The matrix particle packing in a composite containing large inclusions more closely resembles the packing in the matrix glass alone, whereas the matrix particle packing in a composite containing small whisker inclusions is different from that of the matrix alone. |
