Comparative study of porosity in 3Y-TZP superplastic ceramics by ultra-small-angle neutron scattering and scanning electron microscopy image analysis

Recent measurements of cavitation in superplastically strained 3Y-TZP ceramics by scanning electron microscopy and ultra small-angle neutron scattering (USANS) led to systematic differences in volume fractions of cavities determined by both methods. We show that the scattering curves measured by double crystal USANS diffractometers can be calculated directly from scanning electron micrographs taken from a single section of the material, without any assumptions of cavity shape or distribution. This technique was used to compare the USANS measurements with electron micrographs and showed that the calculated and measured curves agree well for medium scattering vectors. This result confirms that the electron micrographs represent well the microstructure of small cavities up to about 0.6 μm in radius. On the contrary, the calculations resulted in systematically larger intensities for small scattering vectors. This indicates that large cavities are responsible for the observed differences in volume fraction for the samples with nominal strain above 100%. An explanation by an inhomogeneous distribution of large cavities generated at high strains in the bulk of the tensile specimen and/or by surface artifacts is suggested.