  The low temperature autoclave aging behavior of zirconia toughened alumina
composites processed by a classical powder mixing processing route was analyzed
using atomic force microscopy (AFM), scanning electron microscopy and X-Ray
diffraction. The transformation was evaluated in terms of nucleation and
growth, assessed by XRD. The time-temperature equivalency of the transformation
was used to measure an apparent activation energy of the nucleation stage of
the transformation of 78kJ/mol. The microstructural features influencing the
transformation were identified, and the influence of the alumina matrix on the
transformation was investigated. Transformation progression grain by grain was
observed by AFM. Transformation does not only occur in zirconia agglomerates
but also in isolated zirconia grains. The matrix could partially inhibit the
transformation. This behavior could be rationalized considering the
constraining effect of the alumina matrix, shape strain accommodation arguments
and microstructural homogeneity effects.
