MICROSTRUCTURAL CHARACTERIZATION OF ZRO2 O'-SIALON COMPOSITES/

Zirconia has demonstrated a very moderate toughening effect in nitroge n-based ceramic composites because the reaction between tetragonal zir conia (t-ZrO2) and nitrogen results in additional zirconia stabilizati on to a nontransformable t' or cubic structure. In O'-SiAION matrices, the oxygen concentration increases and the oxygen-rich intergranular glassy phase prevents zirconia from nitridation, As a result, tetragon al ZrO2 is maintained and is transformable in the O'-SiAION materials, The present study has provided transmission electron microscopy (TEM) evidence of the zirconia transformation and the associated toughening effect in a ZrO2/O'-SiAION composite. The implications and limitation s of the transformation on toughening of the material are discussed.