Influence of Alumina on the Structure and Mechanical Properties of Yttria Stabilized Zirconia Composites.

Composite structure of yttria 4.5 wt stabilized zirconia YSZ with added Al2O3 0.3-7.5 wt have been investigated. They show fracture toughness KIc and strength MOR values in excess of 9.0 MPa X the square root of M and 500 MPa respectively more than twice that normally reported for YSZ samples of like composition. Starting materials used were floated Al2O3 and precipitated YSZ powders approx. 99.9 purity of average partical size 0.03 micrometers. The powders were washed, dispersed, ball milled, spray dried, dry pressed and the resultant compacts sintered at 1300 C8 h. Microstructures obtained were of uniform grain size 0.2-0.4 micrometers with discrete Al2O3 inclusions, approximately the same size as the YSZ grains, dispersed throughout the composite structure. The strengthening mechanism involved dissipation of strain energy by plastic deformation of the Al2O3 inclusions in the YSZ matrix. Variation in the mechanical properties and structure of the composite as a function of added Al2O3 was correlated with DC conductivity, X-ray diffraction and lattice parameter data. The X-ray data showed splitting of the main peaks indicating a primarily tetragonal phase. Lattice parameter changes with increasing Al2O3 were attributed to direct substitution of Al3 for Zr4 ions at low Al2O3 0.325 wt content resulting in increased oxygen vacancies, higher conductivity and lower activation energy.