Modeling and Fabrication of Fine‐Grain Alumina‐Zirconia Composites Produced from Nanocrystalline Precursors

Abstract

Fully dense fine‐grained 32.6‐vol%‐zirconia‐toughened alumina composites have been fabricated from nanocrystalline rapidly solidified material. A model considering the thermodynamics of the constrained t‐ZrO2m‐ZrO2 phase transformation was developed for this percolated two‐phase material. This analysis indicated that the grain size at which this phase transformation is thermodynamically favorable was 1.26 µm in a composite that contained 32.6 vol% ZrO2 and was stabilized with 1.50 mol% Y2O3. These results of the model compared favorably with experimental results, showing that grains of this size could be retained after heating to temperatures of as high as 1600°C. The rapidly solidified precursor was ball‐milled into submicrometer powder and centrifugally cast into green specimens that were pressureless sintered to full density at temperatures as low as 1500°C. A composite containing nearly 100%t‐ZrO2 was produced by pressureless sintering at 1500°C and a composite containing 45 vol%t‐ZrO2/55 vol%m‐ZrO2 was obtained by sintering at 1600°C. The resulting two‐phase microstructures contained uniformly distributed, micrometer‐size grains whose sizes are consistent with the facilitation of transformation and microcrack toughening.