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 ‐ZrO 2 m ‐ZrO 2 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% ZrO 2 and was stabilized with 1.50 mol% Y 2 O 3 . 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 ‐ZrO 2 was produced by pressureless sintering at 1500°C and a composite containing 45 vol% t ‐ZrO 2 /55 vol% m ‐ZrO 2 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.