Pressureless Sintering t-zirconia@d-Al2O3 (54 mol%) Core–Shell Nanopowders at 11201C Provides Dense t-Zirconia-Toughened a-Al2O3 Nanocomposites

Zirconia-toughened alumina (ZTA) is of growing importance in a wide variety of fields exemplified by ZTA prosthetic implants. Unfortunately, ZTA composites are generally difficult to process because of the need to preserve the tetragonal zirconia phase in the final dense ceramic, coincident with the need to fully densify the a-Al2O3 component. We report here that liquid-feed flame spray pyrolysis of mixtures of metalloorganic precursors of alumina and zirconia at varying compositional ratios provide access in one step to core–shell nanoparticles, wherein the shell is d-Al2O3 and the core is a perfect single crystal of tetragonal (t-) zirconia. Pressureless sintering studies provided parameters whereby these nanopowder compacts could be sintered to full density (499%) at temperatures just above 11001C converting the shell component to a-Al2O3 but preserving the t-ZrO2 without the need for any dopants. The final average grain sizes of these sintered compacts are r200 nm. The resulting materials exhibit the expected response to mechanical deformation with the subsequent production of monoclinic ZrO2. These materials appear to offer a low-temperature, low-cost route to fine-grained ZTA with varied Al2O3:t-ZrO2 compositions.