Pressureless Sintering t ‐zirconia@δ‐Al ₂ O ₃ (54 mol%) Core–Shell Nanopowders at 1120°C Provides Dense t ‐Zirconia‐Toughened α‐Al ₂ O ₃ 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 α‐Al 2 O 3 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 δ‐Al 2 O 3 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 (>99%) at temperatures just above 1100°C converting the shell component to α‐Al 2 O 3 but preserving the t ‐ZrO 2 without the need for any dopants. The final average grain sizes of these sintered compacts are ≤200 nm. The resulting materials exhibit the expected response to mechanical deformation with the subsequent production of monoclinic ZrO 2 . These materials appear to offer a low‐temperature, low‐cost route to fine‐grained ZTA with varied Al 2 O 3 : t ‐ZrO 2 compositions.