Transformation Toughening in Sol–Gel‐Derived Alumina‐Zirconia Composites

Abstract

The microstructures of α‐Al 2 O 3 seeded sol–gel‐derived alumina‐zirconia composites containing 20 wt% unstabilized zirconia (processed from zirconium n‐propoxide) were very fine, with submicrometer alumina grains and small, mainly intergranular zirconia particles, the latter having a critical size for the tetragonal‐to‐monoclinic phase transformation of 0.45 μm. The corresponding ratios of the toughening contribution to the matrix toughness are relatively low (δK c /K 0 <1). This finding is confirmed by an analysis of the tetragonal zirconia particle size dependence of the stress‐induced transformation toughening.