Transformation Plasticity and Toughening in CeO2-Partially-Stabilized Zirconia–Alumina (Ce-TZP/Al2O3) Composites Doped with MnO

Microstructure, phase stability, and mechanical properties of CeO₂-partially-stabilized zirconia (12 mol% Ce-TZP) containing 10 wt% Al₂O₃ and 1.5 wt% MnO were studied in relation to the base Ce-TZP and the Ce-TZP/Al₂O₃ composite without MnO. The MnO reacted with both CeO₂ and Al₂O₃ to form a new phase of approximate composition CeMnAl₁₁O₁₉. The reacted phase had a magnetoplumbite structure and formed elongated, needlelike crystals. The MnO-doped Ce-TZP/Al₂O₃ composites sintered at an optimum temperature of 1550°C exhibited high strength (650 MPa in four-point bending) and rising crack-growth-resistance behavior, with fracture toughness increasing from 7.6 to 10.3 MPa.In¹² in compact tension tests. These improved mechanical properties were associated with relatively high tetragonal-to-monoclinic transformation temperature ( M _s=−42°C) at small grain size (2.5 μm), significant transformation plasticity in mechanical tests (bending, uniaxial tension, and uniaxial compression) and transformation zones at crack tips in compact tension specimens. The transformation yield stress, zone size, and fracture toughness were sensitive to the sintering temperature varied in the range 1500° to 1600°C. Analysis of the transformation zones using Raman microprobe spectroscopy and calculation of zone shielding for the observed zones indicated that a large fraction of the fracture toughness (∼70%) was derived from transformation toughening.