Transformation Zone Shape, Size, and Crack‐Growth‐Resistance [ R ‐Curve] Behavior of Ceria‐Partially‐Stabilized Zirconia Polycrystals

Transformation zone shape, size, and crack‐growth‐resistance ( R ‐curve) behavior were studied in precracked and annealed single‐edge notch bend specimens of commercial‐grade ceriapartially‐stabilized zirconia polycrystals as a function of applied load. Well‐defined transformation zones with a characteristic elongated shape in the plane of the crack were observed. It is shown that the observed zone shape is significantly different from the shape predicted by a combined shear/dilatation yield criterion and the stress field of the crack prior to the transformation. The length of the transformation zone directly ahead of the crack tip is in better agreement with the prediction of the Dugdale plastic strip zone model. The fracture toughness increment showed the characteristic square root dependence on the transformation zone width, but the magnitude of the toughness increment was not consistent with the predictions of the theoretical models of transformation toughening.