INDENTATION STUDIES ON Y2O3-STABILIZED ZRO2 .2. TOUGHNESS DETERMINATION FROM STABLE GROWTH OF INDENTATION-INDUCED CRACKS

Stable indentation cracks were grown in four-point bend tests to study the fracture toughness of two Y2O3-stabilized ZrO2 ceramics containing 3 and 4 mol% Y2O3. By combining microscopic in situ stable crack growth observations at discrete stresses with crack profile measurements, the dependence of toughness on crack extension was determined from crack extension plots, which graphically separate the crack driving residual stress intensity and applied stress intensity factors. Both materials exhibit steeply rising R-curves, with a plateau toughness of 4.5 and 3.1 MPa.m1/2 for the 3- and 4-mol% materials, respectively. The magnitude of the plateau toughness reflects the fraction of tetragonal grains contributing to transformation toughening.