Anisotropy in the indentation fracture piezoelectric titanate ceramics.

The mechanical anisotropy of several poled and unpoled well characterised l ead-titanate based piezoelectrics with different tetragonal distortions was studied using indentation techniques, with applied loads both in perpendic ular and parallel orientation to the polarization axis. Values of hardness, H-v, H-k, and Young's Modulus, E, showed no dependance on poling state, an d therefore no anisotropy. However, the indentation fracture toughness, K-I c, was affected by poling, with a significant anisotropy in the poled sampl es, with lower and higher values for crack lengths in the directions parall el and perpendicular to the poling axis. To observe the behavior of the cra cks caused by the indentations the damage profiles below the indented surfa ces were studied for the unpoled and three different orientations of the po led samples. The origin of the observed anisotropy in fracture behavior is thought to be the consequence of a toughening mechanism associated with dom ain switching. However, the effect appears to be exaggerated by anisotropic plastic deformation at the indenter tip and the associated anisotropic str ess field that results.