Surface Displacement Analysis of the Transformed Zone in Magnesia Partially Stabilized Zirconia

The utility of surface displacement measurements as a source of quantitative information about subsurface plastic deformation is illustrated by analysis of the transformed zone in magnesia partially stabilized zirconia (Mg-PSZ). The surface displacements are derived from partial fringe analysis of optical interference micrographs. Their interpretation is based on analytical and numerical calculations of the surface displacements generated by a transforming semi-ellipsoidal in-homogeneity at the surface of a half-space. Inhomogeneous transformed zones, i.e., those possessing nonuniform distributions of transformation strain, are modeled as linear sums of nested, uniformly transforming semi-ellipsoids. It is found that the transformed zones around either through cracks or small, surface-breaking cracks in Mg-PSZ are indeed inhomogeneous. The degree of transformation is near the maximum possible only within a few microns of the crack plane. It falls away linearly or faster as the distance from the crack plane increases. Qualitative evidence suggests furthermore that significant net shear transformation persists near the crack plane. These conclusions are consistent with phase analysis using Raman spectroscopy.