MECHANICALLY INDUCED ZONE DARKENING OF ALUMINA CERIA-STABILIZED ZIRCONIA COMPOSITES/

Alumina/ceria-stabilized zirconia bars tested in four-point bending ex hibited deformation bands on the tensile side due to localized tetrago nal-to-monoclinic transformation. These bands became increasingly dark er and mere fully visible some weeks after the bending experiment. XPS spectra revealed that the darker regions are characterized by a highe r concentration of cerium in the +3 oxidation state, as opposed to oth er undeformed regions, in which +4 is the predominant oxidation state. A numerical calculation established that residual stresses exist in t he deformation bands. It is suggested that these stresses facilitate t he reduction of cerium with the gradient in stress motivating the diff usion of oxygen vacancies.