Mechanically Induced Zone Darkening of Alumina/Ceria-Stabrlized Zirconia Composites |
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| Authors: | Valter Sergo Chiara Schmid Sergio Meriani Anthony G. Evans |
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| Affiliation: | Dipartimento di Ingegneria dei Materiali e Chimica Applicata, Universitàdegli Studi di Trieste, Trieste, Italy;Materials Department, University of California, Santa Barbara, California 93107 |
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| Abstract: | Alumina/ceria-stabilized zirconia bars tested in four-point bending exhibited deformation bands on the tensile side due to localized tetragonal-to-monoclinic transformation. These bands became increasingly darker and were fully visible some weeks after the bending experiment. XPS spectra revealed that the darker regions are characterized by a higher concentration of cerium in the + 3 oxidation state, as opposed to other undeformed regions, in which + 4 is the predominant oxidation state. A numerical calculation established that residual stresses exist in the deformation bands. It is suggested that these stresses facilitate the reduction of cerium with the gradient in stress motivating the diffusion of oxygen vacancies. |
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