TRANSMISSION ELECTRON-MICROSCOPY STUDY OF ZIRCONIA-ALUMINA NANOLAMINATES GROWN BY REACTIVE SPUTTER-DEPOSITION - PART II - TRANSFORMATION BEHAVIOR OF TETRAGONAL ZIRCONIA NANOCRYSTALLITES

Zirconia-alumina multilayer films consisting of polycrystalline tetrag onal zirconia and amorphous alumina were grown by reactive sputter dep osition to study the transformation behavior of tetragonal zirconia na nocrystallites during in-situ electron beam irradiation and cooling ex periments in a transmission electron microscope. It was found that the constraint provided by the alumina layers in the nanolaminate was imp ortant in the stabilization of the tetragonal phase of the zirconia du ring irradiation and cooling, and overrides the thermodynamic predicti on based on an unconstrained crystallite model which governs the phase composition of zirconia crystallites during growth. A partial transfo rmation of the tetragonal zirconia crystallites to the monoclinic phas e was observed in cases where the alumina constraint is greatly relaxe d due to knock-on damage to the alumina layers by the electron beam of the microscope. In extreme cases of alumina loss, re-crystallization of the zirconia occurred producing larger monoclinic zirconia crystall ites. Fundamentally, the nano-sized zirconia crystallites present in t he films under investigation were found to have a different transforma tion behavior compared to micron-sized dopant-stabilized tetragonal zi rconia crystallites. (C) 1998 Elsevier Science S.A. All rights reserve d.