THE TRANSFORMATION STRUCTURE OF ZIRCONIA-ALUMINA NANOLAMINATES STUDIED BY HIGH-RESOLUTION ELECTRON-MICROSCOPY

Quantitative high resolution electron microscopy (HREM) was employed t o study the crystallography of a zirconia-alumina transformation-tough ening nanolaminate. The nanolaminate consisted of alternating layers o f polycrystalline zirconia and amorphous alumina. The zirconia layer t hickness was scaled to insure unity volume fraction of the metastable tetragonal phase at the growth temperature, as predicted by an end-poi nt thermodynamics model and verified by x-ray diffraction. In the micr oscopy sample, phase identification was achieved from precise measurem ents of lattice spacings using digital diffractograms of individual na nocrystallites. Of the nanocrystallites analyzed, (22+/-6)% were monoc linic in a distinct crystallographic relationship with their tetragona l neighbors. The following plane and direction relationships were iden tified: m(100)//t(100) and m[001]//t[001]. The observed structure is t he result of a stress-induced transformation from the tetragonal phase . This transformation was localized to nanosized regions within the in dividual zirconia layers. (C) 1996 American Institute of Physics.