Hiromichi Takebe1, Tsuneya Okano1, Takuya Semba2 and Kenji Morinaga3
1Graduate Student, Kyushu University, Kasuga, Fukuoka
The tetragonal to monoclinic transformation in Y-TZP specimens and mullite/Y-TZP composites containing 5 vol% mullite, which progresses from surface to interior by annealing at 373 K in boiling water, was investigated by scanning acoustic microscope (SAM). The Rayleigh wave velocity, VR, which was measured on surfaces of the specimens, was lowered by the transformation. We obtained relationships between the transformation depth which was converted from the VR and annealing time. The depth after the annealing for 612.0 ks in the Y-TZP specimens was 7.2 μm, while in the mullite/Y-TZP composites it was less than 1.0 μm. Apparently the relationships suggested that a nucleation-growth stage existed in the process of the transformation. The transformation mechanism was discussed from changes of the transformation depth and SAM image contrast with the annealing time.
monoclinic, tetragonal, yttria-doped tetragonal zirconia polycrystals, transformation, acoustic microscope, water vapor, transformation depth
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