Abstract
This work uses room temperature X-ray diffraction and electron microscopy to investigate the effect of CO 2 laser treatments (800–2000 W, 10–15 s) on phase transformations and microstructural modification of sintered (1600 °C, 4 h) disks, A x Z y C z (where A, Z and C denote Al 2O 3, ZrO 2 and CeO 2 respectively, and the subscripts represent molar ratios). Laser treatments under these conditions caused melting and more or less sublimation of all the samples; subsequent solidification and condension (predominant for CeO 2-rich composition) resulted in different microstructures between the samples. Dendritic and cellular domain structures due both to eutectic growth of α-Al 2O 3 and ZrO 2-CeO 2 solid solution were found in specimens A 30C 63C 7 and A 70Z 27C 3 respectively. In the CeO 2-rich specimen A 40Z 12C 48 a drastic effect of condensation caused dendritic clusters of CeO 2 cubes (fluorite structure with minor amount of ZrO 2 and Al 2O 3 in solid solution) which overlaid on an Al 2O 3-rich matrix, predominantly CeAlO 3. Condensation through a rapidly solidifying liquid caused incorporation of Al 2O 3 in the fluorite structure and hence deviation from the octahedral shape predicted by the periodic bond chain model. Solute (Al 2O 3) trapping also suppressed the martensitic transformation of tetragonal (t-) to monoclinic (m-) ZrO 2 as manifested by the dendritic t-ZrO 2 cooled from the Al 2O 3-ZrO 2 eutectic. Laser treatment increased the Ce 2+ Ce 4+ ratio and hence darkened the samples.
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