High-temperature mechanical spectroscopy of yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) with different amounts of intergranular phase

Y-TZP ceramics of different grain sizes and with various content of amorpho us intergranular phase have been studied by mechanical spectroscopy and tra nsmission electron microscopy. In all grades both clean grain boundaries an d grain boundaries wetted by an amorphous him are present. In the materials with higher amount of intergranular phase, large amorphous pockets are pre sent. A thermally activated mechanical-loss peak is observed in all grades at 1600 K (0.1 Hz; Delta H-act = 560 +/- 20 kJ/mol). This peak evolves into a background at low frequencies and high temperature. The peak position an d height depend on the grain size; the background is grain-size independent . The peak is interpreted as the limited sliding of those grains that are s eparated by an amorphous film. The background is attributed to the beginnin g of microcreep. In the grades with amorphous pockets an additional peak, i nterpreted as the a-relaxation of these pockets, is observed at 1425 K (0.1 Hz; Delta H-act = 570 +/- 20 kJ/mol). (C) 2000 Acta Metallurgica Inc. Publ ished by Elsevier Science Ltd. All rights reserved.