Abstract
Similarities exist between the tetragonal to monoclinic transformation of ZrO2 and the monoclinic (B) to cubic (C) transformation of Dy2O3. On cooling the transformation occurs at 1950°C and is accompanied by an 8 % volume increase which causes shattering of bulk specimens. The transformation can be suppressed, however, by minor additions of CaO. An attempt was made to fabricate a “PSD” analogue to partially stabilized zirconia (PSZ).As-received and chemically precipitated powders of pure Dy2O3 were mixed with CaO (0 to 25 mol%), uniaxially and cold isostatically pressed, sealed in small Mo crucibles and sintered at various temperatures (1900° or 1650°C) and times before cooling or subsequent annealing treatments. Some pellets were annealed in the two phase (B + C) region at 1700°C for 2 hours before quenching. Specimens were examined by XRD, TEM, EDS, HVEM, and STEM.A fast quenching in combination with the =8 mol% CaO additions were found to be essential for retention of the high temperature B phase down to room temperature.
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