On the phase relations in the ZrO2-YO1.5-AlO1.5 system

Experimental studies of samples with the composition 23.5 mol% ZrO2, 59.2 mol% YO1.5 and 17.3 mol% AlO1.5 indicated a change of tie-lines in the temperature range 1523-1613 K due to the invariant reaction YAM + F = YAP + delta as predicted by Calphad method. The thermodynamic description of the ZrO2-YO1.5-AlO1.5 system based on the modelling of fluorite (F) and bixbyite (C) structures as different phases is derived. The isothermal sections at 1523, 1573 and 1623 K are calculated and two invariant solid state reactions are indicated: YAM + F = YAP + delta at 1614 K and F = delta + YAM + C at 1602 K. Ternary interaction parameter in liquid phase is assessed to get an improved fit of experimental data on liquidus surface. The calculated liquidus surface is in a good agreement with experimental data. Reasonable agreement with experimental data on isoplethal sections is obtained. The T-0-lines for fluorite double left right arrow tetragonal and tetragonal double left right arrow monoclinic transformations are calculated in the ZrO2-YO1.5-AlO1.5 system. (c) 2005 Elsevier B.V. All rights reserved.