Subsolidus Phase Equilibria and Ordering in the System ZrO2‐Y2O3

Abstract

The subsolidus phase relations in the entire system ZrO2‐Y2O3 were established using DTA, expansion measurements, and room‐ and high‐temperature X‐ray diffraction. Three eutectoid reactions were found in the system: (a) tetragonal zirconia solid solution→monoclinic zirconia solid solution+cubic zirconia solid solution at 4.5 mol% Y2O3 and ∼490°C, (b) cubic zirconia solid solutiow→δ‐phase Y4Zr3O12+hexagonalphase Y6ZrO11 at 45 mol% Y2O3 and ∼1325°±25°C, and (c) yttria C‐type solid solution→wcubic zirconia solid solution+ hexagonal phase Y6ZrO11 at ∼72 mol% Y2O3 and 1650°±50°C. Two ordered phases were also found in the system, one at 40 mol% Y2O3 with ideal formula Y4Zr3O12, and another, a new hexagonal phase, at 75 mol% Y2O3 with formula Y6ZrO11. They decompose at 1375° and >1750°C into cubic zirconia solid solution and yttria C‐type solid solution, respectively. The extent of the cubic zirconia and yttria C‐type solid solution fields was also redetermined. By incorporating the known tetragonal‐cubic zirconia transition temperature and the liquidus temperatures in the system, a new tentative phase diagram is given for the system ZrO2‐Y2O3.