Abstract
Although the properties of Y2O3-ZrO2 alloys have been extensively investigated for high strength ceramics, solid electrolyte and so on, the phase diagram of this alloy system in the temperature range over 1600°C (1873 K) has not been determined experimentally. In the present paper, the phase diagram of yttria partially stabilized zirconia (Y-PSZ) is proposed. The shapes of cubic-tetragonal (c-t) phase boundaries are like those in the diagrams of Co-Cu and several iron-base binary alloy systems in which Curie-point lines intersect miscibility gaps. The reason can be explained in the considerations that the c-t transition for pure ZrO2 is para-ferroelastic type and that the lattice parameter of t-ZrO2 changes with Y2O3 content continuously to that of c-ZrO2.
Then the formation mechanisms of complex microstructures of Y-PSZ, for examples, {100} type ferro-elastic domain, spinodally decomposed {111} type modulated structure, lath- or lenticular-tetragonal martensite and herring-bone structure, are discussed by using presumed free energy-composition curves.
