The Al 2 O 3 -ZrO 2 -Y 2 O 3 system was studied in the range of necessary condition is satisfaction of Van-Rein's rule: the lowest figurative point for the liquid composition in such a section temperatures 1600-2800؇C by methods of X-ray analysis at must be a saddle point on the liquidus surface of the ternary 20؇C, petrography, DTA in He at temperatures to 2500؇C, system, or a maximum point on the solidus surface. 24 thermal analysis in air using a solar furnace at temperaSince the regions of two-phase equilibria YA ϩ F and tures to 3000؇C, and electron microprobe X-ray analysis.Y 2 A ϩ F are narrow (the composition of F varies within the The stable and metastable phase diagrams were conlimits 4-5 mol%), it may be assumed that partially quasi-binary structed. The liquidus and solidus projections, crystallizasections pass through their centers. The two-phase region tion paths for the alloys, and polythermal sections are Y 3 A 5 ϩ F, as mentioned above, is quite broad (the F composipresented in the article. The structure of the restricting tion lies in the range 18.5-37.0 mol% Y 2 O 3 ). Hence the location systems defines the phase equilibria in the ternary system.of the partially quasi-binary section Y 3 A 5 -F requires a more No ternary compounds were found. The metastable phase precise definition. relations were caused by the ambivalent behavior of Y 3 Al 5 O 12 during crystallization. II. Methods of Investigation I. IntroductionPowders of alumina (99.9%; Donetskij zawod khimreaktiviv, Donetsk), zirconia (99.99%; Donetskij zawod khimreaktiviv, T HE Al 2 O 3 -ZrO 2 -Y 2 O 3 system is one of the basic systems in Donetsk), and yttria (99.99%; Doslidnij zawod Phisiko-khim, the science of ceramics. The phase diagram of this system Institutu AN Ukrajini, Odesa) were used as raw materials. The is necessary for the successful construction of materials.specimens were prepared at 5 mol% intervals by blending in an The phase diagrams of the bounding binary systems have agate mortar with ethanol, and pressed into pellets 5 mm in been examined in some detail. 1-18 The Al 2 O 3 -ZrO 2 system is of diameter and 5 mm in height. For the study of concentration the eutectic type. The ZrO 2 -Y 2 O 3 system is one with limited dependence of the solidus temperature of two-phase alloys mutual solubility of the components in the solid state over Y 3 A 5 ϩ F the specimens were prepared in steps of 1 mol%. 1400ЊC. The Al 2 O 3 -Y 2 O 3 system includes three congruently Thermal treatment was carried out in a DTA device in a helium melted compounds: Y 3 Al 5 O 12 (Y 3 A 5 ), YAlO 3 (YA), and environment to 2500ЊC. 25 Molybdenum was used as the mate-Y 4 Al 2 O 9 (Y 2 A). They are present in a wide temperature range rial for the melting pots. In order to realize metastable condiwithout homogeneity regions. However, the phase transformations the melts were overheated to 50-100ЊC above the liquidus tions of ZrO 2 and Y 2 O 3 are absent in the known phase diagrams temperature and crystallized with a speed not less than 5ЊC/min. of the systems ...

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The phase diagram of the Al2O3–ZrO2–Sm2O3 system was constructed in the temperature range 1250°–2800°C. The phase transformations in the system are completed in eutectic reactions. No ternary compounds or regions of appreciable solid solution were found in the components or binaries in this ternary system. Two new ternary and one new binary eutectics were found. The minimum melting temperature is 1680°C and it corresponds to the ternary eutectic Al2O3+F‐ZrO2+SmAlO3. The solidus surface projection, the schematic of the alloy crystallization path, and the vertical sections present the complete phase diagram of the Al2O3–ZrO2–Sm2O3 system.