Phase diagrams of the systems Al2O3–ZrO2–Ln(Y)2O3 as a source of multiphase eutectics for creating composite structural and functional materials

Phase equilibria in the ternary systems Al2O3–ZrO2–Ln2O3 (Ln = La, Nd, Sm, Gd, Er, Yb and Y) were investigated by identical methods in all range of concentrations and 1250–2700 °C temperature range using differential and derivative in solar furnace thermal analysis in controlled medias, X-ray diffraction phase analysis, local X-ray spectral analysis, chemical analysis, electron and optical microscopy, petrography. The phase diagrams of the systems studied are presented as isothermal at 1650 °C sections and melting diagrams. The interaction in the systems is characterized by the absence of ternary compounds and regions of appreciable solid solutions based on the binary compounds and components. Only narrow regions of ternary solid solutions were discovered at high temperatures by CALPHAD method and because of existing small solubility on the base of ZrO2 in the binary bounding system Al2O3–ZrO2. The phase equilibria in the systems are determined by zirconia as the most stable compound. Solidification in the systems is completed in eutectic reactions. The established interaction regularities allowed to forecast interaction and phase diagrams construction in systems with other lanthanides (Ce, Pr, Pm, Eu, Tb, Dy, Ho, Tm, Lu). New 13 quasibinary and 26 ternary eutectics were found for the first time. Their temperatures rise from 1660 °C for the La2O3 system to 1840 °C for the Lu2O3 system. Fluorite-type phases equilibrate with garnet-type phases for the systems from Tb2O3 to Lu2O3. In the systems from Pr2O3 to Gd2O3 they equilibrate with perovskite-type phases and β-Al2O3. On the base of microstructure investigations it was established that three-phase alumina-rich eutectics crystallizes according to the mechanism of cooperative growth. It opens up possibilities to obtain composite materials using directional solidification method.