Phase diagrams of the systems Al 2O 3–ZrO 2–Ln(Y) 2O 3 as a source of multiphase eutectics for creating composite structural and functional materials

Abstract

Phase equilibria in the ternary systems Al 2O 3–ZrO 2–Ln 2O 3 (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 ZrO 2 in the binary bounding system Al 2O 3–ZrO 2. 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 La 2O 3 system to 1840 °C for the Lu 2O 3 system. Fluorite-type phases equilibrate with garnet-type phases for the systems from Tb 2O 3 to Lu 2O 3. In the systems from Pr 2O 3 to Gd 2O 3 they equilibrate with perovskite-type phases and β-Al 2O 3. 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.