Microstructural Evolution of Dy₂O₃-TiO₂ Powder Mixtures during Ball Milling and Post-Milled Annealing

The microstructural evolution of Dy₂O₃-TiO₂ powder mixtures during ball milling and post-milled annealing was investigated using XRD, SEM, TEM, and DSC. At high ball-milling rotation speeds, the mixtures were fined, homogenized, nanocrystallized, and later completely amorphized, and the transformation of Dy₂O₃ from the cubic to the monoclinic crystal structure was observed. The amorphous transformation resulted from monoclinic Dy₂O₃, not from cubic Dy₂O₃. However, at low ball-milling rotation speeds, the mixtures were only fined and homogenized. An intermediate phase with a similar crystal structure to that of cubic Dy₂TiO₅ was detected in the amorphous mixtures annealed from 800 to 1000 °C, which was a metastable phase that transformed to orthorhombic Dy₂TiO₅ when the annealing temperature was above 1050 °C. However, at the same annealing temperatures, pyrochlore Dy₂Ti₂O₇ initially formed and subsequently reacted with the remaining Dy₂O₃ to form orthorhombic Dy₂TiO₅ in the homogenous mixtures. The evolutionary mechanism of powder mixtures during ball milling and subsequent annealing was analyzed.