Zirconia-related phases in the zirconia/titanium diffusion couple after annealing at 1100°-1550°C

A diffusion couple of 3 mol% Y₂O₃-ZrO₂ and titanium was isothermally annealed in argon at temperatures between 1100° and 1550°C. The phases and microstructure in the ceramic side were investigated using scanning electron microscopy and transmission electron microscopy, both attached to an energy-dispersive spectrometer. After annealing at 1100°C/6 h, zirconia grains did not grow conspicuously and evolved only traces of oxygen, resulting in t-ZrO_2-x but α-Zr. At temperatures above 1300°C, a significant amount of oxygen evolved from zirconia, reducing the O/Zr ratio, such that α-Zr was excluded from t-ZrO_2-x during cooling, yielding a higher O/Zr ratio (≈ 2). When held at 1550°C/6 h, zirconia grains grew rapidly. The α-Zr was segregated on grain boundaries during cooling by the exsolution of zirconium from ZrO_2-x, while twinned t′-ZrO_2-x or lenticular t-ZrO_2-x, which was embedded in ordered c-ZrO_2-x, was found. The ordered c-ZrO_2-x was identified by the 1/5 {113} superlattice reflections of its electron diffraction patterns.