Effects of Annealing Temperature on Microstructural Development at the Interface Between Zirconia and Titanium

Abstract

The interfacial reaction layers in the Ti/ZrO2 diffusion couples, isothermally annealed in argon at temperatures ranging from 1100° to 1550°C for 6 h, were characterized using scanning electron microscopy and transmission electron microscopy, both attached with an energy‐dispersive spectrometer. Very limited reaction occurred between Ti and ZrO2 at 1100°C. A β′‐Ti(Zr, O) layer and a two‐phase α‐Ti(O)+β′‐Ti(Zr, O) layer were found in the titanium side after annealing at T≥1300°C and T≥1400°C, respectively. A three‐phase layer, consisting of Ti2ZrO+α‐Ti(O, Zr)+β′‐Ti (O, Zr), was formed after annealing at 1550°C. In the zirconia side near the original interface, β′‐Ti coexisted with fine spherical c‐ZrO2−x, which dissolved a significant amount of Y2O3 in solid solution at T≥1300°C. Further into the ceramic side, the α‐Zr was formed due to the exsolution of Zr out of the metastable ZrO2−x after annealing at T≥1300°C: the α‐Zr was very fine and dense at 1300°C, continuously distributed along grain boundaries at 1400°C, and became coarsened at 1550°C. Zirconia grains grew significantly at T≥1400°C, with the lenticular t‐ZrO2−x being precipitated in c‐ZrO2−x. Finally, the microstructural development and diffusion paths in the Ti/ZrO2 diffusion couples annealed at various temperatures were also described with the aid of the Ti–Zr–O ternary phase diagram.