Compositional Dependence of Phase Formation Mechanisms at the Interface Between Titanium and Calcia‐Stabilized Zirconia at 1550°C

ZrO 2 samples with various CaO contents were fabricated by hot pressing, whereby CaO was dissolved by and/or reacted with ZrO 2 to form a solid solution and/or CaZr 4 O 9 , respectively. After a reaction with Ti at 1550°C for 6 h in argon, the interfacial microstructures were characterized using X‐ray diffraction and analytical electron microscopy. Experimental results were very different from those found previously in the Y 2 O 3 –ZrO 2 system. The 5 mol% CaO–ZrO 2 sample was relatively stable due to the formation of a thin TiO layer acting as a diffusion barrier phase. However, α‐Ti(O), β′‐Ti (Zr, O), and/or Ti 2 ZrO were found in 9 or 17 mol% CaO–ZrO 2 due to extensive interdiffusion of Ti, O, and Zr with a much thinner (β′‐Ti+α‐Ti) layer in 17 mol% CaO–ZrO 2 than in 9 mol% CaO–ZrO 2 . Because CaO was hardly dissolved into Ti, it fully remained in the residual ZrO 2 , leading to the formation of spherical CaZrO 3 in 9 mol% CaO–ZrO 2 and columnar CaZrO 3 in 17 mol% CaO–ZrO 2 . In the region far from the original interface, abundant intergranular α‐Zr was formed in 5 or 9 mol% CaO–ZrO 2 . Scattered α‐Zr and CaZrO 3 were found in 17 mol% CaO–ZrO 2 because a high concentration of extrinsic oxygen vacancies, which were created by the substitution of Ca +2 for Zr +4 , effectively retarded the reduction of zirconia.