Investigation of the interactions between titanium and calcium zirconium oxide (CaZrO3) ceramics modified with alumina

Abstract

Powdered mixtures of CaO, ZrO 2 and Al 2 O 3 in various ratios were hot pressed. The mixtures reacted with titanium at 1600°C for 30 min in argon to evaluate the suitable ceramic crucibles for casting of titanium. The interfacial microstructures between titanium and ceramic composites were characterized using X-ray diffractometer, scanning and transmission electron microscope. The produced hot pressed mixtures that were chemically bonded together, contained calcium aluminate (CaAl 2 O 4 ), calcium dialuminate (CaAl 4 O 7 ), cubic zirconia (c-ZrO 2 ), and calcium zirconium oxide (CaZrO 3 ). The increase in Al 2 O 3 amount led to the decrease in CaZrO 3 amount and an increase in the amount of CaAl 2 O 4 , CaAl 4 O 7 and c-ZrO 2 due to the reaction of CaO and Al 2 O 3 . At the end of the reaction of the ceramic mixtures with Ti at 1600°C for 30 min, the acicular α-Ti and β ′ -Ti were formed at the interface of Ti and the composites containing up to 10 vol.% Al 2 O 3 . In composites containing more than 20 vol.% Al 2 O 3 , Ti 3 Al 5 was found at the interface instead of α-Ti and β ′ -Ti. Furthermore, CaZrO 3 , ZrO 2 and Ca 3 Al 2 O 6 existed on the sides of the ceramic far away from the interface. CaZrO 3 /Al 2 O 3 composites with less than 20 vol.% Al 2 O 3 could be a potential crucible or mould material for productive applications in titanium casting.

Microstructural evolution and interfacial reactions between Ti and ZrO2/CaTiO3 composites

“…However, Figure 6C reveals that needle‐like α‐Ti appeared near the interface of the Ti/CZ sample. The dark needle‐like regions are the α‐Ti phase and the bright regions are the β'‐Ti phase, and these findings are consistent with the results of Lin and Lin 12,15,19 . The needle‐like α‐Ti phase and the β'‐Ti phase typically appeared on the Ti side of the micrograph because of the interfacial reactions between Ti and 3YZrO 2 .…”

“…A large amount of Ti from the Ti side diffused into the region occupied by ZrO 2 and CaZrO 3 and formed acicular α‐Ti, β'‐Ti, and residual CaZrO 3 . Furthermore, the precipitation of the needle‐like α‐Ti(Zr,O) solid solution on the β'‐Ti(Zr,O) substrate during the cooling process was evident at the Ti and ZrO 2 interface 15,19 …”

“…The dark needle-like regions are the α-Ti phase and the bright regions are the β'-Ti phase, and these findings are consistent with the results of Lin and Lin. 12,15,19 The needle-like α-Ti phase and the β'-Ti phase typically appeared on the Ti side of the micrograph because of the interfacial reactions between Ti and 3YZrO 2 . The reaction layer thickness of ceramic side near the interface of Ti/3Z7CT, Ti/5Z5CT, and Ti/CZ was evaluated as 125, 80 and 100 μm, respectively.…”

“…Recently, ternary ceramic composites, such as CaO–ZrO 2 –Al 2 O 3 , have been investigated for Ti casting at temperatures as high as 1600°C 19 . Introducing Ti in CaO–ZrO 2 –Al 2 O 3 composites with Al 2 O 3 more than 20 vol.% prevented the formation of α‐case (α‐Ti or β‐Ti) and generated a CaZrO 3 layer at the interface, which blocked the mutual diffusion of O and Zr.…”

“…17,18 When a 5 mol% CaO-ZrO 2 composite reacted with Ti at 1550°C/6 h, a TiO reaction layer, which functioned as a blocking layer, formed at the interface. 15 Furthermore, Lin et al 19 prepared CaZrO 3 powder by hot pressing a mixture of ZrO 2 and CaO, which exhibited an excellent inhibitory effect on the interface by forming a CaZrO 3 reaction layer on the Ti side, effectively blocking the mutual diffusion of Ti and O. However, residual ZrO 2 does not completely react with CaO and results in the formation of α-case at the interface.…”