Kazuhide Matsumoto

EB-PVD process and thermal properties of hafnia-based thermal barrier coating

Abstract Thermal barrier coatings (TBCs) are being developed for the key technology of gas turbine and diesel engine applications. In general, 8 mass% Y2O3–ZrO2 (8YSZ) coating materials are used as the top coating of TBCs. The development of hafnia-based TBC was started in order to realize the high reliability and durability in comparison with 8YSZ, and the 7.5 mass% Y2O3–HfO2 (7.5YSH) was selected for coating material. By the investigation of electron-beam physical vapor deposition (EB-PVD) process using 7.5YSH ceramic ingot, 7.5YSH top coating with about 200 µm thickness could be formed. The microstructure of the 7.5YSH coated at coating temperature of 850 °C showed columnars of laminated thin crystals. On the other hand, the structure of the 7.5YSH coated at coating temperature of 950 °C showed solid columnars. From the result of sintering behavior obtained by heating test of 7.5YSH coating, it was recognized that the thermal durability of 7.5YSH coating was improved up to about 100 °C in comparison with 8YSZ coating. This tendency was confirmed by the experimental result of the thermal expansion characteristics of sintered 7.5YSH and 8YSZ. ©2003 Elsevier Science Ltd. All rights reserved.

Transmission Electron Microscopy Study of Thermal Barrier Coatings Fabricated by Electron Beam-Physical Vapor Deposition

Yttria stabilized zirconia (YSZ) film was deposited on to a stationary metal substrate by electron beam-physical vapor deposition (EB-PVD) at 850 C ° . The film was characterized using transmission electron microscopy and scanning electron microscopy. The film was composed of inverted triangular-based pyramidal grains (T-grains) and inverted diamond-based pyramidal grains (D-grains). The T-grains were aligned in the <111> direction and D-grains in <110> perpendicularly to the substrate. Furthermore, striated lines of nano-pores, which should be strongly related to the thermal conductivity of the film, were observed in each YSZ grain. The pores were oriented in the <110> in the (111) plane and distributed across { 4 11 } planes in the YSZ grains aligned in the <111> (T-grains). In the YSZ grain aligned in the <110> (D-grains), the pores were oriented in the [ 10 1 ] and the [001] directions in the (110) and distributed across the (001) and ( 10 1 ).