Fabrication of double-ceramic-layer TBCs by suspension plasma spray

Rare-earth zirconates, such as La2Zr2O7 and Gd2Zr2O7, have been investigated as one of the candidates for replacing conventional yttria-stabilized zirconia (YSZ) for thermal barrier coating (TBC) applications at higher turbine inlet temperatures. Rare-earth zirconate oxides exhibit little phase transformation upon heating up to melting temperature as well as low thermal conductivity, where as their mechanical properties is inferior to those of YSZ TBCs. Double-ceramic-layer (DCL) TBCs have been investigated in order to take advantage of beneficial characteristics of both YSZ and rare-earth zirconate. In this study, the fabrication of DCL-TBCs with YSZ layer and rare-earth-zirconate top layer by using suspension plasma spray are reported. Microstructure, compositional profile, thermal conductivity, and thermal durability of DCL-TBCs are characterized. The usefulness of these DCL-TBCs is also discussed

Formation of Al2O3-HfO2 Eutectic EBC Film on Silicon Carbide Substrate

The formation mechanism of Al2O3-HfO2 eutectic structure, the preparation method, and the formation mechanism of the eutectic EBC layer on the silicon carbide substrate are summarized. Al2O3-HfO2 eutectic EBC film is prepared by optical zone melting method on the silicon carbide substrate. At high temperature, a small amount of silicon carbide decomposed into silicon and carbon. The components of Al2O3 and HfO2 in molten phase also react with the free carbon. The Al2O3 phase reacts with free carbon and vapor species of AlO phase is formed. The composition of the molten phase becomes HfO2 rich from the eutectic composition. HfO2 phase also reacts with the free carbon and HfC phase is formed on the silicon carbide substrate; then a high density intermediate layer is formed. The adhesion between the intermediate layer and the substrate is excellent by an anchor effect. When the solidification process finished before all of HfO2 phase is reduced to HfC phase, HfC-HfO2 functionally graded layer is formed on the silicon carbide substrate and the Al2O3-HfO2 eutectic structure grows from the top of the intermediate layer

Non-uniform Sintering Behavior of Y_2O_3 Ceramics

The densification of Y_2O_3 was carried out by spark plasma sintering (SPS) technique with various heating rates (5, 10, 20, and 50°C/min) and holding times (2, 5, 20, and 60 mins) at 1000°C. Among the entire specimens, uniform or non-uniform sintering behavior was divided based on the heating rate of 20°C/min like Fig. 1. At the heating rate of 20°C/min, the center was totally translucent and densified, and the boundary of the specimen was opaque. On increasing the holding time, the center became opaque and the periphery became translucent. It is special result that the sintering is conducted thoroughly and the regions were divided. As a result of the microstructural analysis, the grain size in the center of all specimens was larger than the periphery. Especially, at the high heating rate (20 and 50°C/min), the difference in grain size between the center and periphery was significantly increased around 3.5 times on average. In addition, there was a difference of the pore size and distribution. Above non-uniform sintering behavior could be explained by setting the assumption (the mass transfer occurred from center to periphery). The densification was carried out with lots of defects in sintered bodies and coarsening was significantly induced in the center due to the assumption and the dynamic grain growth on increasing the heating rate [1]. The evidence to demonstrate the assumption will be obtained by additional experiments

Fabrication of dense ZrO2/CNT composites: Influence of Bead-milling treatment

Highly concentrated zirconia-carbon nanotube (CNT) water suspensions were prepared using an advanced milling technique. The bead-milling operation parameters were optimized for this system and used to prepare zirconia-stabilized water-based suspensions with different CNT contents. The effects of different milling conditions were studied. The particle dispersion was evaluated by SEM observations on dried suspension. Green’s density and SEM observations of compacts were used to follow the colloidal dispersability of the composites. Materials of tetragonal zirconia and CNTs were prepared with a high concentration of CNTs (1, 5, and 10 wt pct CNT). The homogeneous dispersion and distribution of the fibers in the bulk material after slip casting of the suspension were examined. The samples were sintered using spark plasma sintering (SPS) at 1473 K (1200 °C) and finally, fully dense materials were obtained. The mechanical properties were evaluated using the Vickers indentation technique.Fil: Suarez, Gustavo. Provincia de Buenos Aires. Gobernación. Comision de Invest.científicas. Centro de Tecnología de Recursos Minerales y Ceramica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - la Plata. Centro de Tecnología de Recursos Minerales y Ceramica; ArgentinaFil: Jang, Byung Koog. Tsukuba University. National Institute For Materials Science; JapónFil: Aglietti, Esteban Fausto. Provincia de Buenos Aires. Gobernación. Comision de Invest.científicas. Centro de Tecnología de Recursos Minerales y Ceramica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - la Plata. Centro de Tecnología de Recursos Minerales y Ceramica; ArgentinaFil: Sakka, Yoshio. Tsukuba University. National Institute For Materials Science; Japó