The interfacial reactions between ceramic moulds and DZ417G and DZ125 superalloys were investigated. The microstructure and composition of the interface region were observed by optical microscope, X-ray diffraction and scanning electron microscope with energy dispersive spectroscopy. The results showed that (Al1-xCrx)2O3solid solution phase with pink color was formed from the dissolution of Cr2O3and Al2O3and vapour phase, which was transferred to the reaction surfaces. The reaction layer thicknesses of DZ417G and DZ125 alloys were about in the range of 40-50μm. The interface reaction product between DZ417G alloy and ceramic mould was TiO2and the product between DZ125 alloy and ceramic mould was HfO2.

In this study, mullite was used as the addition to prepare silicon based ceramic cores, and the effect of mullite content on the mechanical and chemical properties was investigated. The phase composition and the morphology of the ceramic cores were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) respectively. The results indicated that the shrinkage was induced by the addition of mullite and contaminations. The intensity of pre-heated cristobalite increased sharply with the mullite content increasing, which could improve the high temperature deformation simultaneously. However, mullite was difficult to remove by reacting with KOH which decreased the leaching rate of ceramic core. When mullite content was 15 wt%, the shrinkage of ceramic core was 0.78%, the creep at 1540 °C for 1 h was 0.3 mm and the leaching rate was 0.1 g/min, which meets the need of ceramic core of hollow turbine blades.

In this work, the effects of the bimodal particle size distribution of fused silica on the properties of silica-based ceramic cores have been investigated. In order to simulate a casting process condition, the core specimens were sintered at 1220°C, tested at above 1500°C. Three point bending tests were carried out on all the prepared specimens. Phase evolution and microstructure were investigated by XRD and SEM respectively. The results showed that with the bimodal granularity distribution broaden and the content of coarse particles increasing, the contraction, flexural strength and creep deformation of ceramic cores decreased linearly, as the content of mineralizer was determined. Coarse particles served as the skeleton to relieve the contraction in ceramic matrix and avoided sharp decrease of flexural strength. The high temperature properties were largely determined by the combined effects of crystallization and skeleton network. The crystallization depended mostly on the fine particles, and the skeleton network was prerequisite to avoid creep deformation.

In this study, cristobalite was used as the addition to prepare silica based ceramic cores, and then the effect of cristobalite content on the mechanical and chemical properties was investigated. The increasing of pre-added cristobalite content resulted in more crystallized cristobalite in the sintered samples and the variation of the linear shrinkage and mechanical properties. When pre-added cristobalite content was 6.0 wt%, the shrinkage of ceramic core was 0.42%, the creep at 1540°C for 30 min was 0.10 mm, and the flexural strength at room temperature and at 1550°C were 25.2 MPa and 28.7 MPa, respectively, which meets the need of ceramic cores of hollow turbine blades.

A new technique for the fabrication of yttria stabilized zirconia (YSZ) substrates using aqueous gel-casting has been developed. This technique has been used to fabricate planar thin-substrate YSZ fuel cells. A thin-substrate YSZ electrolyte with high density and low porosity was prepared by this method with 57vol% solid content slurry. The character of the technique was discussed based on the influence of dispersant and pH value on slurry. After sintering, the YSZ electrolyte thickness is between 100 and 200µm, and the electrolyte area is 100 × 100 mm2. The research shows that aqueous gel-casting allows fabricate thin YSZ substrate with high density and homogenous structure. The method is suitable for preparing thin-substrate electrolyte of yttria stabilized zirconia.