Research has been undertaken to develop new yttria slurry systems for use in mould face coats for investment casting TiAl alloy, solving the pre-gelation problems of commercial yttria slurry systems to increase slurry life. Meanwhile, the new face coats should also have excellent sintering properties, chemical inertness, surface finish and be easy to prepare.ududThe processes of developing the new slurry started with the filler powder investigation by adding different sintering additives into the yttria powder to achieve good sintering properties. Then the best filler powder candidates were selected to make the slurry. Finally, the new face coat slurries were used to make the shell face coat and the chemical inertness of those shells were investigated through the sessile drop and investment casting. In the research, the filler powder and face coat sintering properties were quantified through density, dilatometer testing, X-ray diffraction (XRD) and microstructural change at different testing temperatures. The interaction of different face coat systems and the metal were identified using hardness tests, sessile drop contact angle and the microstructural change at the metal/shell interface.ududIn this research, three water-based binder face coat systems containing YF(_3), Y(_2)O(_3)+0.5wt% Al(_2)O(_3)+ 0.5 wt% ZrO(_2) (YAZ), and B(_2)O(_3) additives were found to have similar or even better sintering properties compared to a commercial face coat. Meanwhile, they had long life.ud
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