Effect of Y content on interface reaction and wettability between a nickel-base single crystal superalloy melt and ceramic mould

In this paper, the effect of Y content on interface reaction and wettability between a nickel-base single crystal supperalloy melt and ceramic mould were studied by means of sessile drop tests. The microstructural characterization of the alloy-ceramic interface and the elemental compositions of reaction products were performed by scanning electron microscope (SEM) and electron probe micro-analyzer (EPMA), the phases of reaction products were identified by X-ray diffraction (XRD), and the surface analysis of reaction products was carried out by X-ray photoelectron spectroscopy (XPS). The results showed that Al and Hf in the alloy reacted with SiO2 in the ceramic mould when Y content was lower than 0.011 wt%, and the reaction products were Al2O3 and HfO2, with little change in the wetting angle. However, when Y content was higher than 0.017 wt%, Y and Al in the alloy reacted with SiO2 in the ceramic mould, and the wetting angle decreased significantly. 0.017 wt% was the critical concentration of Y content that would cause interface reactions. The reaction products of 0.017 and 0.025 wt% Y alloys were Y3Al2(AlO4)(3), the reaction products of 0.1 wt% Y alloy were Y3Al5O12 and Y4Al2O9, and the reaction products of 0.5 and 1.0 wt% Y alloys were double reaction layer composed of Y2O3 and Y3Al5O12. Si generated by the interface reactions could react with O-2 in the atmosphere to form SiOx during the cooling of the alloy-ceramic couples. (C) 2019 Published by Elsevier B.V.