Compactness and Corrosion Resistance of BaZrO3 Composite Mould for Directional Solidification of TiAl Alloy

Chemical reaction of different degrees can occur for TiAl alloys with traditional refractory materials due to the high activity of TiAl alloys, which restricts their application in directional solidification castings. In this paper, the BaZrO3 composite mould was prepared by self-synthesized BaZrO3 powder as the surface layer (yttrium sol as a binder), Al2O3 as a back layer (silica sol as a binder). The influence of BaZrO3 particle size on the compactness of the mould, the morphology of penetration layer after directional solidification of the alloy, and the contaminant content in the alloy were investigated. The evolution of the microstructure of the surface layer and porosity, the interaction between the mould and the alloy, the morphology and composition of the interface, and the contaminant content of the alloy were investigated by an optical microscope (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction analysis (XRD), Archimedes' principle, Inductively Coupled Plasma (ICP) and Nitrogen and oxygen analyzer (IGI, LECO TC-436). The results show that the surface of the mould using fine-grained particles as the coating is denser and smoother after sintering at high temperature, the number of pores between particles is reduced and the size decreases, the porosity of the surface layer decreases from 17.3% to 13.5%. The surface layer thickness of the optimized mould is from 1000 mu m (2 layers) to 3000 mu m (4 layers). The thickness of the adhesive layer between the BaZrO3 surface layer and the Al2O3 back layer is increased from 300 to 1200 mu m, and the adhesion is also enhanced. The interface penetration layer between the optimized mould and alloy is reduced from 900 to 300 mu m, the penetration of the alloy melt is limited within the surface layer, and no exudate is observed in the back layer. The content of Ba, Zr, O in the alloy are reduced from 89, 16800, 7580 to 28, 4760, 3690 mu g/g.