Fabrication of Y2O3 doped BaZrO3 coating on Al2O3 applied to solidification of titanium alloy

The investment casting is one of the most versatile modern technique for metal forming, however, the high chemical stability of ceramic shell materials is required due to the high activity of titanium melt. The Al2O3 is one kind of the common refractory material, which can not be directly used for casting titanium alloys because of its reaction with the melt and contamination caused by this reaction. In this paper, the Y2O3 doped BaZrO3 coating was fabricated on the Al2O3 matrix in order to develop a novel casting and directional solidification technology. Using the Al2O3 as the matrix, the Y2O3 doped BaZrO3 coating was prepared by smearing the slurry, dusting the BaZrO3 powder and sintering them. The reaction between the Al2O3 matrix and the protective coating, the surface quality and chemical stability of the Y2O3 doped BaZrO3 coating were investigated using the optical microscope (OM), energy dispersive spectrometer (EDS) and scanning electronic microscope (SEM), respectively. Afterward, the interaction between Y2O3 doped BaZrO3 coating and titanium melt was discussed. Optical microscope and SEM results showed that the BaZrO3 coating possessed the good surface morphology and high chemical stability, and EDS results showed the thickness of interaction layer between the Al2O3 matrix and the protective coating did not vary with the sintering time and temperature (at 1500 °C and 1600 °C for 2, 4 and 6 h). The thickness of diffusion layer was 10 μm for the rod of Ti-46Al-8Nb with the directional solidification, the same was the counterpart for the casting part of Ti-6Al-4V alloy. This may imply that Y2O3 doped BaZrO3 is a promising coating for the solidification of titanium alloy.