Effect of BN on Sintering Property and Titanium Melt Erosion Resistance of AlN Refractories

AlN/BN refractory composite ceramics, which is oxygen-free and easy to process, were prepared by pressure-free sintering at 1850 degrees C for 4 h with a new type of refractory material AlN as the matrix, adding different contents of high-activity h-BN and sintering assistant Y2O3. The microstructure of the composite ceramics was analyzed, and the wetting behavior and interfacial reaction between the composite ceramic and TiAl melt were studied. The results show that the addition of BN particles can effectively fill the gap of AlN particles and promote the sintering densification of composite ceramics. When adding 5wt% BN particles, the density of the composite ceramics reaches the highest of 89.24%. The microstructure of the composite ceramics is composed of AlN, BN and yttrium aluminate Y4Al2O9 that is mainly distributed at the interface of AlN particles. The interfacial wettability between the composite ceramics and the TiAl melt is reduced by addition of BN particles. The interfacial wettability angle of the composite ceramic containing 5wt% BN and the TiAl melt is about 136 degrees, indicating that the composite ceramics and TiAl melt are poorly wetted and the composite ceramics exhibit good chemical inertia. The interfacial reaction experiments show that the composite ceramics have good corrosion resistance to TiAl melt. The interface between the composite ceramics and TiAl melt is smooth and clear, the thickness of the interfacial layer is only 9.5 mu m, and no obvious element diffusion occurs. It indicates that AlN/BN composite ceramics are a potential refractory for titanium alloy melting.