Effect of AlF3·3H2O addition on microstructure and properties of ceramic shell for investment casting

Using fused corundum powder as raw material， silica sol as a binder， and aluminum fluoride trihydrate as mullite phase conversion promoter， the slurry composition of the ceramic shell for directional solidification molding of turbine blades was designed， and the ceramic shell was prepared. The microstructure and phase composition， high-temperature permeability， thermal expansion， high-temperature mechanics， and resistance to high-temperature deformation of the shell were studied. The results show that after sintering at 1200 ℃， with the help of the catalysis of aluminum fluoride trihydrate， the alumina in the shell reacts with silicon dioxide to produce a mullite whisker. Compared with the ceramic shell without aluminum fluoride trihydrate， the permeability of the shell is increased by about 1 time， the thermal diffusion coefficient is increased， and the thermal expansion coefficient is decreased. At the same time， the addition of aluminum fluoride trihydrate also reduces the high-temperature strength of the shell to a suitable range， improves the high-temperature yield of the shell， and makes the shell maintain a good high-temperature deformation resistance.