Effects of radiation coatings on directional solidification microstructure of hollow turbine blades

To obtain a turbine blade with refined directional crystals, the effects of the graphite coating and the chromium oxide coating on the directional solidification microstructure are studied by numerical simulations and experiments. Numerical simulation results show that the temperature gradient at the top castings is improved by increasing the emissivity of the mold surface. The experimental results show that after the mold surface is coated with the chromium oxide, the heat dissipation performance of the mold surface is remarkably improved, and the primary dendrite spacing at the top of the casting is reduced. The average primary dendrite spacing at the top of the casting is 336 μm, 12.5% less than the one without coating and 2.9% lower than the one coated with graphite, and the directional solidification microstructure is significantly refined. A turbine blade with refined directional crystal is formed by using the integral ceramic mold with the chromium oxide coating.