Microstructures and high-temperature strength of gel-casting Al 2 O 3 -based ceramic molds with coated aluminum additive

A method of coating aluminum powder with Nylon-12 via a dissolution-precipitation process to prevent hydrolysis reaction in gel casting was introduced in this study. Aluminum powder additive was adopted to facilitate the synthesis of mullite via Al-SiO2 reaction which could help to improve the high-temperature strength of Al2O3-based ceramic molds. However, the aluminum powder would have hydrolysis reaction and affect the rheological properties of the slurry. While adding the aluminum powder that was treated by corroding oxidation film and coated with Nylon-12, the slurry could finish the gel casting process. The coated aluminum almost had no impact on the rheology property of the slurry, as the viscosities of the slurries with different diameters of coated aluminum additive were all under 1 Pa s. The microstructures and phase compositions of the sintered ceramic samples were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Effects of coated aluminum powder additive on the high-temperature strength of Al2O3-based ceramic containing nano-SiO2 and MgO were investigated. The bending strength of the ceramic mold at 1500 °C peaked at 20.88 MPa with 1 μm coated aluminum powder additive. Finally, a porous Al2O3-based ceramic mold was fabricated with adoption of this method and successfully applied to cast a turbine blade, indicating that the high-temperature strength of the ceramic mold could meet the casting requirements.