Preparation Of Ceramic Shell Mold Used In Nb-silicide Based Alloy And Its Interface Reaction With Nb-silicide Based Alloy

Nb-Si based alloy have great potential for high temperature structure components serving at1200-1400℃with higher melting point(above1750℃), low density, and high temperature strength. Therefore, it is important to prepare investment casting ceramic shell mold used in Nb-Si based alloy. The research studied the influence of raw materials and the preparing process on the performance of ceramic shell mold. And the interface reaction between the alloy and the ceramic shell mold has been studied in this paper.In choosing binder systems, the ceramic shell molds prepared by silica sol and Zirconium acetate represented better performance than the ceramic shell molds prepared by Ammonium zirconium carbonate and Yttrium oxide sol.In the drying process, the drying time of the ceramic shell molds prepared by ZrO2powder and Ammonium zirconium carbonate was shorter than the ceramic shell molds prepared by ZrO2powder and Yttrium oxide sol. Therefore, the production efficiency of the former is higher. The ceramic shell molds had the best comprehensive performance when the sintering temperature was1550℃, and the keeping time was4h.The rheological property of slurries and the properties of ceramic shell molds was the best when the size distribution of ZrO2powder was "double-peak":the compactness of the face coating of the ceramic shell molds was the best, the bending strength of the ceramic shell molds could reach up to5.06MPa, and the viscosity of the ceramic shell molds lowed to29.1%. With the decreasing of the powder/sol ratio, the viscosity of the slurries decreased, the compactness of the face coat of the ceramic shell molds decreased, and the strength of the ceramic shell molds decreased, but the viscosity of the ceramic shell molds and the gravitational distortion of ceramic shell molds increased.The interface reaction results between Nb-Si alloy and the ceramic shell prepared by ZrO2powder and Yttrium oxide sol showed that:the interface reaction was not observed at the metal-mold interface from the experiment at1900℃; However, a continuous reaction layer with the thickness from200μm to325μm was found at the metal-mold interface after reaction experiment at2000℃. The alloying elements diffused from the Nb-Si based alloy molten to the face coating of the ceramic shell mold, which is the unidirectional diffusion phenomenon. In the interface reaction, Hf aggregated at the metal-mold interface to form oxides through high temperature chemical reaction with the ceramic shell mold. The interface reaction showed that the ceramic shell molds prepared by ZrO2powder and Yttrium oxide sol could be used in investment casting process of Nb-Si based alloy.