Study On Ceramic-Superalloy Interface Reactions During The Directional Solidification Processing

The ceramic/superalloy interface, including metal/core and metal/mold, during the directional solidification was investigated. The research provides the foundation for the optimization of ceramic core and mold material.In this thesis, two new chemical compositions alloys were obtained based DD6 alloy, which are 3% Ru and 1% Y contained respectively.Conventional Unisolidification process was implemented during the experiments. The behaviors of interfaces were research between the Re, Ru and Y containing alloys and SiO₂, Al₂O₃-based ceramic core and Al₂O₃-based ceramic mold.The experimental results indicated that DD6 alloy and 3% Ru-containing alloy react with SiO₂ core at the interface and form Al₂O₃ and HfO₂ during directional solidification, whereas the two alloys and Al₂O₃-based core at the interface are stable. 1% Y additions to DD6 alloy result in reacting at the metal/SiO₂ ceramic core interface. Corrosion can be found on the surface of the core. Y and Al elements osmoses and distribute into the entire SiO₂ ceramic core. Herringbone-like TCP phases enriched Si were observed, majority of which precipitate in interdendritic regions and the rest in the dendrite trunk.With the addition of 1% Y to DD6 alloy, there are no significant reacts at the interface between the liquid metal/Al₂O₃-based core/811A ceramic mold each other, which indicate that three parts are stable during directional column and single crystal blade casting process. Whereas metallurgical chemistry reactions have been found at the interface between the liquid metal/SiO₂-based core/811A ceramic mold each other. It was deduced that Al plays an important role in the Si-Y-Al ternary system, which promotes the strongly reaction between Si and Y elements, forming new phase of Si-Y-Al. This low melting point phase deteriorates the service performance of core and mold.