Effect of Carbides on Interfacial Reactions Between Superalloy DZ40M and Ceramic Mold in Directional Solidification

Abstract

During the directional solidification (DS) of superalloys, the active alloy elements react with the ceramic mold, deteriorating the surface quality and affecting the dimensional accuracy of the alloys. It is important to investigate the interfacial reactions between the alloy melt and ceramic mold and to investigate the effect of the interfacial reactions on the structures of the alloy. Superalloy DZ40M was prepared by DS technology, the microstructures and element distributions of the alloy and the alloy-ceramic interface were observed by a scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS), and the interfacial reactions were analyzed from a thermodynamic perspective. Carbides are important strengthening phases in the alloy. Interfacial reactions between the carbides and the ceramic mold were further investigated. The results show that the alloy structure mainly contains Co (Cr/Ni/Zr/Al/W/Ti) solid solution columnar crystals (Co_ss), nearly continuously distributed Cr-enriched M₇C₃-type carbides as well as Ti/Zr/W-enriched MC-type carbides skeletal precipitates. The reactions between the Co_ss and the ceramic mold were mild, with a reaction layer of about 20–40 μm thickness, while the reaction between the grain boundary precipitates and the ceramic mold was severe because of a high content of Cr in the M₇C₃-type carbides and the presence of active elements Ti and Zr in the MC-type carbides, with a reaction layer of about 50 μm thickness. In addition, almost no obvious penetration of the mold refractory was observed in the interior of the alloy, showing that the ceramic mold has a relatively stable performance in investment casting of superalloy DZ40M.