Crystal structure and microstructure of metal carbides in Ni superalloy prepared by investment casting

Rene 80, as a representative Ni-based superalloy for producing jet turbine blades, shows superior mechanical properties and microstructure stability during high-temperature engine operation. This study attempts to provide a deep insight into the microstructure of as-cast Rene 80 prepared by the investment casting method. For better understanding of the microstructure, the characterization of the samples was performed using optical microscopy (OM), field emission scanning electron microscopy (FE-SEM), and energy dispersive spectroscopy (EDS) techniques. Microstructural investigation shows that the as-cast microstructure of this alloy consists of a dendritic gamma matrix, an interdendritic gamma/gamma' phase, a gamma' phase, and MC and M23C6 carbides. Because of its high chromium content, the dominant phase was the M23C6-type carbide, whereas other elements in the alloy lead to the MC-type carbide. In this study, the as-cast microstructure was a gamma/gamma' dendritic matrix, with precipitation of a secondary phase, such as the M23C6 carbides, at the grain boundaries and interdendritic zones.