Characterization of the as-cast microstructure and selected properties of the X-40 Co-based superalloy produced via lost-wax casting

The X-40 Co-based superalloy is often used in the aerospace industry directly in as-cast condition and its analysis in this state is essential to understand further possible phase transformations during service. With this in mind, this work focuses on characterizing the material’s as-cast microstructure, phase transformation temperatures and oxidation resistance. Observations and analyses were performed via thermodynamic simulations, X-ray diffraction (XRD), light microscopy (LM), scanning electron microscopy (SEM), scanning-transmission electron microscopy (STEM-HAADF), energy-dispersive X-ray spectroscopy (EDX), dilatometry (DIL) and differential scanning calorimetry (DSC). The microstructure of the dendritic regions consisted of the α matrix, with MC, M 7 C 3 and M 23 C 6 carbides being present in the interdendritic spaces. Based on DIL, it was found that precipitation of the Cr-rich carbides from the saturated α matrix may occur in the range 650–750 °C. DSC determined the incipient melting and liquidus temperatures of the X-40 superalloy during heating to be 1405 °C and 1421 °C, respectively. Based on oxidation resistance tests carried out at 860 °C, it was found that the mass gain after 500 h exposure was 3 times higher in the air than in steam.