Some high temperature properties of novel Al–containing TaC–reinforced cast nickel–based alloys

The aim of the present work is to start exploring the high temperature (H.T.) behaviours of nickel alloys reinforced by carbides but containing aluminium instead chromium to be chemically resistant. Two alloys designed to be TaC–strengthened and alumina – forming were elaborated and studied in terms of as-cast microstructures, refractoriness, creep resistance and oxidation at H.T. Both alloys present high melting start temperatures, allowing testing them at 1200°C. They are double–phased and the single carbide present is TaC, of an eutectic nature and located in the interdendritic spaces. Their creep resistances, evaluated in 3 points bending mode, are of interest, taking into account the elevated test temperature (1200°C) and their mass gains by oxidation at 1200°C are slow, with kinetics much slower than chroma–forming alloys with the same tantalum and carbon contents. However, none of them is really alumina–forming as shown by the complexity of the oxide scales. Furthermore, the two alloys suffer from severe oxide spallation during cooling, despite the moderate cooling rates applied here. Future evolutions may consists in increasing the Al contents and introducing elements favouring a better adherence of the oxide scales, e.g. yttrium.