Creep and oxidation kinetics at 1100 °C of nickel-base alloys reinforced by hafnium carbides

Abstract The mechanical reinforcement of polycrystalline alloys at elevated temperature may be achieved by HfC carbides. Generally such alloys must be also resistant against oxidation by hot gases and corrosion by molten substances. Polycrystalline chromium-rich nickel-based alloys represent a good solution for answering these requirements about the high temperature chemical resistance. Unfortunately they tend to be rather mechanically weak at high temperature compared to γ/γ′ single crystals. In this work a new family of alloys, combining a chromium-rich nickel-based matrix and an interdendritic HfC carbide network, is studied. Two equiaxed cast alloys were elaborated by classical foundry and the obtained microstructures were examined. Two types of high temperature properties were characterized at 1100 °C, creep resistance and oxidation kinetic. The microstructures of the two alloys are composed of a dendritic austenitic matrix and of script-like eutectic carbides which are recognized to be very favorable for high strength at high temperature. Creep tests proved this potential benefit by showing that these alloys are much more resistant than usual cast polycrystalline nickel-based alloys. The base made of nickel and the 25 wt.% content in chromium allow obtaining a chromia-forming behavior leading to good resistance against oxidation in hot air.