Behaviour in oxidation at 1200°C of two nickel-based alloys reinforced by (Ta, Hf)C carbides

Unlike gamma/gamma prime nickel-based single crystals, some carbide-strengthened polycrystalline superalloys can be efficiently helped by their reinforcing particles to resist creep deformation at temperatures above 1100 degrees C. Various MC carbides in high quantity demonstrated recently such potential interest. Among them, HfC monocarbides are remarkable for their morphological resistance to heat, thus by their strengthening effect in the long term. Unfortunately, more wt-% of the expensive Hf elements may cause problems. In this work, two limited replacements of Hf, by Ta in a Ni-Cr alloy, are envisaged for a base of 6 wt-% M (M = Hf + Ta). Their resistance to microstructure changes and their oxidation properties is investigated at 1200 degrees C. The results show that, after 50 h at 1200 degrees C, microstructures have been evolved a little more than an HfC-reinforced Ni-based superalloys studied earlier. In contrast, the oxidation behaviours stayed good, except for the resistance against oxide spallation at cooling if the Ta content becomes higher (between 2 and 4 wt-%) than the Hf content. The optimal value of Ta will be found in future work.