Consequences of partial {Hf by Ta}-Substitution on the high temperature properties of a HfC-Reinforced Ni-based superalloy

Hafnium carbides have recently demonstrated high interest to strengthen equi-axed polycrystalline superalloys. Notably chromia-forming Ni-based alloys reinforced by HfC appeared as being both oxidation-resistant and creep-resistant at temperatures higher than 1000 degrees C. Since high contents in Hf are required for achieving such high performances, it can be interesting to investigate possibilities of partial replacement of this expensive and rather rare element by tantalum. In this work two levels of partial substitution were tested. Two alloys were fabricated by foundry and subjected to creep and oxidation tests at 1100 degrees C. Despite the presence of Ta instead a part of Hf, the strengthening carbide network is exclusively - at least principally - composed of MC carbides which demonstrated good stability at 1100 degrees C. The creep resistance stays very good, only few lower than the high performance HfC-reinforced reference alloy. The isothermal oxidation and resistance against oxide scale spallation at cooling are as good as the ones earlier observed for the reference alloy. This shows that the two alloys - which are cheaper than the remarkable HfC-reinforced reference alloy - are capable of good creep-resistance and very good oxidation behavior at this particularly high temperature for superalloys not protected by thermal barrier coating.