A novel high-Cr CoNi-based superalloy with superior high-temperature microstructural stability, oxidation resistance and mechanical properties

A novel multi-component high-Cr CoNi-based superalloy with superior comprehensive performance was developed and its high-temperature microstructural stability, oxidation resistance and mechanical properties were evaluated mainly by cast polycrystalline alloy. The results indicated that the morphology of γ' phase remained stable and the coarsening rate was slow during the long-term aging at 900~1000°C. The activation energy for γ′ precipitate coarsening of alloy 9CoNi-Cr is determined to be 402 ± 51 kJ/mol, which is higher compared to CMSX-4 and some other Ni-based and Co-based superalloys. Importantly, there was no indication of the formation of Topologically Close-Packed phases during this process. All these demonstrate superior microstructural stability of the alloy. The mass gain of alloy 9CoNi-Cr is 0.6 mg/cm2 after oxidation at 1000°C for 100 h and the oxidation resistance is comparable to advanced Ni-based superalloys CMSX-4, which attributed to the formation of a continuous Al2O3 protective layer. Furthermore, the compressive yield strength of this cast polycrystalline alloy at high temperature is obviously higher than that of conventional Ni-based cast superalloy, and the compressive minimum creep rate at 950°C is comparable to that of conventional Ni-based cast superalloy, showing good mechanical properties of the alloy at high temperature. This is partially due to the high Cr is beneficial on improving the γ and γ' phase strength of alloy 9CoNi-Cr.