Intermediate temperature embrittlement (ITE) is very common in Ni and Ni–Co based superalloys, which seriously restricts the application of these alloys. In this work, we developed a new Ni–Co based superalloy by increasing the content of Cr to eliminate ITE. The superalloy has a yield strength of ∼950 MPa in the intermediate temperature range (600–780 °C), while also maintain a tensile elongation of ∼15 %. Microstructural investigations showed that in the temperature range of 600–780 °C, the microstructure of the alloy consists of nano-sized L12 phase (γ′) distributing inside the γ matrix, and the deformation is dominated by anti-phase boundary (APB) shearing γ′ precipitates, which makes the yield strength of the alloy decrease only slightly at 600–780 °C (compared to that tested at room temperature). More importantly, the element Cr is enriched along the grain boundaries (GBs) to form a protective layer without the formation of brittle topologically close-packed (TCP) phases due to the inverse two-stage aging design. In addition, the formation of a discontinuous precipitation (DP) zone at the GBs can act as a stress buffer and introduce GB serrations to withstand intergranular cracking.
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