New insights into the microstructural stability based on the element segregation behavior at γ/γ′ interface in Ni-based single crystal superalloys with Ru addition

A new insight into the microstructural stability was proposed in Ni-based single crystal superalloys with Ru addition, and the element segregation behavior at γ/γ′ interface was investigated by three-dimensional atom probe technology (3D-APT). After standard heat treatment, it was found that Ru addition barely altered the element partitioning coefficient between γ matrix and γ′ phase, and no element-segregation layer was observed at γ/γ′ interface. During the heat exposure at 1100 °C, Ru addition obviously promoted the rafting of the γ′ precipitates and inhibited the precipitation of topological close-packed (TCP) phases. It was more important that an element-segregation layer containing Re, Co, and Cr was formed in the γ matrix close to the γ/γ′ interface due to an "uphill diffusion" effect, and its concentration was obviously reduced after Ru addition. Finally, the microstructural stability based on the element segregation behavior at γ/γ′ interface was discussed. This element-segregation layer increased the γ/γ′ interfacial energy by increasing the absolute value of the lattice misfit of γ/γ′ interface to promote the rafting of the γ′ precipitates after Ru addition. On the other hand, the decrease of the segregation concentration of Re, Co, and Cr elements as TCP phase-forming elements near the γ/γ′ interface due to a "reverse partitioning" effect inhibits the precipitation of TCP phases in Ni-based single crystal superalloys after Ru addition.