In-situ synthesis of dispersed borides induced high-performance brazed DD5 superalloy via a novel sandwich-structured interlayer

Abstract

The aggregation of boron into continuous brittle phases during the brazing of single-crystal superalloys remains a critical challenge for fabricating aero-engines turbine components. Herein, in-situ synthesis of dispersed borides was achieved using a novel sandwich-structured interlayer (SS-interlayer) of NiCrSiB/NiCrWMoAlRe/NiCrSiB. The liquid NiCrSiB interlayer eliminated the initial interface gaps via its excellent wettability, thereby facilitating interdiffusion of B, Al and Ta atoms and inducing precipitation of a lot of γ' nanoparticles. The SS-interlayer, used for brazing at 1100 °C for 20 min, enabled a 74.4% enhancement in shear strength to 753.2 MPa compared to a conventional single-component joint. The ultimate tensile strength of the SS-joint was 791.5 MPa at room temperature and decreased to 601.3 MPa at 850°C. The polycrystalline NiCrWMoAlRe layer functioned as an effective boron getter, with its abundant grain boundaries providing favorable sites for boride nucleation. This led to the initial precipitation of borides at grain boundaries, followed by their subsequent formation within the γ channels, resulting in a dispersed boride zone (DBZ) embedded in an equiaxed polycrystalline γ+γ′ matrix. The dispersed borides formed semi-coherent interfaces with the matrix, as characterized by specific orientation relationships such as [1 @#x0305;00]M3B2//[310]FCC and (002 @#x0305;) M3B2//(002 @#x0305;) FCC, which promoted uniform strain partitioning and inhibited the formation of a continuous brittle eutectic. The formation of a residual zone (RZ) in the SS-joint, characterized by a single-crystal/polycrystalline (S/P) interface and coarse Ni₂₃B₆ and M₃B₂-type borides, constituted its primary weak region. The phases within the RZ exhibited semi-coherent orientation relationships: [001 @#x0305;] M₃B₂//[110] Ni₂₃B₆, [001 @#x0305;] M₃B₂//[110] γ, [110] Ni₂₃B₆//[110] γ, corresponding to lattice mismatches of 15.3%, 7.3%, and 5.2%. The fracture mode transformed from brittle cleavage to a ductile-brittle mixed mode with numerous dimples. This strategy provides a viable pathway for high-performance brazed single-crystal joints.