Achieving Excellent Strength–Ductility in Nb-Si Superalloys via Stable Bi-Phases Structure and Nano-Precipitation Behaviors

Nb-Si-based superalloys are considered as the most potential candidate materials for nickel-based superalloys due to the lower density and higher using temperature. Here, a type of stable Nbss/γNb₅Si₃ bi-phases structure with a coherent interface has been successfully designed. Additionally, the Nbss and γNb₅Si₃ phases showcase the orientation relationship of [1 0 0]_Nb// (Formula presented.) and (0 1 1)_Nb// (Formula presented.). There are also some nano-γNb₅Si₃ phases in the Nbss matrix with a coherent relationship. The lower mixing enthalpies of Ti, Zr, Hf, and Si in Nbss phases accelerate the formation of nano-γNb₅Si₃, and the dislocations as crystal defects provide the heterogeneous nucleation sites for nano-γNb₅Si₃ phases. In addition, the room temperature fracture toughness has been improved to 15.03 MPa·m^1/2, resulting from the intrinsic toughness of Nbss and γNb₅Si₃ phases being improved according to nanoindentation. Moreover, the nanoindentation experiment exhibits that the optimal values of microhardness and elastic modulus are 5.53 and 160.31 GPa for Nbss, and 13.88 and 218.26 GPa for γ(Nb, X)₅Si₃ phases, respectively. Under high temperature conditions, the phase boundaries of brittle γ(Nb, X)₅Si₃ are deformable at 1200°C, which can accommodate more plasticity. In addition, the recrystallized behaviors are also found in our alloys, which can consume lots of dislocations to relieve the stress concentration.