Designing stable Nbss/γNb₅Si₃ structure promote the strength-ductility for Nb-Si based superalloys

Nb-Si based superalloys are one of the most promising candidate materials for the new generation aeroengines because of their high operating temperature and low densities, however, the poor fracture toughness limits their practical application in aerospace field. In this work, a stable Nbss/γNb₅Si₃ bi-phases structure has been designed with TaC doping. Moreover, there are also some nano-γNb₅Si₃ precipitates in the matrix, which show the coherent interface with Nbss phases. In addition, the composite structure greatly enhances the combination properties of Nb-Si superalloys. The optimal values of room temperature fracture toughness are 14.79 MPa·m^1/2, which increase by 26.29% than based alloys. And the room temperature compressive and nanoindentation properties also improve due to the solid solution strengthening. Moreover, the nanoindentation experiment exhibits the plastic work of Nbss and γ(Nb, X)₅Si₃ maintains an upward trend. And the optimal values of elastic modulus are 152.77 GPa and 236.53 GPa for Nbss and γ(Nb, X)₅Si₃ phases, respectively. Furthermore, the nanohardness displays the similar results with the maximum of 5.40 GPa and 12.11 GPa, respectively. At thermal deformation condition, the nano-precipitates can signally affect dislocations movement to increase the strength, and the dislocation slip is the main deformation mechanism in our alloys. Meanwhile, the dislocation walls are also found in brittle γ(Nb, X)₅Si₃ phases, resulting from the dislocations pile-up in the interface.