Competitive growth of nano-lamellae Nb/Nb₃Si eutectics with enhanced hardness and toughness

Here we propose to employ electron beam surface melting (EBSM)to refine microstructural length scale and obtain suited microstructure morphology of Nb-Si based alloys. As characterized by scanning transmission electron microscopy (STEM)and atom probe tomography (APT), nano-lamellar eutectics are created in Nb-20Si (at.%)alloys upon EBSM. Theoretical analysis based on the competitive growth models demonstrates the preferred formation of Nb solid solution (Nbss)/Nb₃Si eutectics under selected processing parameters. The large cooling rate during EBSM, higher than 8 × 10⁴ K/s, promotes the formation of the nano-scale eutectics. Compared to the initial coarse eutectics by arc melting, simultaneous enhancement of hardness and fracture toughness is enabled owing to the controlled microstructural length scale and morphology.