Synergistic effect of (Sm + Tb) microalloying on microstructure evolution and mechanical properties of Nb-Si-based alloys

The synergistic effect of Sm and Tb dual rare-earth microalloying on the microstructure and room-temperature mechanical properties of Nb-Si-based alloys was investigated. Results indicate that Sm addition promotes microstructural transition from an irregular coarse eutectic to a broken eutectic, eventually into a fine eutectic. In contrast, Tb addition facilitates the formation of Tb₂O₃, which not only purify the matrix but also act as a heterogeneous nucleation site to promote the precipitation of Nb₅Si₃. This results in Tb₂O₃ particles being distributed around the silicides. The refined eutectics consume energy of crack propagation utilizing frequent bridging and deflection behaviors. Combining altering eutectic morphology to enhance crack propagation resistance and purifying the matrix, the alloy exhibits a simultaneous enhancement in both strength and toughness. The 0.8Sm-0.2 Tb alloy achieves a synergistic improvement in both compressive strength and fracture toughness, with the compressive strength reaching 1769 MPa, representing a 25.4% increase, and the fracture toughness reaching 13.13 MPa·m^1/2, marking a 61% enhancement. This study provides a reliable theoretical and experimental foundation for the development of high-performance Nb-Si-based alloys.