Refining and toughening mechanism of Nb-16Si-20Ti-2ZrC-xY composite materials by constitutional supercooling and edge-to-edge model

To explore the mechanism of the refinement and toughening of Nb-Si-based composites with different Y contents, Nb-16Si-20Ti-2ZrC-(0, 0.05, 0.1, 0.5) Y composites were prepared by arc melting. The results show that Y has a positive effect on the shift of the eutectic point and promotes it moving to the low Si side. Adding 0.1 at.% Y refines the Nbss phase from 38.7 to 11.2 μm. Y₂O₃ forms due to the strong affinity of Y to O. The edge-to-edge model predicted that there was no phase relationship between Y₂O₃ and Nbss and primary γ-(Nb,X)₅Si₃, which was verified by TEM. Y refines the Nbss and the Nbss/γ-(Nb,X)₅Si₃ cluster with compositional supercooling. As Y content increased, the fracture toughness at room temperature increased and decreased. When the Y content was 0.1 %, the K_Q value reached 17.2 MPa·m^1/2. The internal oxygen consumption of Y and the refinement of Nbss lead to the toughness improvement of the Nbss phase, promoting the formation of a large number of dimples. Microcracks form in the fine γ-(Nb,X)₅Si₃ of eutectoid cluster, which hinder the primary crack growth and enhance the ambient fracture toughness. These findings are of great significance for the further development of high-performance Nb-Si-based matrix composites.