Microstructure evolution and fracture toughness of Nb-Si-Ti based alloy with Cr, Mo and W elements addition

This paper deals with microstructural evolutions, phase constitutions and fracture toughness of Nb-16Si-22Ti-(6Mo/8Cr/2W) alloys using the vacuum non-consumable arc-melting. The results show that the addition of 6 at. % Mo or 8 at.% Cr promotes the eutectic reaction of (Nb, X)(3)Si phase -> Nbss/(Nb, X)(5)Si-3 eutectic. The common addition of 8 at.% Cr and 6 at.% Mo leads to the microstructure transform from hypoeutectic microstructure to near-eutectic microstructure. The Nb-16Si-22Ti-8Cr alloy with coupled structure of Nbss/(Nb, X)(5)Si-3 eutectic has the maximum fracture toughness of 13.4 MPa m(1/2). The 6 at.% Mo or 2 at.% W addition has little influence on the room-temperature fracture toughness K-Q value, but the common addition of 8 at.% Cr, 6 at.% Mo and 2 at. % W can improve room-temperature fracture toughness K-Q value. The high content of Nbss phase and Nbss dendritic crystal in the matrix can contribute to fracture toughness of NbSi alloy. The coupled structure of Nbss/ (Nb, X)(5)Si-3 eutectic can prevent the crack propagation and improve the fracture toughness.

Automated summary

The addition of different alloy elements can lead to changes in the microstructure and fracture toughness of Nb-16Si-22Ti alloys. Among them, the Nb-16Si-22Ti-8Cr alloy has the maximum fracture toughness of 13.4 MPa m(1/2).