Abstract
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)3Si phase → Nbss/(Nb, X)5Si3 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)5Si3 eutectic has the maximum fracture toughness of 13.4 MPa m1/2. The 6 at.% Mo or 2 at.% W addition has little influence on the room-temperature fracture toughness KQ value, but the common addition of 8 at.% Cr, 6 at.% Mo and 2 at.% W can improve room-temperature fracture toughness KQ 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)5Si3 eutectic can prevent the crack propagation and improve the fracture toughness.
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