Microstructure and mechanical properties of Nb[sbnd]16Si alloys with Zr additions

Abstract

To optimize the microstructure and fracture toughness of NbSi based alloys, the effect of Zr addition on the microstructure and mechanical properties was investigated in Nb16Si alloy. The results show that Zr element promotes the sluggish eutectoid reaction of (Nb, Zr)3Si → Nbss + α-(Nb, Zr)5Si3, and Nb-16Si-8Zr alloy only contains Nbss and α-(Nb, Zr)5Si3 phases. From the energy point of view, as the Zr content reaches 4 at.%, (Nb,X)5Si3 phase is more stable than (Nb, X)3Si phase. With the increase of Zr content, the fracture toughness increases since high Zr content refines eutectic structure and increases the content of primary Nbss. The thickness of primary Nbss has a strong influence on crack propagation. Most of the cracks can destroy primary Nbss phase with the thickness of (20 ± 2) μm and continue to propagate in the original direction. However, it will deflect when it intersects primary Nbss phase with a thickness of about (30 ± 2) μm. The improvement of compressive properties was caused by solid solution of Zr.