LAUSR

Abstract Multi-element Nb–Si based alloys with nominal compositions of Nb-xTi-15Si–5Cr-1.5Hf-1.5Zr (x = 0, 10, 20 and 25 at. %) were simultaneously directionally solidified at 2050 °C. When the Ti addition contents are 0 10 at. %, the microstructure is composed of primary α-(Nb, X)5Si3 and NbSS/α-(Nb, X)5Si3 eutectic. When the Ti addition content reaches to 20 at. %, primary γ-(Nb, X)5Si3 appears and NbSS/γ-(Nb, X)5Si3 eutectic is formed at NbSS/α-(Nb, X)5Si3 eutectic cellular boundary or around primary γ-(Nb, X)5Si3. When the Ti addition increases to 25 at. %, α-(Nb, X)5Si3 is completely substituted by γ-(Nb, X)5Si3. Besides, the increasing Ti addition content increases the area fraction of primary (Nb, X)5Si3 and promotes the refinement of NbSS/(Nb, X)5Si3 eutectics. The crystalline orientation relationship between NbSS and α-(Nb, X)5Si3 is Nb∥[001]α and {110}Nb∥{310}α when the Ti addition contents are ranged from 0 to 20 at. %. When the Ti addition content is 20 at. %, there exists no crystalline orientation relationship between NbSS and γ-(Nb, X)5Si3. When the Ti addition content reaches to 25 at. %, the crystalline orientation relationship between NbSS and γ-(Nb, X)5Si3 is Nb// γ and {110}Nb// { 10 1 ‾ 0 } γ . With increasing Ti addition, the orientation deviation degree between NbSS and (Nb, X)5Si3 decreases, which indicates that the coupling degree of the eutectic increases at higher Ti addition contents.