Variation in morphology and crystallographic orientation of directionally solidified Nb–Si based alloys at high withdrawal rates

Nb–Si based alloys are directionally solidified at the withdrawal rates of 100, 500 and 1000 μm/s respectively. At the withdrawal rate of 100 μm/s, the eutectic presents well-coupled lamellar structure. Besides, Nb_SS and γ-(Nb, X)₅Si₃ phases are well oriented along [111]_Nb and [0001]_γ crystallographic orientations respectively and the crystallographic orientation relationship of <111>_Nb//<0001>_γ, {110}_Nb//{101‾0}_γ is obeyed. When the withdrawal rate reaches to 500 μm/s, the eutectic begins to transform into irregular fibrous structure and no crystallographic orientation relationship can be detected, and it is caused by the variation in growth direction of Nb_SS phases from [111]_Nb to [100]_Nb.