Microstructure evolution and mechanical properties of Nb–Si based alloy processed by electromagnetic cold crucible directional solidification

• The DS samples were fabricated by ECCDS.
• With increasing withdrawal rate, the microstructure became finer.
• With increasing withdrawal rate, KQ first decreased and then increased.
• With increasing withdrawal rate, the tensile strength (1250 °C) increased.

In this paper, the samples with the composition of Nb–22Ti–16Si–3Cr–3Al–2Hf (at.%) have been successfully processed by electromagnetic cold crucible directional solidification, and the microstructure evolution and mechanical properties of the samples were investigated as a function of withdrawal rate. The microstructures of all the samples were composed of primary Nbss, Nbss + α-(Nb, Ti)5Si3 eutectic and Nbss + Ti-rich (Nb, Ti)5Si3 eutectic. With the increase of withdrawal rate, the microstructure became finer, which could be characterized by the decreased mean diameter of cellular eutectic, mean diameter of eutectic Nbss particles and mean interphase spacing. Meanwhile, the room temperature fracture toughness decreased first, and then increased; the high temperature tensile strength increased gradually. The volume fraction, size and aspect ratio of Nbss and the number of Nbss/(Nb, Ti)5Si3 interfaces codetermined the fracture toughness. The more number of Nbss/(Nb, Ti)5Si3 interfaces was conducive to impeding the movement of dislocation, which caused the improvement of tensile strength.