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

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.