Abstract
The Nb-24Ti-12Si-14Cr-2Al-2Hf-0.1Y (at.%) alloys were fabricated by directional solidification with selected withdrawal rate 1.2 and 18 mm/min, followed by a heat treatment at 1375 °C for 10 h. The microstructure of directional solidified samples were composed of NbSS, Cr2Nb and eutectics (NbSS+Nb5Si3), aligning with the growth direction. After heat treatment, the NbSS in the eutectic structures and NbSS dendrites were connected to form the matrix, and the silicide and Cr2Nb tended to spheroidize. The sample prepared by higher withdrawal rate plus heat treament shows higher average KQ values. The results suggested that the Nb-Si based alloy showed higher room-temperature fracture toughness when the microstructure consists of continuous NbSS distributed with finer Nb5Si3 and Cr2Nb.
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