Microstructural Evolution and Room Temperature Fracture Toughness of a Nb-Ti-Si-Cr-AI-Hf-Y Alloy Prepared by Directional Solidification

摘要

The Nb-24Ti-12Si-14Cr-2Al-2Hf-0.1 Y (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 ofNbss, Cr_2Nb and eutectics (Nb_(ss)+Nb_5Si_3), 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 Cr_2Nb tended to spheroidize. The sample prepared by higher withdrawal rate plus heat treament shows higher average K_Q 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 Nb_5Si_3 and Cr_2Nb.