Abstract
To improve microstructure and fracture toughness of MASC alloy, the effects of element substitution of Zr for Hf on the microstructure and room-temperature fracture toughness in Nb-24.7Ti-16Si-xHf-yZr-2.0Cr-1.9Al (x + y = 8.2) alloys have been investigated in this study. The results show that the substitution of Zr for Hf in MASC alloy promotes the eutectic reaction of (Nb, X)3Si phase → Nbss/γ(Nb, X)5Si3 eutectic, and shifts the eutectic point to higher Si content, which leads the microstructure transformation from hypereutectic structure to nearly eutectic structure. The primary γ(Nb, X)5Si3 phase content decreases and Nbss phase content increases with the increase of Zr content. The room-temperature fracture toughness increases with the increase of Zr content, and the room-temperature fracture toughness values of 4Zr-4.2Hf, 6Zr-2.2Hf and 8.2Zr-0Hf alloys are 16.03–16.29 MPa m1/2. The room-temperature fracture toughness value of 16.29 MPa m1/2 is the highest value in the nondirectionally solidified Nb-Si based alloys.
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