Effect of Cr Addition on the Microstructure and Roomtemperature Fracture Toughness of Nb-Si Based Ultra-high Temperature Alloys

Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》

张松 郭喜平

Abstract： Four Nb-Si based ultra-high temperature alloys with compositions of Nb-22Ti-16Si-4Hf-3AlxCr (x = 0, 3%, 5% and 10%, atomic fraction) were prepared by vacuum non-consumable arc melting and then heat-treated at 1450℃ for 50 h. The effects of Cr content on the microstructure and room-temperature fracture toughness of the alloys were investigated. The results showed that the Cr addition did not change the crystal structure of the silicide γ(Nb, X)5Si3. The amount of γ(Nb, X)5Si3 rose while that of the eutectic Nbss/γ(Nb, X)5Si decreased with the increasing Cr content. Furthermore, a low melting point of three-phase eutectic composed of Nbss, (Nb, X)5Si3 and Cr2(Nb, X) was observed in Cr-containing alloys and its amount gradually increased with the increasing Cr addition. After 1450℃/50 h heat- treatment, the original Nbss dendrites as well as eutectic colonies disappeared, and the microstructural uniformity was significantly ameliorated. The alloys with 0, 3% and 5% Cr were all composed of phases Nbss and γ(Nb, X)5Si3, while three-phase equilibrium of Nbss, γ(Nb, X)5Si3 and Cr2(Nb, X) was observed in the alloy with 10% Cr. However, the room-temperature fracture toughness of the as-cast alloys exhibited a decreasing trend with Cr addition.

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