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Nb-Si system in-situ composites with nominal composition of Nb-21Ti-16Si-7Cr-3Al-2Hf(mole fraction,%) were prepared by directional solidification technology in an optical floating zone furnace at the growth rates of 3,5,8 and 12 mm/h.The microstructures and mechanical properties were investigated as a function of the growth rate.The results show that the solidification microstructures consist of Nb solid solution(Nbss),α-Nb_5Si_3 andβ-Nb_5Si_3.Silicides with high aspect ratio grow continuously and straightly when the growth rate is 5mm/h;lower or higher growth rates are disadvantageous for the formation of favorable directional microstructures.The compressive strength at 1 250℃and room-temperature fracture toughness of the specimen with the growth rate of 5 mm/h that exhibits excellent mechanical properties are 415 MPa and 22.4 MPa·m~(1/2),respectively.
Nb-Si system in-situ composites with nominal composition of Nb-21Ti-16Si-7Cr-3Al-2Hf (mole fraction,%) were prepared by directional solidification technology in an optical floating zone furnace at the growth rates of 3,5, 8 and 12 mm / h. The microstructures and mechanical properties were investigated as a function of the growth rate. The results show that the solidification microstructures consist of Nb solid solution (Nbss), α-Nb_5Si_3 and β-Nb_5Si_3.ilicilic with high aspect ratio grow continuously and straightly when the growth rate is 5 mm / h; lower or higher growth rates are disadvantageous for the formation of favorable directional microstructures. compressive strength at 1 250 ° C and room-temperature fracture toughness of the specimen with the growth rate of 5 mm / h that exhibits excellent mechanical properties are 415 MPa and 22.4 MPa · m ~ (1/2), respectively.