Nb-Ti-Si-Cr-Hf-Al-B-Y superalloy was prepared by vacuum consumable arc melting

and its ambient fracture toughness and mechanical properties were measured. The constituent phases

microstructure

composition distribution and fracture morphology at different positions in the alloy ingot were observed by XRD （X-ray diffraction）

SEM （scanning electron microscope） and EDS （energy dispersive spectrum）. The results reveal that microstructure of the alloy is mainly composed of primary （Nb

X）5Si3 （where X represents Ti

Hf and Cr） and Nbss/（Nb

X）5Si3 eutectic colonies （Nbss denotes Nb solid solution）

in which primary silicide is distributed discontinuously in the shape of regular blocks or plates and Nbss/（Nb

X）5Si3 eutectic colonies exhibit typically lamellar or petal-like morphologies. Si content is increased from the edge to the center while the Nb and Ti contents are higher in the edge than in the center of the ingot. Solubility of Cr and Al in Nbss is higher than in （Nb

X）5Si3 while Hf mainly is segregated in （Nb

X）5Si3. Ambient fracture toughness and tensile strength of the arc-melted alloy reach 10.72MPa.m1/2 and 297.12 MPa

respectively. In addition

ambient fracture mechanism is characterized by brittle quasi-cleavage mode in both fracture and tensile morphology.