Abstract: Nb-10Si and Nb-10Si-xMo(x=5,15) composites at hypoeutectic compositions are prepared by arc-melting, followed by heat treatment at 1200℃ for 100 hours. The microstructures, compositions and the fracture surface of annealed sample are investigated using scanning electron microscopy (SEM) and X-ray energy disperse spectrum (EDS), as well as X-ray diffraction (XRD). The microhardness of Nb-10Si-Mo is determined. Single edge notched bending (SENB) test is used to measure the fracture toughness of Nb-10Si-xMo(x=0,5,15). The effect of Mo addition on the deformability of ductile phase in Nb/Nb₅Si₃ and the fracture toughness of Nb/Nb₅Si₃ in situ composites is further studied.

Key words: Nb/Nb₅Si₃ composites, fracture toughness, single edge notched bending (SENB), Vickers hardness, metastable phase