Microstructures and room temperature fracture toughness of Nb/Nb5Si3 composites alloyed with W, Mo and W–Mo fabricated by spark plasma sintering

•Microstructure of Nb/Nb5Si3 composite alloyed with W and Mo is change obviously.•W and Mo elements can solid solution in Nb and Nb5Si3 phase respectively.•Alloyed with W and Mo together, the solid solubility of Nb5Si3 phases is undetected.•The Nb/Nb5Si3 composite alloyed with W and Mo together has high fracture toughness.

Microstructures and room temperature fracture toughness of Nb/Nb5Si3 composites alloyed with W, Mo and W–Mo fabricated by spark plasma sintering were investigated. The microstructures were examined using scanning electron microscope (SEM). X-ray diffraction (XRD) was performed on the bulk specimens for identification of phases. The chemical species were analyzed using electron-probe micro-analysis (EPMA). Results indicated that the microstructures of Nb/Nb5Si3 composites alloyed with W or Mo is unaltered, including primary Nb and eutectic mixtures of Nb and Nb5Si3, and the coarse and fine eutectic mixtures. The W and Mo elements solid solution in Nb and Nb5Si3 phase are detected. But that alloyed with W and Mo together, The microstructures are change obviously, including Nb phase, the solid solubility phases of W and Mo atoms in Nb, and the solid solubility phases of Nb atoms in W are also found, but the solid solubility phenomenon of Nb5Si3 phases is not detected. The microhardness of Nb and Nb5Si3 phases increases obviously because of solid solution strengthening. The Nb/Nb5Si3 composite alloyed with W and Mo together hashing high fracture toughness is attributable to the big eutectic Nb and interface of eutectic phases, which can bear large deformation to absorb the crack energy and form the decohesion between eutectic phases.