Effect of V addition on microstructure and mechanical property in the Nb-Si alloy system

Microstructure and mechanical property of vanadium-added two-phase alloys consisting of α-Nb5Si3 phase and Nb solid solution (Nbss) were investigated in terms of a variation of chemical composition and compression test at room temperature and at 1773 K. The equilibrium phase field of α-Nb5Si3 and Nbss in the Nb-Si-V ternary alloy system was examined at 1773 K using scanning electron microscopy equipped with wavelength dispersive X-ray spectroscopy and X-ray diffraction. The α-Nb5Si3 phase formed in the Nb-Si-V system was extended along the Nb5Si3-V5Si3 pseudo-binary line without a solubility range of Si at 1773 K, while vanadium is soluble continuously along the Nb-V phase boundary with Si solubility of about 0.7 at%. It is observed that volume fraction ratio of the present alloy is predominantly dependent on Si content but exhibited no dependence on vanadium content. With increasing vanadium content, primary α-Nb5Si3 and Nbss phases became finer through the whole composition studied. The 0.2% offset yield strength at room temperature increased with increasing volume fraction of α-Nb5Si3 phase and with increasing vanadium content in Nbss. In contrast, the 0.2% offset yield strength at 1773 K decreased with increasing vanadium content in Nbss. Details will be discussed in correlation with microstructure, phase relation and mechanical property