Isothermal Section of the V-Si-B System at 1600 A°C in the V-VSi2-VB Region

In recent years, the Me-Si-B (Me-metal) ternary systems have received considerable attention aiming at the development of high-temperature structural materials. Assuming that any real application of these materials will rely on multicomponent alloys, as is the case of Ni-base superalloys, phase equilibria data of these systems become very important. In this work, results are reported on phase equilibria in the V-Si-B system, and are summarized in the form of an isothermal section at 1600 A degrees C for the V-VSi2-VB region. Several alloys of different compositions were prepared via arc melting and then heat-treated at 1600 A degrees C under high vacuum. All the materials in both as-cast and heat-treated conditions were characterized through x-ray diffraction, scanning electron microscopy, and selected alloys via wavelength dispersive spectroscopy. A negligible solubility of B in the V3Si, V5Si3 (T-1), and V6Si5 phases as well as of Si in V3B2 and VB phases was noted. Two ternary phases presenting the structures known as T-2 (Cr5B3-prototype) and D8(8) (Mn5Si3-prototype) were observed in both as-cast and heat-treated samples. It is proposed that at 1600 A degrees C the homogeneity range of T-2 extends approximately from 5 at.% to 12 at.% Si at constant vanadium content and the composition of D8(8) phase is close to V59.5Si33B7.5 (at.%).