On the stability of the V5B6-phase (original) (raw)

The currently assessed V-B phase diagram indicates a peritectoid formation at 1727 • C (V 3 B 4 + VB ⇔ V 5 B 6) for the V 5 B 6 boride. The observation of this phase in several as-cast V-B alloys has lead us to a systematic evaluation of its stability, specially its possible formation from the liquid. In this work, V-B alloys (52-56 at.% B range) were produced through arc melting and heat-treated under high vacuum at 2000 • C for 2 h. The materials in both as-cast and heat-treated conditions were characterized through scanning electron microscopy (SEM) (backscattered electron (BSE) images) and X-ray diffraction (XRD). The features observed in the as-cast samples allowed us to conclude that this phase should be formed from the liquid through the L + V 3 B 4 ⇔ V 5 B 6 peritectic reaction. In spite of not reaching equilibrium condition during heat-treating, the results from the characterization of heat-treated samples have indicated the stability of the V 5 B 6-phase at 2000 • C, in disagreement with the currently accepted V-B phase diagram.