On the stability of the V5B6-phase

• Published in: Journal of alloys and compounds Vol. 370; no. 1-2; pp. 164 - 168
• Main Authors: NUNES, Carlos Angelo, DE LIMA, Belmira Benedita, CARVALHO COELHO, Gilberto, ROGL, Peter, ATSUSHI SUZUKI, Paulo
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier 12-05-2004
• Subjects: Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Scanning electron microscopy; Phase diagrams; Melting; Intermetallic compounds; Backscattering; Intermetallics; X-ray diffraction; High temperature alloys; XRD; Heat treatments; Cast alloy; Casting; Borides
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2003.09.117

The currently assessed V-B phase diagram indicates a peritectoid formation at 1727DGC (V3B4 + VB DB V5B6) for the V5B6 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 2000DGC 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 + V5B6 DB V5B(, 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 V5B6-phase at 2000DGC, in disagreement with the currently accepted V-B phase diagram.