Refinement of the eutectic composition in the LaB6–VB2 system

Abstract

The LaB6–VB2 alloy with the eutectic structure was obtained by cold crucible induction melting followed by crystallization. The mole ratio of components in the initial powder mixture was 35 : 65. The structure and composition of the LaB6–VB2 material were studied by X-ray diffraction, scanning electron microscopy, and X-ray microanalysis. The composition of the alloy is represented by two boride phases — cubic LaB6 and hexagonal VB2. Two-phase eutectic regions up to 500 μm in size represent a LaB6 matrix filled with 0.8–2.0 μm thick VB2 fibers (filamentary, rod crystals). VB2 fibers are predominantly oriented along the direction of the temperature gradient that appeared when cooling the melt, i.e. from the outer surface of the sample to its center. The integrated phase area analysis was used to determine the eutectic composition: 42 Ѓ} 1 mol% LaB6 and 58 Ѓ} 1 mol% VB2.