Phase Equilibria of the Al–V–RE (RE = Gd, Ho) Systems at 773 K (500 °C)

Abstract

Isothermal section of the Al–V–RE (RE = Gd, Ho) ternary systems at 773 K (500 °C) was investigated over the whole concentration range by means of X-ray diffraction and scanning electron microscopy equipped with energy dispersive X-ray analysis. The crystal structures of the Al₄₃Mo₄Ho₆-type ternary compounds Al₄₃V₄RE₆ were determined with Rietveld refinement method. The intermetallic compound Al₄₃V₄Gd₆ belongs to the Space group P6₃/mcm, with cell parameters of a = b = 1.0996(6) nm, c = 1.7813(9) nm, α = β = 90 deg, γ = 120 deg, and volume of unit cell of 1.8658(9) nm³. At 773 K (500 °C), all the Al-rich ternary alumides, i.e., Al₄₃V₄Gd₆, Al₂₀V₂Gd, Al₄₃V₄Ho₆, and Al₂₀V₂Ho appear without any significant homogeneity region. Five binary compounds, i.e., AlV₃, Al₄Gd, Al₁₇Gd₂, Al₁₇Ho₂, and AlHo₂ reported in the literature were not found. Fifteen and 14 ternary phase fields have been identified in the isothermal section of the Al–V–Gd and Al–V–Ho ternary systems, respectively. The solid solubility of V in Al₂RE₃, AlRE, and Al₂RE amounts to approximately 1.0 at. pct to 2.0 at. pct, whereas the solid solubility of Al in V is approximately 39 at. pct.