Crystallographic features of the Al3Nb, Nb2Al and Nb(Ni1−XAlX)2 phases in a directionally solidified ternary eutectic microstructure

Highlights: • The eutectic growth resulted in a well-organized rod-like three-phase arrangement. • XRD and Rietveld refinement allowed precise calculations of lattice parameters. • Laves phase lattice parameters depend on Al content. -- Abstract: Under directional growth, the eutectic transformation L ⇄ Al₃Nb + Nb₂Al + Nb(Ni_1−xAl_x)₂ resulted in a very organized three phase microstructure. While many features of this eutectic have already been explored, crystallographic details of its phases are still missing. This paper aims to investigate composition and crystallographic features of a directionally solidified eutectic made up of the Al₃Nb, Nb₂Al and Nb(Ni_1−xAl_x)₂ phases. It was observed that the Nb(Ni_1−xAl_x)₂ intermetallic phase has the C14 structure, with composition 56.91 ± 0.43 at.% Al, 10.11 ± 0.12 at.% Ni and 32.98 ± 0.53 at.% Nb. Selected area diffraction in a transmission electron microscope permitted interplanar spacings to be determined and values obtained are consistent with those in the literature. Accurate lattice parameters were determined using powder X-ray diffraction combined with Rietveld refinement. It was found that the lattice parameters of the Nb(Ni_1−xAl_x)₂ (x = 0.85) phase are a = 5.031 Å and c = 8.298 Å and these lattice parameters depend on Al content.