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

Under directional growth, the eutectic transformation L reversible arrow Al3Nb + Nb2Al + Nb(Ni(1-x)Alx)(2) resulted in a very organized three phase microstructure. While many features of this eutectic have already been explored, crystal-lographic 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(Ni1-xAlx)(2) phases. It was observed that the Nb(Ni1-xAlx)(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(Ni1-xAlx)(2) (x = 0.85) phase are a = 5.031 angstrom and c = 8.298 angstrom and these lattice parameters depend on Al content.