Phase equlibria in the {Y, Gd}–Ni–Al ternary systems in the 65-100 at.% Al range at 773 K: a reinvestigation

Chem. Met. Alloys 3 (2010) 208-219

https://doi.org/10.30970/cma3.0171

Taras MIKA, Bogdan KOTUR

The phase equilibria in the Al-rich region of the {Y, Gd}–Ni–Al ternary systems at 773 K have been reinvestigated using XRD, microstructure and X-ray microprobe analysis. Four intermetallic compounds: 1 - R₃Ni₅Al₁₉ (structure type Gd₃Ni₅Al₁₉), 2 - R₄Ni₆Al₂₃ (Y₄Ni₆Al₂₃), 3 - RNi₃Al₉ (YNi₃Al₉) and 4 - RNiAl₄ (YNiAl₄), exist in both systems. It was shown that the thermodynamic equilibrium state of the samples could be reached after a relatively long heat treatment (up to four months). This is probably the main reason for some contradictions in the literature on the {Y, Gd}–Ni–Al phase diagrams. The crystal structure of the Y₃Ni₅Al₁₉ ternary compound (Gd₃Ni₅Al₁₉ type, space group Cmcm) was refined by the Rietveld method from powder X‑ray diffraction data. The refined cell parameters are a = 0.40713(1) nm, b = 1.5957(3) nm, c = 2.7052(6) nm.

Isothermal cross-section of the Y–Ni–Al ternary system at 773 K, nominal composition of some alloys and their numbers are according to [10]. Ternary compounds: 1 – Y₄Ni₆Al₂₃, 2 – YNiAl₄, 3 – YNi₃Al₉.

Keywords

Rare-earth ternary systems / Phase equilibria / Intermetallic compounds