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

 

Chem. Met. Alloys 3 (2010) 208-219

 

Taras MIKA, Bogdan KOTUR

 

The phase equilibria in the Al-rich region of the {Y, Gd}NiAl 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}NiAl 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 YNiAl 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