Thermodynamic modelling of the Co–Y system

Abstract

The Co-Y system was critically assessed by means of the CALPHAD technique. The solution phases (liquid, body-centred cubic, face-centred cubic and hexagonal close-packed) were modelled with the Redlich-Kister equation. The intermetallic compounds Co 17 Y 2 and Co 5 Y, which have a homogeneity range, were treated as one phase with the formula (Co 2 ,Y)(Co 2 ,Y) 2 Co 15 , based on their crystal structures, by a three-sublattice model with Co 2 and Y on the first and second sublattices and Co on the third one, respectively. The others Co were treated as stoichiometric compounds. A set of self-consistent thermodynamic parameters of the Co-Y system was obtained.

Thermodynamic modeling of the Co–Ni–Y system

“…Each of the binary systems involved, Co-Ni [7], Co-Y [8], and Ni-Y [9] has been assessed, and self-consistent thermodynamic descriptions were obtained while the Ni-Y system [9] is re-assessed by some minor adjustments.…”

“…1 shows a calculated phase diagram using the thermodynamic description of Fernandez Guillermet [7], in which the liquidCfcc two-phase field is extremely narrow. The thermodynamic modeling of the Co-Y system has been recently carried out by Du and Lü [8]. As shown in Fig.…”

“…The homogeneity regions of Co 17 Y 2 and Co 5 Y could be characterized by a CaCu 5 -type of lattice in which part of the Ca sites are occupied by pairs of Co atoms. Du and Lü [8] described both the compounds Co 17 Y 2 and Co 5 Y as one phase with the formula (Co 2 ,Y)(Co 2 ,Y) 2-Co 15 by a three-sublattice model [10][11][12] with Co 2 and Y on the first and second sublattices and Co on the third one, respectively. The compounds Ni 17 Y 2 and Ni 5 Y in the Ni-Y system are treated as the stoichiometric compounds, which have the Ni 17 Th 2 -type and CaCu 5 -type structures, respectively, by Du and Zhang [9].…”

“…T Co m Y n c and b Co m Y n and T Ni m Y n c and b Ni m Y n , respectively, which are taken from the measured critical temperature and the mean Bohr magnetic moment per mole of formula units [1,8]; i T M m Y n cCo;Ni:Y and i b M m Y n Co;Ni:Y are the ith magnetic interaction parameters between elements Co and Ni on the M sublattice, here set to be zero as a result of a lack of experimental data.…”

“…A careful examination of existing thermodynamic descriptions of the binary Co-Ni [7], Co-Y [8], and Ni-Y [9] systems were made. The modification of the Ni-Y system resulted in somewhat different values of the thermodynamic parameters of the terminal solution phases bcc, fcc, hcp, and compounds NiY, Ni 2 Y 3 , and NiY 3 , but not in any changes in calculated phase diagram or thermodynamic properties.…”