Tie lines in a two-phase region in the Cu–Ni–Zn system

Abstract

The positions of the f.c.c. + b.c.c. two‐phase region and the f.c.c. + b.c.c. + tetragonal three‐phase region of the Cu–Ni–Zn system have been determined. The position of the latter differs significantly from that determined by Schramm & Vaupel [Metallwirtsch. (1936), 15, 723–726]. Unit‐cell parameters measured by X‐ray powder photography enabled tie lines in the two‐phase region to be drawn. Hence information about the free‐energy surfaces has been derived.

Thermodynamic calculation of phase equilibria in the Cu–Ni–Zn system

“…Fig. 2 is the calculated isothermal section at 600 8C compared with various experimental determinations [4,9,10]. Overall, agreement between the calculation and the experiments is fairly good except for a difference as to the location of the phase boundary a/aCb 1 .…”

“…2. Comparison of the calculated isotherm at 600 8C with various experimental investigations [4,9,10].…”

“…Haworth and HumeRothery [7] determined the a/b equilibrium at 672 8C by microscopic examination combined with chemical analysis. Mayall and co-workers [9,10] did systematic research at 600 8C by using X-ray technique for structural analysis and atomic absorption spectrometer for composition determination, and as a result, the phase relationships in this isotherm covering the phase regions of a, b and b 1 have been well constructed. Besides these, a series of investigations on multiphase diffusion at 775 8C have been performed in the Cu-Ni-Zn system [8,13,14].…”

“…Also in the Ni-Zn system, the L1 0 type of b 1 , originally described by (Ni,Zn) (Zn,VA), was remodeled by a two-sublattice model (Ni,Zn)(Ni,Zn) in the binary system. For the ternary b 1 phase, Cu was permitted to enter the Ni sublattice, leading to (Cu,Ni,Zn)(Ni,Zn), according to its homogeneity range as determined by Mayall and co-workers [9,10]. No phase diagram data are available for the Zn corner, thus the 3 phase in the Cu-Zn and the NiZn 8 in the Ni-Zn system were treated as binary phases.…”

“…However, for the calculation of ternary solid solutions, some binary phases in both Cu-Zn and Ni-Zn systems have to be remodeled. The ternary phase relationships, except for those in the very Zn-rich region, have been well experimentally studied by numerous investigations [4][5][6][7][8][9][10], and will be critically described in this work. On the other hand, the ordering phenomenon within the a-CuNiZn is rather complicated due to the strongly attractive interaction of the nearest Ni-Zn and Cu-Zn pairs and the weakly repulsive one of the Cu-Ni.…”