COST 507 - Repositório Aberto da Universidade do Porto

The assessed excess Gibbs energy parameters in the liquid phase showed the existence
of the miscibility gap. The excess Gibbs energy parameters in the Fcc_Al phase were
not optimised. Table 2 shows the assessed parameters in the Cu-Li-Mg system.
Table 2. The assessed excess Gibbs energy parameters in the Cu-Li-Mg system
PHASE
Liquid
Liquid
Liquid
Bcc A2
Cu 32 Li 8 Mg 60 ( τ )
G(Laves_C15,Cu:Li;0)
G(Laves_C15,Mg:Li;0)
L(Laves_C15,Cu:Li,Mg;0)
L
Lo
L,
U
Lo
A,G
G
G
Lo
A
14191.577
14191.577
14191.577
1764.073
-9005.163
25000.000
30000.000
-55000.000
B*T
-
-
-
-
-
-
-
-
The values in Table 2 were assessed using the temperatures of the phase
transformations and verified with the enthalpy values obtained. The assessed
parameter of the Bcc_A2 phase was probably too low because there was no significant
solid solubility of copper both in the copper-lithium and the copper-magnesium
systems. For the same reason the Hcp_A3 phase was considered as a binary phase.
The optimisation of the Laves_C15 phase was carried out manually and yielded one
interaction parameter as L(Laves_C15,Cu:Li,Mg;0) = -55000.
2 The Cu-Mg-Zr system
2.1 Introduction
Baikov Institute of Metallurgy investigated the Cu-Mg-Zr system up to the amount of
50 wt.% Mg and 50 wt.% Zr using methods as light microscopy, X-ray phase analysis,
local X-ray spectral analysis, and differential thermal analysis. One ternary phase was
found in the system. According to local spectral analysis, the composition of the
ternary phase was estimated as 50 at.% Cu, 25 at.% Mg, and 25 at.% Zr. Moreover,
the phases from the binary systems as Cu-Mg and Cu-Zr could be distinguished in the
studied alloys. The substantia] homogeneity ranges of some other phases were also
established. The binary compounds Cu 5 Zr and Cu 5 iZr| 4 exist in the solution up to the
amount of 3 at.% Mg. The phase Cu 2 Mg exists in the solution up to the amount of 2.5
at.% Zr. The phase equilibria in the solid state between ternary phase, binary phases,
and Cu solid solution were determined. Two invariant phase reactions near Cu-rich
corner were discovered, as well. Using the experimental results, the isothermal section
of the phase diagram at 500 °C and the polythermal section in the composition of 90
wt.% Cu were constructed in this study [96Boc].
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