COST 507 - Repositório Aberto da Universidade do Porto

[96Sei] Excess Gibbs energy coefficients for the binary systems, Mn-Y, Mn-Zr and Y-Zr
have been optimised using a least squares method applied to all of the experimental data
in the literature plus additional data from new experiments. Combining these with the
COST 507 data-sets for Mg-Mn and Mg-Zr plus the Mg-Y data-set from Kuang has
enabled extrapolated phases diagrams to be computed for the ternary systems Mg-Mn-Y,
Mg-Mn-Zr, Mg-Y-Zr and Mn-Y-Zr. Selected experiments carried out on three of these
ternaries show good agreement with the calculated boundaries. On this basis a
thermodynamic data-se for the Mg-Mn-Y-Zr system has been assembled which enables
several different types of phase diagrams and sections to be computed for the quaternary
system. As examples of the kind of diagrams of practical importance that can currently
be obtained with modern thermodynamic software for multicomponent alloy systems,
calculated phase fraction versus temperature diagrams have been presented for two
quaternary alloy compositions, Mg-lwt% Mn-lwt% Zr with 5 and 10 wt% Y
respectively. The data presented result from the cooperative network "MSIT Trainer
Network on the Constitution of Engineering Materials", operating under EU Human
capital and Mobility Programme, TMR.
Aluminum Alloys
[96Bor] To complete the investigation and the thermodynamic optimization of the Al
alloys with trivalent R, the study of La-Al system is now in progress. The examination of
the Yb-Al alloys has also been started. This system is different from those given by the
trivalent Rs: only two compounds are formed. Even if in both cases the minimum in the
trends of Af orm H° versus composition corresponds to the RAJ2 stoichiometry, the
different reactivity of Al with La and Yb is also reflected by the disparity between the
values of the Af orm H°: -50.512 kJ/mol at. for LaAl 2 and -39.512 kJ/mol at. for YbAl 2 .
These results are discussed and compared with those of other similar R-Al compounds.
An assessed version of different R-Al systems has been presented.
[96Sac2] As a contribution to the understanding of the R-Al diagrams, an assessed
version of the Gd-Al system has been prepared and discussed. As a consequence the
experimental investigation of the Gd-rich part of the Gd-Al diagram has been carried out.
The coordinates of the Gd-rich eutectic, the lowering of the allotropie transformation
temperature of the gadolinium by additions of Al and the melting behaviours of the Gdrich
compounds have been particularly discussed.
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