COST 507 - Repositório Aberto da Universidade do Porto

eviews by Rivlin and Raynor [81 Riv] and by Ghosh [92Gho] are based on these
experiments. Takeda and Mutuzaki state that the evidence for some of the reactions is
circumstantial, and they also found it difficult to distinguish some of the phases by
etching. Their phase analysis are also inaccurate and do not agree with later work for
the more known phases. In this assessment emphasis has thus been placed on the
temperatures measured by Takeda and Mutuzaki as opposed to their reported
compositions. More data exists in the aluminium rich part of the diagram, and
experiments by Phillips [59Phi], Phragmen [50Phr], Munson [67Mun], Dons [84Don],
Gringer [87Gri], Stefaniay [87Ste], Oscarsson [880sc] and others have been used for
this part of the diagram.
The calculated liquidus diagram is shown in Fig 1.. Takeda and Mutuzaki's diagram is
generally reproduced, but there are differences. The primary precipitation field for
Fe 2 Si is more narrow and the Fe 2 Si phase is also found to precipitate from the ternary
liquid. This is mainly caused by differences in the binary Fe-Si diagrams. Moving into
the central part of the diagram, the main differences are caused by the phases
denominated τ_1 and τ_3. The primary field of the τ_1 phase is smaller compared to
the experimental diagram, but it is peritectic and the reactions around it are in
agreement with the determinations of Takeda and Mutuzaki. Since this part of the
diagram is rather inaccurate, the fit is regarded as satisfactory.
In the calculated diagram t_3 melts congruently, while Takeda and Mutuzaki have
determined the phase to be peritectic. Their results in one of the invariant points
surrounding its primary field is a eutectic as opposed to a peritectic. The calculations
are probably wrong on this point since the reaction involves the FeSi phase and the Fe-
Si system is due to be revised. Therefore little effort was put into forcing the phase to
become peritectic in the calculations at this stage. In any case further experimental
studies are necessary to establish the composition and types of reactions involved in
the invariant points in this region. The ordered bcc_.b2 phase has been used in the
assessment.
The aluminium rich region of the diagram agrees well with the present knowledge of
the phase diagram. The liquidus surface does not reproduce Takeda and Mutuzaki, but
agree with later results, especially Munson [67Mun] and Stefaniay [87Ste]. Several
earlier sources have not distinguished between the hexagonal alpha-AlFeSi and the
cubic alpha-AlMnFeSi phases. For this reason only results that clearly state the
presence of the hexagonal phase have been used in this assessment. The primary field
for alpha-AlFeSi precipitation has therefore been greatly reduced as compared to
earlier diagrams of Phillips [59Phi] and Takeda and Mutuzaki [40Tak].
For the hexagonal alpha phase, data given by Mondolfo [76Mon] has been used in the
assessment combined with isothermal data at 600°C [87Ste]. Mondolfo states that the
alpha phase contains 7.0wt% Si regardless of which equilibrium it is involved in. This
cannot be correct if the phase has a homogeneity range with respect to Si. The
calculated values range form 6.2 to 7.2 wt% Si are thus well within the experimental
error. In a later study it was found that the Si content in the alpha phase after rapid
cooling is 6-11 wt% while it lays in the range 6-9.5 wt% at 600°C [87Ste]. Armand
[54Arm] and Black [55Bla] have determined the Si content in the hexagonal alpha
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