COST 507 - Repositório Aberto da Universidade do Porto

the observed A2-B2 ordering. This paper compares thermodynamically calculated Ti-
Al-V results from the present assessment with the original experimental data points.
2 Data Assessment
2.1 Isothermal Sections
Figures 1 and 2 compare the calculated boundaries at 1573K and 1473K with the data
points given by Kikuchi and co-workers [93Nak]. Figures 3-6 and 8 show the
experimental tie-line and tie-triangle data points reported by Ahmed and Flower
[94Ahml] superimposed on the calculated isothermal sections at 1473K, 1173K,
1073K, 973K and 873K respectively. Figure 7 compares the calculated boundaries
with those from Paruchuri and Massalski for 900K [91 Par]. Figure 9 gives the
calculated Ti-Rich corner at 873K with the experimental data from [88Mae].
2.2 Enthalpies of Formation of Solid Alloys
Kubaschewski and co-workers [60Kub] used direct reaction calorimetry, optical
metallography and X-ray diffraction to study 50 Ti-Al-V alloy compositions. Measured
enthalpies for solid alloy formation were reported for ten constant vanadium sections.
All of these data were used in the assessment. Figures 10-13 compare the calculated
enthalpy curves with the experimental data for constant vanadium contents of 5, 10, 15
and 20 at%.
2.3 A2-B2 Boundaries
Figure 14 shows the A2-B2 boundaries from 1573K to 873 calculated with the present
dataset. The B2 boundaries are in good agreement with the experimental data given by
Ahmed and Flower [94Ahml].
2.4 Liquidus Projection
Figure 15 gives the calculated liquidus projection. The sequence and positions of the
invariant reactions are in broad agreement with the available experimental results
[94Ahm2, 91 Par].
3 Conclusions
The present dataset give calculated phase equilibria which show good agreement with
the experimental data over a wide range of temperature ie from 1573K to 873K. The
dataset is consistent with the calorimetrie values for the enthalpies of formation of the
solid alloys for alloys containing > 50 at% Ti. Towards the Al-rich coiner however the
agreement with the experimental data points is poor. For all of the sections studied the
Al-rich phases have lower heats than given by the dataset.
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