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COST 507 - Repositório Aberto da Universidade do Porto

COST 507 - Repositório Aberto da Universidade do Porto

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Jonsson combined his descriptions of the Ti­C and Ti­N systems to describe the Ti­C­<br />

N [96cJon] system but had to introduce strong ternary interactions, in particular in the<br />

TiC­TiN section. Before a similar attempt was made, using the new assessment of the<br />

Ti­C system by Dumitrescu, an analysis was made of the information on the<br />

equilibrium between titanium carbonitrides of various compositions and liquid Fe<br />

[90Ozt]. It indicated that the interaction energy in the TiC­TiN section may be<br />

around ­18000 J/mol which is about one third of Jonsson's [96cJon] value. This new<br />

value was then used by Dumitrescu in an assessment of the Ti­C­N system, in<br />

combination with the new description of Ti­C. Jonsson's [96aJon] description of the<br />

Ti­N system was used. The result was rather satisfactory as demonstrated in Figs. 11,<br />

12, 13 and 14.<br />

5.2 The Al-Ti-C system<br />

It was pointed out by Seifert et al. [96Sei] that the experimental four­phase<br />

temperature for L + TiC + ALC 3 + Al 3 Ti in the Ti­Al­C system strongly favours the<br />

higher values of A f °H. It should be noticed that the use of this information<br />

depends on choices for A1 4 C 3 and Al 3 Ti. Several<br />

examined.<br />

alternatives should thus be<br />

The equilibrium temperature has been reported to be 1085 K which is not far from<br />

the melting point of Al. Thus, G m of pure liquid Al at this temperature is well<br />

established. The effect of Ti and C on G m of L is not very large because of the low<br />

contents of Ti and C. One can thus use any descriptions of the liquid phase in the Al­<br />

Ti and Al­C systems in a calculation of the four­phase equilibrium. G m of Al 3 Ti is<br />

obtained from assessing the ΑΙ­Ti system. There are two such assessments, by<br />

Saunders [94Sau] and by Zhang [96Zha]. We should thus use two values in our test.<br />

For ALtC 3 an older value was used by Gròbner et al. [95Grö] but recently Meschel<br />

[95Mes] gave a different value and Lukas [96Luk] modified the Al­C system<br />

description. For TiC Jonsson's [96bJon] description gave very low values and the<br />

experimental temperature thus gives strong preference for less negative value.<br />

Dumitrescu's value gave the following values<br />

[94Sau] + [96Luk]<br />

[94Sau] + [95Grö]<br />

[96Zha] +[96Luk]<br />

[96Zha] + [95Grö]<br />

908 K<br />

1061 K<br />

854 K<br />

1033 K<br />

These results give strong preference for the old value of A1 4 C 3 and some preference<br />

for Saunders' [94Sau] description of Al­Ti.<br />

5.3 The Ti-Ni-C system<br />

Schuster et al. [97Sch] have studied the solubility of TiC in fee Ni at equilibrium with<br />

graphite and compared with calculations and previous experiments. Experiments fell<br />

between calculated results based on Jonsson's , Fig.15, and Dumitrescu's values for<br />

TiC, Fig. 16. However, Schuster et al. used an assessment of Ni­Ti by Bellen [96Bel].<br />

­ 181 ­

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