In recent years the Co–Cr system attracted much attention. There exist at least three published computer assessments of the system [1997Kus, 1998Hav, 2002Oik].
All the listed calculations seem to be based mainly on experimental data as on phase equilibria. Enthalpies derived from excess Gibbs energies as obtained by [1998Hav] were preferred to calorymetric data of [1977Kub]. Moreover, the former indeed were not directly measured but are results of model treatment of measured ratio of vapor pressures of both components. In the calculation performed with participation of one of present authors [2001Kab] more attention was paid to calorimetric measurements [1973Bel, 1977Kub].
All the calculations [1997Kus, 1998Hav, 2001Kab, 2002Oik] ignored e.m.f. data of [1973Bel] though e.m.f. values are usually considered to be more accurate then data of vapor pressures, which were accounted for [1998Hav, 2002Oik].
The temperature dependencies of the e.m.f. data were used to obtain both the temperatures of FCC→FCC+HCP boundary and corresponding discontinuity of partial entropies and enthalpies of Cr. These data in turn enabled us to calculate the values of stability function near that phase transition. Calculations were performed in frame of analytical thermodynamics and are model free. The values of stability function were obtained for f.c.c. phase at two points on aforementioned boundary: xCr = 0.15, 1092 K and xCr = 0.276, 1230 K.
Being second concentration derivative of Gibbs energy, the stability function is to be more sensitive than either integral or partial functions. So that values of stability function were used as extra test of computer assessments of the system [1997Kus, 1998Hav, 2001Kab, 2002Oik].
Neither calculation gave quite satisfactory agreement. The results of [2001Kab] are close to experimental value at 1230 K, whereas at 1092 K best agreement was achieved by [2002Oik]. Taking into account imperfect agreement of [1997Kus], [1998Hav] and [2002Oik] with experimental thermodynamic data and of [2001Kab] with detailed position of phase boundaries, new calculations aimed to achieve better coupling of all the thermochemical data and phase equilibria in the Co–Cr system still remain necessary.
The work is part of a research projects under the terms RFBR N 02-03-32621 and grant B0056 of the Russian Federation Target Program “Integration”.
[1973Bel] Bell, H.B., Hajra, J.P., Putland, F.P. Kubaschewski, O., Metal Sci. J., 7, 185–190 (1973)
[1977Kub] Kubaschewski, O., Grundmann, J., Ber. Bunsenges. Phys. Chem, 81, 1239–1242 (1977)
[1997Kus] Kussovski, A., Jansson, B., CALPHAD, 21, 321–333 (1997)
[1998Hav] Havrankova, J., Vrestal, J., Tomishka, J., Ber. Bunsenges. Phys. Chem., 102, 1225–1230
(1998)
[2001Kab] Kabanova, E.G., Kuznetsov, V.N., Zhmurko, G.P., Guzei, L.S., 6th International School-
Conference “Phase Diagrams in Materials Science” [Abstracts], Kiev, 2001, 196–197
[2002Oik] Oikawa K., Quin, Gao-Wu, Ikeshoi, T., Kainuma, R., Ishida, K., Acta Mater., 50, 2223–2232
(2002)