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The effect of Mn on the activities of Fe, Ni, and Cr in an Fe-Ni-Cr base alloy.
Metall Trans, A, Phys Metall Mater Sci 1993 Nov; 24(11):2379-2382
A combination Knudsen cell-mass spectrometer apparatus developed by the Bureau of Mines is accurate enough to permit the activity of many alloy components to be measured directly as the ratio of the ion currents of an appropriate isotope evaporated from the alloy and from the pure component. This apparatus has been used to determine the activities of Fe, Ni, and Cr as functions of temperature in 71 Fe-20Ni-6Cr-3Mn (at. pct). A comparison of the data with data obtained earlier from other Fe-Ni-Cr base alloys indicates that partial substitution of Mn for Cr causes the activity coefficient of Fe to decrease and to deviate negatively above 1550 K. The activity coefficient of Ni is markedly increased by the substitution of Mn, and this increase is insensitive to temperature. In contrast, such a substitution decreases both the activity coefficient of Cr and the temperature dependence of this coefficient. The oxidation behavior of Fe-Ni-Cr base alloys, the stability of the austenitic phase in such alloys, and the Ni equivalent of Mn are discussed in light of these changes in activity coefficient.
Metallurgical-processes; Metallurgy; Iron-compounds; Nickel-compounds; Chromium-compounds
Metallurgical Transactions. A. Physical Metallurgy and Materials Science
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