THERMODYNAMIC PROPERTIES OF THE CR-AL AND V-AL SYSTEMS.
Final rept. 1 Mar 65-28 Feb 67,
NEW YORK UNIV N Y RESEARCH DIV
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The activity of aluminum in solid chromium-aluminum and vanadium aluminum alloys was determined between 15 and 80 at. Al in both systems, by an isopiestic method from specimens equilibrated at temperatures between 1170 and 1400K. Partial molar free energies, enthalpies and entropies and integral thermodynamic parameters were calculated at 1273K. In the Cr-Al system the departure of the activity of aluminum from ideal behavior is highly negative in the solid solution of Al in Cr and the high melting Cr5Al8 intermetallic compound. The entropy of mixing for the solid solution of Al in Cr is positive. A sharp change to a more negative integral entropy of mixing occurs for Cr5Al8, Cr4Al9 and CrAl4 intermetallic compounds, with a value of -1.54 e.u. at 80 at. Al. In addition, the integral free energy of mixing at 1273K reaches its largest value -5,900 calgr.-atom at 59 at. Al. The phase boundaries determined in this investigation disagree with those presented by Bradley and Lu, but are in substantial agreement with the work of Koester, Wachtel and Grube. The activity in the V-Al system also exhibits a marked negative deviation from ideality, with values close to that of the Cr-Al system. The phase boundaries obtained disagree with those presented by Hansen, but are in good agreement with those of Carlson, Kenney and Wilhelm. Author
- Properties of Metals and Alloys