Thermodynamic properties of B2-AlFeNi Alloys. Part I: Investigation by knudsen effusion mass spectrometry
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tion metal aluminides are of interest as high-temperature structural materials due to their very high melting temperatures, good oxidation resistance, and low mass density. A knowledge of their fundamental physical and chemical properties is a necessary prerequisite for the development of technical alloys. Our aim was to carry out systematic vaporization studies in order to measure activity data for all three components over sufficiently large ranges of temperature and composition in the B2 region of the Al-Fe-Ni system so that reliable partial and integral thermodynamic quantities could be derived. This appears to be the first time that measurements have been made for this phase by Knudsen effusion mass spectrometry (KEMS). Similar results for B2-AlFe and B2-AlNi, also studied by us, can be found in References 1 through 3, and a review of our earlier work on the nickel and titanium aluminides can be found in Reference 4. In these B2 near-triple defect transition metal aluminides, there are significant vacancy concentrations. The observed vacancy concentrations increase strongly in alloys containing more than 50 at. pct Al. At constant Al concentration and temperature, the B2-AlFe alloys have higher vacancy concentrations than found in B2-AlNi, while some ternary alloys have the highest concentrations of all.[5–10] The maximum vacancy concentraL. BENCZE, Professor, is with the Department of Physical Chemistry, Roland Eotvos University, 1117 Budapest, Hungary. T. MARKUS, Group Leader, and D. KATH, Engineer, are with Research Center Ju¨lich (KFA), Institute for Materials and Processes in Energy Systems (IWV-2), 52425 Ju¨lich, Germany. S. DASH, Scientific Officer, is with the Fuel Chemistry Division, Bhabha Atomic Research Center, Trombay, Mumbai 400085, India. D.D. RAJ, Scientific Officer, is with the Materials Chemistry Division, Indira Gandhi Centre for Atomic Research (GCAAR), Kalpakkam, 603102 Tamil Nadu, India. W.A. OATES, Professor, is with the Institute of Materials Research, University of Salford, Salford M5 4WT, United Kingdom. ¨ SER, Senior Scientist, is with IFW Dresden, D-01171 Dresden, W. LO Germany. K. HILPERT, Division Head, Research Center Ju¨lich (KFA), Institute for Materials and Processes in Energy Systems (IWV-2), is Professor, Technical University Darmstadt, Darmstadt, Germany 64289. Contact e-mail: [email protected] Manuscript submitted July 25, 2005. METALLURGICAL AND MATERIALS TRANSACTIONS A
tions observed, however, occur in B2-AlNi, this being because the phase boundary occurs at the highest Al concentrations in these alloys. An isothermal section at 1223 K of the phase diagram for the Al-Fe-Ni system is shown in Figure 1.[11] Our investigations were aimed at only alloys that lie within the B2 region of the system. For these chemically ternary alloys, only the integral thermodynamic properties of Al-Fe-Ni system have been determined previously. Zubkov et al.,[12] Gru¨n,[13] and Breuer et al.[14] used solution calorimetry, while Su et al.[15] used reaction calorimetry for the determination of the
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