Calculation of superalloy phase diagrams: Part IV
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HE previous papers in this series' -3 have demonstrated the means by which explicit descriptions of binary metallic systems can be employed to predict ternary systems. These papers, as well as previous studies 4-10 carried out along similar lines, have been used to generate a data base for describing the binary systems formed from ten technologically important metals: iron, chromium, nickel, cobalt, titanium, aluminum, carbon, niobium, molybdenum and tungsten. These metals combine to form forty-five binary systems and 120 ternary systems. In the present paper the five binary systems which have not yet been analyzed are considered, completing the set. Subsequently, isothermal sections in nine ternary systems are computed for comparison with limited experimental sections in these systems. As before, the description of ternary solutions is synthesized directly from the binary data without any additional information using Koehler's Equation. 1 -3 '' -9 No ternary terms are added! Finally the effects of carbon impurities on miscibility gap formation in several binary and ternary systems are discussed in the light of the thermochemical description of this set of systems.
with interaction parameters of 4250 and 2315 cal/g.at. respectively. A value for the liquid phase was not given; however, if the liquid phase is also considered to be regular, then the bcc parameter of 4250 and the observed phase diagram lo -12 require that the liquid be ideal. If these values are used to compute the entire phase diagram, it is found that the BCC/LIQUID equilibrium is correctly predicted for iron rich compositions. However, the BCC/LIQUID equilibrium in molybdenum rich solutions is not calculated correctly. Thus (with reference to Fig. 1) an ideal liquid and a regular bcc solution with an interaction parameter of 4250 cal/ g.at. results in a molybdenum-based bcc solution phase at 1820 K which is more extensive than observed. This discrepancy was of little consequence in the KirchnerHarvig-Uhrenius analysis -8 where attention was foT° K 1410 ° K (0.0157-0.0225) 2400
LIQUID 1820
1600
1. ANALYSES OF THE Fe -Mo, Fe-W AND Fe-Nb SYSTEMS
FCC
The current description of the iron-molybdenum, iron-tungsten and iron-niobium systems is displayed in Figs. 1 to 3 and Tables I to III in keeping with the available thermochemical and phase diagram data. 11 -17 The convention employed in tabulating solution and compound phase parameters is identical to that employed in previous papers in this series. 1 -3 Lattice stability values are identical with those employed earlier. 4 ' 7 The starting point for the analyses of the FeMo and Fe-W systems was the excellent theoretical and experimental study of the iron rich corner of the Fe -Mo, Fe-W and Fe -Mo -W systems at temperatures between 1000 K and 1900 K by Kirchner, Harvig and Uhrenius. 18 Kirchner et aí. 18 characterized the fcc, bcc and liquid phases in these systems in addition to treating the compounds Feo.600W0.400, Fe0.600Mo0.400 , Feo.630W0.370 and Feo.630Mo0 370. For the Fe -Mo case the bcc an
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