Phase relationships in the neodymium-magnesium alloy system

The Nd-Mg system was studied using differential thermal analysis (DTA), X-ray examination, metallography, and microprobe analysis. The following intermetallic compounds were found to exist and their crystal structures confirmed or determined: NdMg (cubic, cP2 CsCl type, melting point 800 °C), NdMg₂ (cubic, cF24 MgCu₂ type, peritectic formation ∼755 °C), NdMg₃ (cubic, cF16 BiF₃ type, melting point 780 °C), and Nd₅Mg₄₁ (tetragonal, tI92 Ce₅Mg₄₁ type, decomposes peritectically at 560 °C). The NdMg₂ phase undergoes a eutectoidal decomposition at 660 °C. Three eutectic equilibria were observed to occur at 42.5 at. pct Mg and 775 °C, 64.5 at. pct Mg and 750 °C, and 92.5 at. pct Mg and 545 °C, respectively. In the Nd-rich alloys, previously determined data^[15] concerning the Mg solubility in α-Nd (8.2 at. pct Mg, ≈550 °C) were accepted. The Mg solubility in β-Nd was evaluated as 34 at. pct Mg at 775 °C. The β-Nd phase was observed to decompose eutectoidally at 17 at. pct Mg and 545 °C. Moreover, in the Mgrich alloys, a metastable NdMg₁₂ phase (tetragonal, tI26 ThMn₁₂ type) was observed in samples quenched from the liquid. The general properties of the Nd-Mg phases are compared with those of the R-Mg compounds and briefly discussed.     

Phase relationships and thermodynamic properties in the Mn-Ni-C system

In the present work, phase relationships in selected phase regions of the Mn-Ni-C system have been investigated at 1073 and 1223 K by use of an equilibration technique. Alloys of Mn-Ni-C were prepared from pure Mn, Ni, and C powders by the powder metallurgy method. The phase identification of the heat-treated samples was carried out by scanning electron microscope (SEM) and transmission electron microscope (TEM). The main phase compositions of the alloys have been analyzed by X-ray diffraction (XRD). The experimental results show that the site fraction of Ni in the metallic sublattice of the carbides M₂₃C₆, M₇C₃, and M₅C₂ is quite low and the value is around 0.02 to 0.03. The thermodynamic activities of manganese in 16 different Mn-Ni-C alloys have been studied by solid-state galvanic cell technique with single-crystal CaF₂ as the solid electrolyte in the temperature range 940 to 1165 K. The results are discussed in light of the available thermochemical information.     

Phase relationships in the fe-cr-mn-ni-c system at solidification temperatures

The phase relationships between the liquid phase and the primary solid phases were investigated in the iron-rich corner of the quinary system Fe-Cr-Mn-Ni-C. Of the five quaternary systems that comprise the quinary system, this study was limited to the three quaternary systems which contain both carbon and iron as two of the components;viz.: Fe-Cr-Mn-C, Fe-Cr-Ni-C, and Fe-Mn-Ni-C, as well as all of the binary and ternary subsystems that have iron as a component. This paper discusses the modeling efforts for these systems, with particular emphasis on the ternary systems Fe-Cr-Mn and Fe-Mn-Ni and the quaternary systems Fe-Cr-Mn-C and Fe-Mn-Ni-C. The experimental investigation consisted of measurements of tie-lines for the liquid-delta (bcc) and the liquid-gamma (fcc) equilibria in the iron-rich corner of the Gibbs simplex bounded by 0 to 25 wt pct Cr, 0 to 12 wt pct Mn, 0 to 25 wt pct Ni, and 0 to 1.2 wt pct C (bal. Fe). The temperature ranged from 1811 to about 1750 K. Compositions for the tie-lines were obtained from liquid-solid equilibrium couples, and the temperatures for the equilibrium by differential thermal analysis (DTA). Parameters were selected in a thermodynamic model of the alloy system to minimize the square of the difference between experimentally and calculated tie-lines, the latter being implicitly a function of the derived parameters in the model. Binary and higher-order parameters were generally required. Ternary parameters were obtained on ironcarbon base alloys Fe-Cr-C, Fe-Mn-C, and Fe-Ni-C, and for the Fe-Cr-Ni system, but not for the Fe-Cr-Mn and Fe-Mn-Ni systems. Of the quaternary systems investigated, quaternary parameters were required only for theL/δ equilibrium in the Fe-Cr-Ni-C system; the Fe-Cr-Mn-C and Fe-Mn-Ni-C systems were found to be represented adequately by employing only binary and ternary parameters.     

Phase relationships in the Fe-Cr-C system at solidification temperatures

The phase relationships between the liquid phase and the primary solid phases were investigated in the iron-rich corner of the Fe-Cr-C system. The investigation consisted of measurements of tie-lines and the liquidus surface of the liquid-delta (bcc) and liquid-gamma (fcc) equilibria in the Gibbs triangle, bounded by 0 to 1.4 wt pct C and 0 to 25 wt pct Cr (bal. Fe). The peritectic surface of the three-phase equilibrium was also measured. The temperature ranged from 1811 to about 1750 K. The tie-lines were obtained from liquid-solid equilibrium couples, and the liquidus and peritectic surfaces, by differential thermal analysis (DTA). A statistical procedure was applied to determine from the experimental results the parameters required for a thermodynamic model of the system. Calculations by the model are in good agreement with the experimental results. As a consequence the model can be used to interpolate and extrapolate properties and compositions of phases in equilibrium in the system within the composition and temperature field investigated. D.M. KUNDRAT, formerly Research Fellow at Massachusetts Institute of Technology M. CHOCHOL, formerly Research Assistant, Massachusetts Institute of Technology     

Phase relationships in the Fe-Cr-Ni system at solidification temperatures

The phase relationships between the liquid phase and the primary solid phases were investigated in the iron-rich corner of the Fe-Cr-Ni system as part of a larger study of the Fe-Cr-Ni-C system. The investigation consisted of measurements and modeling of tie-lines and the liquidus surfaces of the liquid-delta (bcc) and liquid-gamma (fcc) equilibria and the peritectic surface involving all three phases in the iron-rich corner of the Gibbs triangle bounded by 0 to 25 wt pct Cr and 0 to 25 wt pct Ni (bal Fe). The temperature ranged from the melting point of iron (1811 K) to about 1750 K. Compositions for tie-lines were obtained from liquid-solid equilibrium couples and temperatures for the surfaces were obtained by differential thermal analysis. Parameters for modeling the system were then selected in the subregular solution model to minimize the square of the difference between experimental and calculated tie-lines. With one ternary parameter employed for each phase, calculations by the model are in excellent agreement with the tie-line and liquidus measurements and in fair agreement with the temperatures for the peritectic surfaceL + δ/L + δ + γ. The usefulness of the model is demonstrated by calculation of the solidification paths of selected alloys in the composition field investigated for the limiting cases of (a) complete equilibrium followed by the alloy system, and (b) no solid diffusion (i.e., segregation) with equilibrium maintained at the solidifying front and complete mixing in the liquid phase.     

Phase relationships in the iron-rich Fe-Cr-Ni-C system at solidification temperatures

The phase relationships between the liquid phase and the primary solid phases were investigated in the iron-rich comer of the Fe-Cr-Ni-C system as part of a larger study of the Fe-Cr-Mn-Ni-C system. The investigation consisted of measurements of tie-lines for the liquid-delta (bcc) and the liquid-gamma (fcc) equilibria in the iron-rich corner of the Gibbs tetrahedron bounded by 0 to 25 wt Pct Cr, 0 to 25 wt Pct Ni, and 1.2 wt Pct C (bal. Fe). The temperature ranged from 1811 to 1750 K. Compositions for the tie-lines were obtained from liquid-solid equilibrium couples and the temperatures of the equilibrium, by differential thermal analysis (DTA). A mathematical procedure was employed on the experimental data to obtain parameters for a thermodynamic model of the alloy system. This involved minimization of an error function. The details of this analysis are discussed fully in this paper. Calculations by the model employing the “best-set” parameters are in good agreement with the experimental results. The usefulness of the model is demonstrated by calculation of the three-phase equilibrium in the quaternary system as a function of temperature. Formerly Research Fellow, Massachusetts Institute of Technology, is Senior Research Engineer, Armco Inc., Middletown, OH 45043     

Phase stability relationships and glass formation in the system Cu-Ag-In

Details are presented of phase relationships in the ternary system Cu-Ag-ln. Isothermal sections have been determined at 505 and 676 °C, and a most likely projected surface of primary crystallization is proposed. The phase relationships in this system are dominated by an extensive γ-phase (a Hume-Rothery “electron phase”) which extends approximately along a line of 30 at. pct In between the respective binary phases. The stability of the γ-phase follows approximately constant electron concentration lines and appears to be also enhanced by size relationships in the ternary system. The glassforming ability (GFA) in the Cu-Ag-ln system is poor, being limited to only a narrow region in the vicinity of alloy Cu₅₁Ag₃₁In₁₈. This behavior appears to be directly related to the stability of the γ-phase. An attempt has been made to interpret the GFA in terms of the most likely behavior of the T₀ surfaces.     

Phase relationships and thermodynamic properties of the Pd-S system

Sulfur pressures in the Pd-S system have been measured for liquid mattes and PdS/liquid matte mixtures by a Knudsen effusion technique, and for Pd/matte, Pd4S/matte, and Pd/Pd4S mixtures by an emf method employing a solid oxide electrolyte. The phase diagram has also been determined by conventional DTA methods from 0 to 50 at. pct sulfur, using microprobe analysis to confirm the identification of equilibrated phases. From this information, the standard free energies of formation of solid and liquid Pd₄S, Pd₃S, and Pd₁₆S₇ and solid PdS have been derived. For the reaction of solid Pd with S₂ gas to form solid sulfide, the values are ΔG°_TPd₄S = -184400 + 84.10T, ΔG°_TPd₃S =-172430 + 83.68T, ΔG°_TPd_16/7S = -182340 + 105.66T, and ΔG°_TPd_16/7S = -145180 + 88.12T, all in joules. The results for Pd₄S differ considerably from the previously accepted values.     

Microstructural characterization of rapidly solidified Al-Ta alloys

Two Al-rich Al-Ta alloys containing by weight 3 and 6 pct Ta have been rapidly solidified from the melt using the ‘gun’ technique. The microstructures and the crystal structures of the phases in the as-solidified as well as those formed on subsequent decomposition of the supersaturated solid solution have been characterized. A supersaturated solid solution was obtained in both the alloys in the as-solidified condition indicating a solid solubility extension of Ta in Al to almost 6 wt pct. The supersaturated solid solutions formed in both the alloys have been found to be quite stable up to 673 K (for 1 hour). Annealing at higher temperatures resulted in the formation of rod-shaped precipitates inside the grains and massive precipitates along grain boundaries. The rod-shaped precipitates arranged in a regular pattern constitute a new metastable intermediate phase Al₇Ta having an ordered structure. The massive precipitates which form along grain boundaries constitute the equilibrium Al₃Ta phase with a tetragonal crystal structure. The transformation behavior and the morphology of the transformation products are detailed in this paper.     

Phase relationships in the iron-rich Fe-Al alloys

X-ray diffraction study of isothermally annealed powder specimens of Fe-Al alloys with 18.75 to 32 at. pct Al indicates that the α + FeAl two-phase field closes at around 662‡C where both phases have the same composition: 23.9 at. pct Al. X-ray diffraction and magnetic data show that any twophase field that may exist between the FeAl and Fe₃Al phases must be extremely narrow. It is probable that there is no two-phase field and that the transition is of a higher than first order type.     

Phase equilibria in the system Fe-Mo-Cl-H-O

Conclusions Under the conditions we dealt with, only wQstlte is stable in the system Fe-Mo-O while molybdenum is reduced and passes into the solution. Practically with all compositions of the solid solution iron is predominantly chlorinated, and it passes into the molybdenum. Therefore the alloy iron-molybdenum can be obtained through the chloride phase only by chlorination of pure molybdenum. Chlorination of iron oxides and molybdenum oxides in the presence of hydrogen is inefficient because it is difficult to ensure the necessary composition of the gas phase.The results of the present work can be used for working out technological regimes of alloying the surface of iron objects through the chloride phase and for obtaining powdered alloys Iron-molybdenum.Translated from Poroshkovaya Metallurgiya, No. 1(301), pp. 43–46, January, 1988.     

Phase equilibria in the system molybdenum-chromium-carbon

Summary The methods of x-ray diffraction and microstructural analyses were employed for studying the system Mo-Cr-C, and an isothermal section (1350°C) of the system was plotted. At high carbon contents, the alloys which have not been subjected to heat-treatment contain, the-phase, which has a cubic face-centered structure of the NaCl type (a = 4.24–4.27 A). The carbide Mo₂C dissolves up to 46 at.% Cr, and the carbide Cr₂₃C₆ up to 15 at.% Mo. It is shown that the Mo atoms dissolved in the carbide Cr₂₃C₆ are distributed in an ordered manner.     

Phase equilibria in the Co-P-B system

Translated from Poroshkovaya Metallurgiya, No. 5(329), pp. 56–59, May, 1990.     

Phase equilibria in the system zirconium-chromium-carbon

Summary Phase equilibria in the system Zr-Cr-C at 1300°C were investigated by themethods of x-ray diffraction and microstructural analyses (Fig. 2). Zirconium carbide dissolves up to 6 at.% Cr, while chromium carbides dissolve negligible amounts of zirconium. In accordance with results of a thermodynamic calculation, zirconium carbide is in equilibrium with chromium carbides, chromium, and the compound ZrCr₂.     

Phase equilibria in the Al-Si-C system

The Al-C, Si-C, and Al-Si-C systems were investigated by metallography, X-ray diffraction, electron microprobe, and thermal analysis. Internally sealed liquidus crucibles were used to determine the solubility of C in Al and Si in the range 1700° to 2150 °C and isothermal sections for the ternary system at 2000° and 2150 °C. The isopleth Al₄C₃-SiC, determined in the range 1900° to 2300 °C, was found to contain the ternary intermediate phases 2A1₄C₃ · SiC and A1₄C₃ · SiC, which decompose incongruently at 2085° and 2080 °C, respectively. The incongruent decomposition temperature of A1₄C₃ (2156 °C) was confirmed. A phase reported by others with the stoichiometry Al₄C₃-2SiC was not confirmed. A partial liquidus surface was mapped from the carbon solubility and thermal analysis measurements.     

Phase equilibria in the system Zr-W-C

Summary The system Zr-W-C was investigated by the methods of X-ray diffraction and microstructural analyses. Phase equilibria at 1500°C were determined for as-cast and annealed alloys. The carbide ZrC dissolves 34 mo%WC at 500°C; at l,950°C. the solubility ofWC increases to 40 mol.'yo. As-cast alloys contain the - phase, which has a cubic NaCl-type structure (a = 4.25–4.30 A), and is distributed along the 50 at.% C line at 2–10 at.% Zr. It is shown that the solubility of WC in ZrC may be even greater at temperature approaching the melting point of the alloys.