Study of phase equilibria in the Al - Pd - Re system

Scanning and transmission electron microscopy have been combined with x-ray diffraction to examine the phase equilibria in the Al - Pd - Re system at 1000°C for compositions from 50 to 100 at.% Al, and the corresponding isothermal section has been constructed. The binary monoclinic Al₃Re phase has been observed for the first time. It is confirmed that there is a stable icosahedral phase in this system. The boundaries to its homogeneity region have been determined and the phase equilibria in which it participates.     

Phase equilibria in the Ni-Al-Ti system at 1173 k

The phase equilibria at 1173 K have been determined in the Ni-AI-Ti system for Al contents less than 50 at. pct. The extent of theH (Ni₂AlTi) phase field has been established as well as the extent of solubility in the binary compounds γ (Ni₃Al), ν(Ni₃Ti), β₂(NiTi), NiTi₂, and ζ(AlTi₃). Substantial differences were found between the phase equilibria determined in this study and previous studies, in part due to the large solubility of Al in NiTi₂.     

Phase Equilibria in the Melting - Crystallization Region for Alloys in the Ti - TiNi - Sc0.53Ni0.47 - Sc Subsystem

Physicochemical analysis methods have been applied to the phase equilibria in the Ti - TiNi - Sc_0.53Ni_0.47 - Sc subsystem of the Ti - Ni - Sc ternary system. No ternary compounds are found in the subsystem. Isomorphous phases based on Ti₂Ni and Sc_0.72Ni_0.28 form continuous series of solid solutions (η) at subsolidus temperatures, as do the equiatomic compounds TiNi and Sc_0.53Ni_0.47. The crystallization of the η phase in the ternary system is incongruent, as in the binary systems Ti - Ni and Sc - Ni. The solidus surface for the Ti - TiNi - Sc_0.53Ni_0.47 - Sc subsystem has a nonvariant four-phase reaction of transition type at 830 °C. The compositions of the alloys that take part in it extend to the Sc - Ni side.     

The Cr−Re phase diagram

The phase diagram for the Cr−Re system has been derived from published data in conjunction with measurements on alloys cast and annealed at subsolidus temperatures (XRD, metallography, microprobe analysis, and measurement of the temperature for the onset of melting by the Pirani—Alterthum method). The phase equilibria at solidus temperatures have been determined from studies on alloys annealed at those temperatures. Phase homogeneity regions on the solidus have been identified: for (Cr) up to 43 at.% Re, for the σ phase −50–72 at.%Re, and for (Re) up to 17 at.%Cr; temperatures have also been determined for the invariant equilibria L+σ ⇆ (Cr) at 2150±15°C and L+(Re)⇆σ at 2335±15°C. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 3–4(406), pp. 65–71, March–April, 1999.     

Effect of Rhenium on Formation of the Structure of Eutectic Alloys Based on β-NiAl + γ-Re

We have studied phase equilibria and plotted the partial phase equilibria diagram for Ni Al Re in the region of compositions ranging from 0.2 to 14 at.% rhenium. We have established the dependence of the structure and the phase composition of the alloys in the Ni Al Re system on the rhenium concentration. We have determined the optimal ratio of the components at which the alloys have the maximum melting point. We have shown that the structure of the alloys is a composite consisting of a NiAl-based matrix and -Re fibers.     

Section of the isothermal tetrahedron of the Al-Cu-Mg-Zr phase diagram at 490°C

The phase equilibria in the Al-Cu-Mg-Zr system at 490°C have been studied for Al-rich alloys with 0.3% Zr and from 0 to 10% Cu or Mg. The (Al) solid solution is found to be in equilibrium with only binary θ(CuAl₂) and ZrAl₃ and ternary S (CuMgAl₂) phases of the ternary Al-Cu-Mg system. The section of the isothermal tetrahedron of the Al-Cu-Mg-Zr phase diagram at 490°C, which corresponds to 0.3% Zr and up to 10% Cu or Mg, is constructed.     

Phase Equilibria in the Ternary Al–Ti–Pt System. I. Solidus Surface of the Al–Ti–Pt System in the Range 0–50 at.% Pt

Powder Metallurgy and Metal Ceramics - The nature of phase equilibria has been examined for the first time in the Al–Ti–Pt system in the range 0–50 at.% Pt at subsolidus...     

Phase Equilibria in the Pr - Re - B System

X-ray diffraction methods have been applied to the component interaction in the system Pr - Re - B. Isothermal sections of the phase diagram have been constructed for 600°C (region of more than 33 at.% Pr) and 800°C (region less than 33 at.% Pr). The previously known borides Pr₂Re₃B₆, Pr₈Re_13–x B₁₂, Pr₇(Re₄B₄)₆ are confirmed, which have specific structural types. A new ternary compound has been found, Pr₃ReB₆ (structure not determined).__________Translated from Poroshkovaya Metallurgiya, Nos. 1–2(441), pp. 46–51, January–February, 2005.     

A New Rhombic Approximant in the Al - Pd - Fe System

Scanning and transmission electron microscopy have been used along with x-ray diffraction in the Al - Pd - Fe system to establish a new type of B-centered rhombic N phase. The lattice constants of the N phase are as follows: a = 2.31 nm, b = 1.60 nm, and c = 4.70 nm. Electron-probe microanalysis establishes the composition: Al_76.6Pd_10.0Fe_13.4. Differential thermal analysis indicates that the N phase melts incongruently at a temperature close to 885°C. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(443), pp. 94–99, May–June, 2005.     

Phase diagram of the Al2O3 - ZrO2 - Nd2O3 system. III. Solidus surface and phase equilibria in alloy crystallization

A projection has been constructed for the solidus surface in the Al₂O₃ - ZrO₂ - Nd₂O₃ phase diagram on the plane of the concentration triangle, which consists of six isothermal three-phase fields corresponding to two nonvariant equilibria of eutectic type and four nonvariant ones of peritectic type, together with five lineated surfaces for the end of crystallization of the monovariant eutectics. The highest solidus temperature in the system is 2710°C, the melting point of pure ZrO₂ , and the least is 1675°C, the temperature of the ternary eutectic L ? β + F + NA. No ternary phases and no appreciable regions of solid solutions based on their components and the binary compounds have been observed. Data on the adjoining binary systems, liquidus and solidus surfaces allowed for construction of the phase equilibrium diagram together with a reaction scheme for the equilibrium crystallization of alloys in the Al₂O₃ - ZrO₂ - Nd₂O₃ system.     

Effect of coherency stresses on α + α2 phase equilibria in TiAl alloys

Experiments were performed on two TiAl alloys to examine recent theoretical predictions concerning the characteristics of coherent two-phase equilibria in binary alloys. Equilibrium phase compositions in both the coherent and incoherent α + α₂ states at 725 and 800°C were determined by analytical electron microscopy. The results provide experimental evidence for the following predictions: (1) tie-line ends (equilibrium phase compositions) need not coincide with phase boundaries in the temperature-composition phase diagram and (2) the tie-line ends change with alloy composition at constant temperature. The experimental results have been compared with theoretical calculations of α + α₂ phase equilibria incorporating both elastic and ordering effects.     

Phase Equilibria in the TiO2-Rich Part of the TiO2-CaO-SiO2-10 Wt Pct Al2O3-5 Wt Pct MgO System at 1773 K

Metallurgical and Materials Transactions B - The phase equilibria of the TiO2-CaO-SiO2-10 wt pct Al2O3-5 wt pct MgO system in the TiO2-rich part were...     

Miscibility gap due to ordering in the BCC Fe-Ge system

Phase equilibria in the bcc Fe-Ge system have been investigated by means of electron probe microanalysis and transmission electron microscopy. Two kinds of ordered phases, B2 and DO₃ types, have been detected, the B2 phase being formed from the disordered A2 phase by a 2nd order transition. The DO₃ phase is also formed from the B2 phase by a 2nd or higher order transition at higher temperatures. Below about 820 °C, however, the transition becomes a 1st order, and a miscibility gap between these ordered phases occurs in the composition range from 13 to 16 at. pct Ge. It has been also confirmed that the solubility of Ge in the bec phase shows a retrogression due to the formation of DO₃ phase. On the basis of these experimental results, the phase diagram for the Fe-Ge system has been partly revised.     

Miscibility gap due to ordering in the BCC Fe-Ge system

Phase equilibria in the bcc Fe-Ge system have been investigated by means of electron probe microanalysis and transmission electron microscopy. Two kinds of ordered phases, B2 and DO₃ types, have been detected, the B2 phase being formed from the disordered A2 phase by a 2nd order transition. The DO₃ phase is also formed from the B2 phase by a 2nd or higher order transition at higher temperatures. Below about 820 °C, however, the transition becomes a 1st order, and a miscibility gap between these ordered phases occurs in the composition range from 13 to 16 at. pct Ge. It has been also confirmed that the solubility of Ge in the bec phase shows a retrogression due to the formation of DO₃ phase. On the basis of these experimental results, the phase diagram for the Fe-Ge system has been partly revised.     

Phase equilibria of the Na2O–SiO2 system between 1173 and 1873 K

Knowledge of phase equilibria in the Na₂O–SiO₂ system at elevated temperatures is important for mastering the metallurgical process and for the glass and ceramic industries. The phase diagram at metasilicate and silica saturations in the Na₂O–SiO₂ system between 1173 and 1873?K has been investigated by quenching and phase analyses. The experimental technique involved equilibration of high purity oxide mixtures at sub-liquidus temperatures, rapid quenching in cold water and followed by compositional measurement of the phases using electron probe X-ray microanalyser. The phases stable in the equilibrium assemblages have been characterised over a wide range of compositions and temperatures. The results were compared with previous experimental data and an optimised phase diagram.     

Directional solidification and phase equilibria in the Ni-Al system

A method for the optimization of a phase diagram on the basis of results from directional solidification experiments is proposed. The experimental microstructure selection map is compared with a calculated map and the input parameters are varied until a satisfactory agreement is obtained. The calculation of the microstructure selection map is based on the maximum temperature criterion and on analytical models for the growth of plane front, dendritic, and eutectic structures. This method is applied to the Ni-Al system where the phase equilibria close to the melting point of the γ′-Ni₃Al phase have been subject to discussion for over 50 years. A new version of this part of the phase diagram is proposed, which is coherent with the results from directional solidification experiments.     

Experimental investigation and thermodynamic calculation of the phase equilibria in the Cu-Sn and Cu-Sn-Mn systems

The phase equilibria in the Cu-rich portion of the Cu-Sn binary and Cu-Sn-Mn ternary systems have been determined using the diffusion-couple method, differential scanning calorimetry (DSC), high-temperature electron diffraction (HTED), and high-temperature X-ray diffraction (HTXRD) techniques. The present experimental results on the binary Cu-Sn system show the presence of the two-stage, second-order reaction A2 → B2 → D0₃ in the bcc-phase region, rather than a two-phase equilibrium between the disordered bcc (A2) and the ordered bcc (D0₃) phases, as reported before. Phase equilibria in the Cu-Sn-Mn ternary system in the composition range of 0 to 30 at. pct Sn and 0 to 30 at. pct Mn at 550 °C, 600 °C, 650 °C, and 700 °C have been determined, and a ternary compound (Cu₄MnSn) with a very small solubility has been detected. A thermodynamic analysis of the Cu-Sn-Mn ternary system including the Cu-Sn and Mn-Sn binary systems has also been carried out by the CALPHAD (Calculation of Phase Diagrams) method, in which the Gibbs energy of the bcc phase is described by the two-sublattice model in order to take into account the second-order A2/B2 ordering reaction. A consistent set of optimized thermodynamic parameters for the Cu-Sn-Mn system for describing the Gibbs energy of each phase results in a better fit between calculation and experiment.     

Interactions in the Ca2SiO4-CaZrO3 system

X-ray analysis at 20–1200°C and differential thermal analysis have been used to refine the transformation temperatures and unit-cell parameters for crystalline modifications of dicalcium silicate. Phase equilibria have been identified in the Ca₂SiO₄-CaZrO₃ system at 1100–2500°C. The phase diagram for this system has been derived. The characteristic features are the eutectic form for the liquidus and the formation of narrow solid-solution regions based on various crystalline modifications of Ca₂SiO₄.