Partial Liquidus Projection Research Articles

The MgO–TiO2–SiO2 system: Experiments and thermodynamic assessment

AbstractPhase relations in the MgO–TiO2–SiO2 system have been investigated in air over a wide temperature range using the equilibration method. X‐ray powder diffraction, scanning electron microscopy combined with wave length X‐ray spectroscopy (SEM/EPMA), and differential thermal analysis (DTA) have been used for sample characterization. Based on the obtained experimental results, isothermal sections of the system at 1523, 1673, and 1773 K have been established. The solid‐state invariant reaction MgTi2O5 + T‐SiO2⇋P‐MgSiO3 + TiO2 has been detected at 1625 ± 8 K by step‐wise heat treatment. A partial liquidus projection has been suggested, and the temperatures and compositions of three eutectic invariant reactions have been experimentally measured by DTA and ex‐situ analysis of the sample microstructures after melting using SEM/EPMA. Considering the newly obtained experimental data, thermodynamic parameters describing the system have been thermodynamically evaluated within the CALPHAD approach.

The partial liquidus projection and solidification sequences in Ti-(40–60) Al-(5–30) Nb alloys

The properties of Ti–Al–Nb alloys strongly depend on alloy compositions and microstructures. Proper design of these important aspects requires detailed knowledge of the solidification sequences and liquidus projection. However, there are still some conflicts between previous experimental and calculated results about the liquidus projections in the composition range of Ti-(40–60)Al-(5–30)Nb and this has hindered Ti–Al–Nb alloy development. In this present work, we explicitly investigated the as-cast microstructures and phase constitution of 50 alloys with the composition range of Ti-(40–60)Al-(5–30)Nb and clarified the solidification sequences. We re-constructed the partial liquidus projection and found that the primary β phase region extend to just below 55 at.% Al content and the primary α phase region extend to just below 24 at.% Nb content. Moreover, it was observed that the invariant reaction between Liquid, β, α and γ phases is a peritectic reaction (Liquid+β+γ→α) and all the Liquid+β+γ, Liquid+β+α and Liquid+α+γ three-phase regions are of peritectic type. The present work provides essential information necessary for optimizing the Ti–Al–Nb thermodynamic database to accelerate alloy development.

Experimental Investigations of the Fe-Mn-Ti System in the Concentration Range of up to 30\xa0at.% Ti

The ternary Fe-Mn-Ti system was investigated in the compositional range of up to 30 at.% Ti for temperatures ranging from 1000 °C to the melting temperature. Based on the metallographic investigation of as-cast alloys a partial liquidus projection was constructed, revealing large primary solidifying regions for the phases A1, A2, A12, A13, C14 and Mn4Ti. Isothermal heat treatments at 1000 and 1200 °C revealed wide homogeneity ranges for the Mn-based phases A12 and A13 at Ti contents between 5 and 20 at.% and up to 65 at.% of Fe, indicating an electron-mediated stabilization of both phases for the simultaneous solution of Fe and Ti.

Phase Equilibria in the Al-Co-Ni Alloy System

The phase equilibria in the Ni-Co rich region (<50 at.%Al) of the Al-Co-Ni system were studied experimentally for two isothermal sections at 1100 and 800 °C. Metallography, energy dispersive spectroscopy, hardness and x-ray diffraction were used for characterization and determination of γ, γ′ and β phases within the ternary system. Phase boundaries in the isothermal sections and a partial liquidus projection are modified compared to previously published work. Comparison is made to the isothermal sections computed using Thermo-Calc and the TCNI8 database. No definitive experimental evidence corroborating the predicted existence of a Nishizawa horn was obtained.

Solidification paths in the iron-rich part of the Fe–Ti–B ternary system

Iron-rich alloys in the Fe–Ti–B system are being studied for their potential as a new generation of lightened steel-matrix composites reinforced by titanium diborides. In this work, the iron-rich corner of the Fe–Ti–B ternary system was investigated at temperatures between 1150 °C and 1400 °C. For this purpose, fourteen key alloys containing up to 5 mass % Ti and B were selected on the basis of preliminary thermodynamic calculations and processed in an induction furnace by melting the starting materials at 1630 °C for 1 h. Two types of experiments were performed: (i) long-duration annealing experiments, involving a liquid phase, performed by the electromagnetic phase separation technique at temperatures between 1175 °C and 1250 °C and (ii) differential thermal analysis of samples during heating up to 1400 °C and cooling with different cooling and heating rates (2, 5 and 10 °C min−1).Samples were characterized by X-ray diffraction, scanning electron microscopy, field electron gun scanning electron microscopy and complementary chemical analysis, combining electron microprobe analysis, inductively coupled plasma and secondary ion mass spectrometry, were performed. On the basis of an analysis of the solidification paths of the fourteen alloys as well as solid/liquid equilibria investigations, a partial liquidus projection in the investigated region was proposed. Moreover, the composition and melting temperature of the γFe–TiB2–Fe2B ternary eutectic alloy are determined with good accuracy. This study is a first step towards an extended experimental work on the iron-rich corner of the Fe–Ti–B ternary system.

Al–Ge–Ti: Phase equilibria and structural characterization of new ternary compounds

Phase equilibria of Al–Ge–Ti have been investigated using scanning electron microscopy (SEM), powder X-ray diffraction (XRD) and differential thermal analysis (DTA). Partial isothermal sections at 400 °C, 520 °C and 1000 °C were obtained with focus on the titanium-poor part up to 50 at.% titanium. Three ternary compounds were found to exist. The compound Al3GeTi (τ1) crystallizes in an own structure type (P4/nmm, tP10). Two structurally closely related compounds were found at the composition Al1−xGe1+xTi: τ2 (0.61 ≤ x ≤ 0.73), Al4Si5Zr3-type, I41/amd, tI24 and τ2′ (0.36 ≤ x ≤ 0.57), Si2Zr-type, Cmcm, oC12. DTA data were used to construct a ternary reaction scheme (Scheil diagram) up to approximately 1300 °C, a partial liquidus projection and two vertical sections, at 10 at.% Ti and at a constant Al:Ti ratio of 1:1. A total number of 12 ternary invariant reactions were identified.

Phase equilibria in the system Au–Cu–Si and structural characterization of the new compound Au5±xCu2±xSi

The ternary Au–Cu–Si system was investigated by means of powder X-ray diffraction (XRD) for phase identification, scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX) for microstructures and chemical compositions, light optical microscopy (LOM), and differential thermal analysis (DTA) for the determination of thermal effects. Three isothermal sections were constructed at 250 °C, 400 °C and 650 °C. A new ternary compound τ, Au5±xCu2±xSi, was identified and its crystal structure was determined by means of single crystal X-ray diffraction. It adopts a new crystal structure type in space group Pnma, Pearson symbol oP32 and shows a composition range between Au5.6Cu1.4Si and Au4.4Cu2.6Si at 250 °C. Lattice parameters were found to vary between a = 9.64–9.50 Å, b = 7.61–7.64 Å and c = 6.90–6.89 Å from the Au-rich to the Au-poor composition limit. Three vertical sections, at 10 and 30 at.% Si and at 10 at.% Cu, were constructed based on DTA data and four invariant ternary phase reactions were identified. A partial ternary reaction scheme (Scheil diagram) and a partial liquidus projection are given.

Partial liquidus projection and vertical sections in the system Al–Fe–Si–Ti

The quaternary system Al–Fe–Si–Ti was characterized in the Fe-rich part for thermal reactions, which were studied by differential thermal analysis (DTA). As-cast alloys were investigated in order to gain additional information about primary crystallization fields. Three sections through the liquidus projection were constructed at 50, 60 and 70 at.% Fe, considering the experimental data and those from literature. In addition, five selected vertical sections are presented. The microstructures of selected as-cast alloys in the primary crystallization fields of the Laves phase Fe2Ti, the A2/B2 phase, FeSi and τ2 (FeSiTi) are discussed.

Al-Ni-Y (Aluminum-Nickel-Yttrium)

The investigation of this ternary system by [1968Ros] presented an isothermal section at 1000 C for Ni-rich alloys. Later studies by [1977Ryk] showed the existence of a number of ternary compounds in the Y-lean region at 800 C. Subsequently, [1992Gla1], [1992Gla2], and [1993Gla] reported the structural characteristics of three additional Al-rich ternary compounds. A partial liquidus projection and an isothermal section at 500 C for Al-rich alloys were determined by [2000Rag]. Recently, a thermodynamic description of this system was developed by [2009Gol], with emphasis on liquid-solid reactions.

Al-Cr-Nb (Aluminum-Chromium-Niobium)

The update of this ternary system by [2008Rag] presented an isothermal section at 1000 C from [2004Zha] and a partial liquidus projection in the Nb-poor region from [2006Sou]. Based on the recent experimental results of [2009Pry], a thermodynamic assessment of this system was carried out by [2010He], who computed isothermal sections at 1450, 1300, 1150 and 1000 C and compared them with the experimental data.

Experimental Investigation and Thermodynamic Modeling of Phase Equilibria in the Hf-Ti-Si System

ABSTRACTPhase equilibria in ternary Hf-Ti-Si alloys were studied in the as-solidified and heat treated conditions using scanning electron microscopy, x-ray diffraction, and electron beam microprobe analysis. Selected solid-solid phase equilibria at 1350°C and a partial liquidus projection of the Hf-Ti-Si system at the metal rich end of the phase diagram were established. These data were then used to develop a thermodynamic description of the Hf-Ti-Si system using the CALPHAD (CALculation of PHAse Diagram) approach. The calculated isothermal section at 1350°C and the liquidus projection can satisfactorily account for the available experimental phase equilibria data and solidification paths. Both the calculations and the experimental data suggested that the metal-rich end of the ternary phase diagram possesses one transition reaction: L + (Hf, Ti)5Si3 → Hf(Ti)2Si + β(Hf, Ti, Si).

Processing and Characterizing RuAl Eutectics

ABSTRACTEutectic alloys in the Ru-Al-Mo system were directionally solidified by a cold crucible Czochralski technique. The solidification microstructures and composition of the phases were examined and used to estimate a partial liquidus projection. Preliminary results from compression and hardness testing indicate that the hardness of RuAl varies significantly with composition. The Ru-rich alloys in which RuAl is in equilibrium with the hcp (Ru,Mo) solid solution were found to have the lowest hardness values.

The Reaction of 80 wt.% Au - 20 wt.% Sn Solder Alloy with Gallium

As part of an investigation of the problems sometimes encountered when soldering GaAs semiconductor devices with 80 wt.% Au - 20 wt.% Sn solder, the constitution of alloys containing up to 14.21 wt.% Ga have been determined by thermal analysis, metallographic and SEM examination. It is concluded that the high solubility of Ga in the liquid phase makes it unlikely that the Au layer normally present on the GaAs will be stable under typical soldering conditions. However, pre-saturating the solder with Ga may avoid this problem. The ternary data obtained, together with existing binary information, has been used to construct a provisional partial liquidus projection surface for the system.

Phase equilibria of the Ga–Ni–As ternary system

Phase equilibria were investigated in the Ga–Ni–As ternary system, with particular emphasis on the regions of technological importance to Ni/GaAs electrical contacts. A 600 °C Gibbs isotherm was constructed using x-ray-diffraction analysis and electron probe microanalysis of annealed samples. Additionally, three isopleths (NiAs–GaAs, NiGa–NiAs, and NiGa–GaAs) and a partial liquidus projection were established using differential thermal analysis and metallography. These data were utilized to clarify some discrepancies in the literature pertaining to the constitution of the Ga–Ni–As system, particularly questions about the existence of ternary phases. It was demonstrated that at 600 °C, previously reported ternary phases were actually specific compositions of the binary phase, NiAs, which exhibits significant ternary solubility. Additional x-ray-diffraction and differential thermal analysis experiments suggested that superlattice structures based on the NiAs structure may become stable at lower temperatures. A ternary eutectic reaction was shown to occur at 810±5 °C, with eutectic point at the composition Ni0.48Ga0.30As0.22. The existence of this eutectic reaction has important ramifications for the development of Ni-based electrical contacts to GaAs because any metallization scheme with a composition within the region bounded by NiGa, NiAs, and GaAs, as well as elemental Ni, will experience at least partial liquid formation at temperatures greater than 810 °C.

Liquidus projection of Ti–Al–Si ternary systemin vicinity of γ alloys

AbstractThe microstructure, nature, distribution, and chemical composition of the different phases obtained in γ-TiAl alloys with small amounts of silicon additions have been investigated. Based on the microstructures observed and results obtained via energy dispersive X -ray microanalysis, the approximate partial liquidus projection of the ternary Ti–Al–Si system in the range of compositions over which γ alloys exist, has been established. Two four phase invariant points on which peritectic reactions occur are present. The eutectic valley between β and Ti5 (Si, Al)3 phases exhibits a maximum point, and the liquidus surface in this region is of saddle type. The results were found to be in good agreement with predictions based on thermodynamic modelling.MST/1937

Cr-Fe-N (chromium-iron-nitrogen)

[87Rag] reviewed the experimental and computed Cr-Fe-N phase equilibria. The evaluated data were presented as: (1) a partial liquidus projection for Fe-rich alloys, (2) computed iso thermal sections for Fe-rich alloys at 1200 and 1000 °C, (3) experimental isothermal sections at 700 and 567 °C, and (4) a reaction scheme.

The development of a pseudoeutectic nickel-based composite alloy

This paper gives a detailed account of the development of a Ni-Cr-Be composite alloy. Its cast structure is that of a duplex eutectic with hard nickel beryllide fibers embedded in a softer Ni-Cr solid solution matrix. A partial liquidus projection of the Ni-Cr-Be system was determined in order to define the solidification conditions and optimum composition range for the alloy. Alloying with aluminum, tungsten, and molybdenum was used to enhance the mechanical properties of the material. Heat treatment conditions, mechanical properties, and oxidation behavior are presented.