Phase constitution of some intermetallics in continuous quaternary pillar phase diagrams

In order to express multicomponent phase relationships, a new type of phase diagram, named a “pillar phase diagram,” is proposed. The pillar phase diagram is a sort of quaternary and Brewertype phase diagram. A pillar phase diagram at a temperature is easily constructed by (1) composing three sides of Brewer-type ternary-phase diagrams along the periodic table and (2) piling triangles of general ternary phase diagrams along the periodic table. Using the pillar phase diagrams, systematic understandings of phase constitution and stability along the periodic table can be performed for (1) binary intermetallics containing ternary and quaternary additional elements and (2) ternary intermetallics containing quaternary elements. Thus, the diagrams are convenient in terms of alloy design of multiphase intermetallic alloys. In this paper, the concept and the construction method of the pillar phase diagrams are described, and some examples are shown for systems related with L1₂ Ni₃Al, B2 NiAl, L2₁ Ni₂AlTi, B2 NiTi, B2 FeTi, L1₀ TiAl, and L1₂ Al₃Ti alloys.     

Practical applications of phase diagrams in continuous galvanizing

Zn-Fe based high-order phase diagrams have found a wide range of applications in continuous galvanizing. With the development of computer software DEAL (DetermineEffectiveALuminum), the Zn-rich corner of the Zn-Fe-Al phase diagram is being used daily for scientific interpretation of bath assays. Computer software PAL (PredictAluminumLevel), also developed by Teck Cominco Metals Ltd., assesses transient equilibria between the steel substrate and the liquid galvanizing alloy for the estimation of Fe dissolution and Al consumption in galvanizing. Aluminum deportment in galvanizing baths has been scientifically described based on the fact that bath assays corresponding to different locations and depths of a galvanizing bath formed one tie-line in the liquid-Fe₂Al₅ two-phase field of the Zn-Fe-Al phase diagram. Zn-Fe based high-order phase diagrams also afford a better understanding of the mechanisms for a number of industrial phenomena. These practical applications of the Zn-Fe based phase diagrams are detailed in the article. This article is based on a presentation made at the Galvanizers Association Ninety-Seventh Meeting held in Lexington, KY, from Oct 17 to 19, 2005.     

Phase equilibria and phase diagrams in carbide systems

Experimental data on phase equilibria in the Co-Ni-W-C, Fe-Ni-W-C, and Co-Ti-W-C systems are presented. This information includes the equilibria between the liquid phase at 1350 °C and tungsten carbide (WC) in the Fe-Ni-W-C system as well as the solubility of graphite in these liquids. Information on the solubility of graphite in the Co-Ni-W-C liquid is also presented. The majority of this information was used earlier for phase diagram evaluations by the ThermoCalc group at the Royal Institute of Technology in Stockhohn in collaboration with LTPCM-ENSEEG in Grenoble. Comparisons are made between calculated phase equilibria based on the results of their evaluations and the experimental phase equilibria. Heat treatments of Co-Ti-W-C alloys at 1100 °C resulted in the precipitation of a hexagonal tungsten-titanium carbide with a composition corresponding to the formula W₄Ti₂C_3-x:. To our knowledge, this carbide has not been mentioned in the literature. B. Uhrenius is now at AB Sandvik Hard Materials, S-126 80 Stockholm, Sweden. K. Forsén is now at Ericsson Oy, Helsinki, Finland. I. Andersson is now at Elektrokoppar AB, Helsingborg, Sweden.     

TerQuat: Approximate prediction of ternary and quaternary phase diagrams comprising stoichiometric phases

The TerQuat method is an easy-to-use tool for a first prediction of ternary and quaternary phase diagrams. A number of simplifications (only stoichiometric compounds; Δ_fG° can be approximated by the Miedema model, ΔH_Miedema, data) allows the user to get an impression of a ternary or quaternary system with only a minimum of knowledge about the system, namely a list of existing compounds. Stable tie lines are calculated by comparison of the Gibbs energy of reaction of all possible reactions between four phases in the ternary. In the quaternary system, all the competing two- and three-phase equilibria are compared with each other, and a list of stable equilibria is generated. In addition, the intersections of stable two- and three-phase equilibria with a user specified plane in the tetrahedron can be calculated and plotted. This enables a simple generation of a space model for the visualization of the quaternary system. This paper was presented at the International Phase Diagram Prediction Symposium sponsored by the ASM/MSD Thermodynamics and Phase Equilibria Committee at Materials Week, October 21-23,1991, in Cincinnati, Ohio. The symposium was organized by John Morral, University of Connecticut, and Philip Nash, Illinois Institute of Technology.     

Thermodynamic analysis of some binary phase diagrams involving liquid crystals

A computer-coupled thennodynamic/phase diagram analysis was performed on the phase diagram data of seven binary systems involving liquid crystals. These include five systems based on a homologous series of compounds and two others having 1:1 intermediate compounds. The excess Gibbs energies of the solution phases were thereby calculated, and evaluated phase diagrams were generated that are thermodynamically self-consistent. The results are discussed in the light of what is known about excess solution properties in such systems. The usefulness of the thermodynamic analysis is examined with respect to the prediction of the eutectics of ternary and higher order liquid crystal mixtures. The “Equal G Analysis” is also briefly discussed with reference to the estimation of the nonidealities of mesophase solutions.     

Thermodynamic analysis of some binary phase diagrams involving liquid crystals

A computer-coupled thennodynamic/phase diagram analysis was performed on the phase diagram data of seven binary systems involving liquid crystals. These include five systems based on a homologous series of compounds and two others having 1:1 intermediate compounds. The excess Gibbs energies of the solution phases were thereby calculated, and evaluated phase diagrams were generated that are thermodynamically self-consistent. The results are discussed in the light of what is known about excess solution properties in such systems. The usefulness of the thermodynamic analysis is examined with respect to the prediction of the eutectics of ternary and higher order liquid crystal mixtures. The “Equal G Analysis” is also briefly discussed with reference to the estimation of the nonidealities of mesophase solutions.     

Phase diagram study of Fe-Zn intermetallics

There are various intermetallic compounds in the Fe-Zn system. The phase diagram of this system is very important for understanding the surface structure of zinc-coated steel; therefore, equilibrium phases and their stable compositions must be known. The bulk samples of the Fe-Zn binary intermetallic compounds were synthesized by lengthy heat treatment for over 7.2×10⁵ s at 450 °C after 1.7×10⁵ s at 850 °C. The X-ray diffraction (XRD) patterns of samples kept for various periods at 450 °C were observed to determine the optimal heat treatment period, and the sample of Θ₁, which requires the longest time to form of all of the Fe-Zn binary intermetallic compounds, was obtained by the 7.2×10⁵ s heat treatment. Chemical composition of the samples was examined and X-ray diffraction was applied to ensure the formation of the intermetallic compounds. The results were in agreement with the literature on the Fe-Zn binary phase diagram.     

Phase diagram study of Fe-Zn intermetallics

There are various intermetallic compounds in the Fe-Zn system. The phase diagram of this system is very important for understanding the surface structure of zinc-coated steel; therefore, equilibrium phases and their stable compositions must be known. The bulk samples of the Fe-Zn binary intermetallic compounds were synthesized by lengthy heat treatment for over 7.2×10⁵ s at 450 °C after 1.7×10⁵ s at 850 °C. The X-ray diffraction (XRD) patterns of samples kept for various periods at 450 °C were observed to determine the optimal heat treatment period, and the sample of Θ₁, which requires the longest time to form of all of the Fe-Zn binary intermetallic compounds, was obtained by the 7.2×10⁵ s heat treatment. Chemical composition of the samples was examined and X-ray diffraction was applied to ensure the formation of the intermetallic compounds. The results were in agreement with the literature on the Fe-Zn binary phase diagram.     

The construction of isothermal quaternary phase diagrams of the Na-M-O-S type for hot corrosion applications

This paper presents a computer program for the calculation of the isothermal phase diagrams of quaternary systems involving sodium, a pure metal, oxygen and sulfur, which are useful for examining the experimental results concerning the hot corrosion of metallic materials. The procedures adopted to calculate the location of the points where four condensed phases are simultaneously present (quadruple points) and to draw the regions of stability of each phase containing the metal are presented by means of examples concerning a practical system. The nature of these quaternary phase diagrams is examined with reference to the various types of quadruple points and to their interconnections with lines of equilibrium involving the participation of three different phases. Examples of phase diagrams of some quaternary systems calculated by means of the present program are given.     

Gas phase aluminizing of TiAl intermetallics

The aim of this study was the microstructural characterization of aluminide diffusion coatings deposited on Ti48Al2Cr2Nb and Ti46Al7Nb alloys. The coatings' deposition process was prepared using out of pack method. The X-ray diffraction phase analysis from the surface of coatings indicated that TiAl₂ phase dominates in the coating. The thickness of aluminide coating was about 10 μm.     

Regions of incommensurability in phase diagrams

A discussion is given of the basic properties of incommensurate crystal phases and their occurrence in phase diagrams. The origin of the phenomenon is illustrated on a simple model that reproduces the main characteristics. The resulting model phase diagram and a number of phase diagrams of materials with an incommensurate phase are described.     

Computer representation of phase diagrams

The computer representation of phase diagrams is discussed from the point of view of user needs together with the form an ideal system might take for maximum utility. Current work in the field of computer representation of phase diagrams is reviewed and placed in the context of developing a more useful computerized alloy design system. Some new work on computerized interpolation of phase diagram data is also presented.     

Phase diagrams of nanometer-sized particles in binary systems

A study on alloy phase formation in nanometer-sized particles by insitu transmission-electron microscopy revealed that the phase equilibrium of these particles is significantly different from that of the corresponding bulk materials. A theoretical study was conducted based on thermodynamics modified so that Gibbs free energies for bulk materials available in the CALPHAD database were modified by taking into consideration factors affecting the phase equilibrium of nanometer-sized alloy particles. The study proved useful to evaluate the results obtained from experiments. For more information, contact Junggoo Lee, Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, Yamadaoka 2-1, Suita, Osaka 565-0871, Japan; +81-6-6879-7941; fax +81-6-6879-7942; e-mail; jg-lee@uhvem.osakau.ac.jp.     

Binary phase diagrams of transition elements

A brief explanation is given for the accompanying chart of binary phase diagrams of the transition elements together with references and a commentary on each reference.     

The practical use of phase diagrams

Phase diagrams are graphical representations of the states of equilibrium available to materials systems and the influence on the equilibrium states of changes in composition, temperature, and pressure. They are governed by the phase rule, which relates the number of degrees of freedom that an equilibrium has to the number of components and the number of phases occurring in the system. Phase equilibria in unary, binary, ternary, and quaternary systems are discussed, and phase and stability diagrams are applied to an understanding of vacuum sublimation, the removal of copper from liquid lead, the galvannealing of steel, tool steels, the production of Ti-B-C composites, stainless steels, the production of SiC and Si₄N₃, Al₂O₃-SiC composites, and processing of the superconducting oxide YBa₂Cu₃O_7-x.