Convenient methods of correlation and prediction of S+L diagrams exist only for systems forming eutectics. To deal with solid solutions, we have adopted the model of strictly regular solutions of Guggenheim [3–5]. Our key assumption is that values of the Gibbs function of interchange w are different in the two coexisting phases: wS and wL. The assumption is based on the fact that the average interatomic distances R are also different, and this affects the averages of the interatomic (or intermolecular) potentials. The input parameters are enthalpies and temperatures of melting of pure components and any pair of experimental points on the diagram. For a number of binary alloy systems the agreement with the experiment is good. Since we believe in the basic unity of materials (see Chap. 1 in [7]), calcuations have also been made for organic mixtures, again with good results.

During rapid solidification, the nucleation and/or growth of a thermodynamically stable phase may be difficult. In this case the liquidus, solidus or other thermodynamic data for a metastable phase are important for the interpretation and prediction of the phases present in rapidly solidified materials. In this paper various techniques are described to obtain information about metastable equilibrium from measured stable equilibrium data. Extrapolations of phase boundaries as functions of temperature, pressure or composition (including a new component) into regions of metastability can often be constructed directly on the equilibrium diagram. These constructions can be performed more quantitatively with analytical methods using thermodynamic modelling of the free energy functions consistent with measured data. A number of examples are considered including a discussion of metastable liquid miscibility gaps, metastable eutectic and peritectic reactions, pressure diagrams and metastability in ternary alloys to indicate the possible product phase selection. A coupling of metastable phase diagrams with a solidification kinetics analysis can contribute towards effective alloy design and processing during rapid solidification.

The notion that it should be possible to assess the glass forming ability (GFA) of a given alloy, or alloy system, is a well established concept. If crystallization in the liquid on cooling can be prevented relatively easily, making it possible for a liquid alloy to be cooled through the glass transition temperature (Tg), while employing only a relatively slow cooling rate, the GFA is said to be large. A numerical measure of GFA is frequently expressed in terms of the reduced glass temperature ratio Trg=Tg/Tl, where Tl is the equilibrium liquidus temperature [1]. While the role of Tg in this ratio is clear, the role of Tl is less obvious. Tl can be derived from the features of the phase diagram, but attempts have also been made to calculate Tl from the heats of fusion and the melting points of the constituents involved in a given alloy [2]. At the same time, however, it must be recognized that in a crystallization process under rapid cooling conditions both the temperature of solidification and the composition and structure of the crystalline phase, or phases, which compete with glass formation, are likely to be highly nonequilibrium. Even if a suitable adjustment of the Tl value is made to allow for these features, the Tl fails to take into account the kinetic aspects involved in the glass forming process. Yet these aspects undoubtedly also influence the GFA.

Stable and metastable equilibrium diagrams and To curves are calculated for the Al-based binary systems Al-Ga, Al-Ge, Al-Fe, Al-Mg, and Al-Si. Extended solid solubilities and metastable phases have been produced by rapid solidification for each of these systems, and the calculations are compared to experimental observations.

Knowledge of the metastable crystalline alloy phases that can be prepared from the liquid or vapor by non-equilibrium methods is useful because the descriptive crystal chemistry of an alloy system should include metastable phases stable with respect to the components but unstable respective to other intermediate phases [1]. Alloy phases within a certain range of positive free energy of formation are also of interest, especially for systems without equilibrium phases. Accordingly, there have been some systematic “hunts” for metastable alloy phases (MAP's) that can be prepared by rapid liquid quenching, reviewed in Refs. 2–7. The principal results of these studies on disordered (element-like) and ordered MAP's and some additional data are presented here.

Aluminum-rich Al-Fe binary alloys up to and including Al3Fe were prepared by melt spinning in order to study the metastable phase structure and its transformation following heat treatment. Transmission electron microscopy and nuclear gamma-ray resonance were utilized in the study. The rapidly solidified structure was found to contain up to three metastable phases. One of the phases, with a composition and a gamma-ray resonance spectrum appropriate for Al6Fe, has either a globular or a cellular morphology upon quenching.

The structure of a large ranqe of model steels and high speed steels after rapid solidification are described in terms of the effect of processing conditions and alloy content. General lessons are deduced for these structures regarding the stability of austenite, ferrite, ′ and ɛ martensite, and excess carbon concentrations in rapidly solidified steels and these are compared with other workers' results. Some preliminary data regarding the structure of model nickel alloys are presented in order to shed light on previously described structures of nickel superalloys.

The transition behavior of the amorphous Cu60Zr40 alloy system during its transition to crystallinity by thermal cycling has been studied. A Differential Scanning Calorimeter (Perkin-Elmer model DSC-2) was used to record, in situ, the onset of thermal evolution of the sample during the course of transition. Analysis of DSC tracings reveal that: a. Transition occurs at a lower temperature than those transformed without thermal cycling, b. The amplitude of the exothermic rise decreases proportionally with increasing numbers of the thermal cycles and c. Details of the profile of the DSC tracing, i.e., the width of the exothermic rise and the presence of the secondary exotherm, are quite different from those transformed without thermal cycling. Preliminary high resolution electron microscopy of thermally cycled samples indicate random distribution of copper-rich precipitates at the early stages of cycling and their coalescence during the final stage of crystallization. For large number of cycles, however, the induced strains from thermal cycles contributes to the image contrast of the quenched solid thus allowing the assessment of the proposed atomic level stresses and strains, via technique of high resolution electron microscopy.

The hydrogen solubility of glassy Pdl00-xSix alloys with 14≤x≤22 has been measured in the temperature range of 10°C to 90°C and the hydrogen partial pressure range of 0 to 100 torr. The absorption of hydrogen in these glassy alloys is exothermic and Sieverts' law is not observed. An isothermal-isobaric ternary phase diagram showing the change of hydrogen solubility with silicon concentration is given. A preliminary analysis suggests that the hydrogen solubility is related to the atomic structure of the metallic glasses.

The ability to predict ready glass formation (RGF) in binary alloy systems upon rapid cooling of the melt is of value both theoretically and practically. Two-dimensional maps show promise as a means of associating RGF with two system parameters which must have a combination of favorable values. In this paper, two types of glass formation diagrams are reviewed. One of these, the ΔH-r/R plot, is based on fundamental parameters which can, in principle, be derived from elemental quantities for each binary alloy system. The second type of diagram, the temperature-composition map, uses two equilibrium phase diagram features, namely reduced liquidus temperatures and reduced eutectic compositions to predict RGF. Both approaches are compared for binary alloys of Zr. The temperature-composition plot approach can be extended to predict qualitatively the RGF composition range of a given alloy system.

After a review of the historic development of the concept of paraequilibrium in the field of alloyed steels, the basic principles of restricted thermodynamic equilibrium at a migrating interface during phase transformations are outlined. As a demonstration they are first applied to classical nucleation. In addition to the case of paraequilibrium they are then applied to adiabatic and to isochoric conditions. It is argued that a full equilibrium model, with a spike of the intensive property in front of the migrating interface may be more realistic. It is shown that the full equilibrium conditions require about twice as much undercooling or underpressure as the restricted equilibrium conditions because of the consumption of driving force in the spike. The concept of restricted equilibrium only applies to heterogeneous phase transformations. For homogeneous reactions, the same experimental conditions will give full equilibrium.

In many solid-state phase changes, atoms in a crystal rearrange themselves to form several phases differing in composition and order, while retaining the topology of the original crystal [l]. Although the crystal is distorted, the individual sites that atoms occupy and the lattice can still be identified with equivalent positions in an undistorted crystal. An equilibrium with respect to atom rearrangement, keeping the crystal intact, is called a coherent equilibrium. Such an equilibrium has been observed and its properties can be computed [1–3]. Coherent equilibrium is usually compared with an incoherent phase equilibrium in which each of the same phases form separate crystals that do not interact elastically with the other phases, but exchange atoms. For large enough particles, coherent equilibrium is metastable with respect to incoherent equilibrium, and loss of coherency is a spontaneous process.

Ordering phenomena of adsorbed atoms that are commensurate with the substrate structure can be described by a two-dimensional lattice gas. The major features of temperature-coverage phase diagrams for commensurate overlayers are reviewed and illustrated with several experimental examples. For overlayers with net attractive interactions, a two-phase region consisting of ordered overlayer and nearly empty substrate surface forms at low coverage. Substrate extended defects such as steps can create diffusion barriers, thus forming thermodynamic subsystems by eliminating communication between adsorbed atoms on either side of the steps. Steps can also prevent the growth of a reconstructed layer. Experimental examples are presented.

The usefulness of the concept of an order parameter in describing phase transitions is discussed. Examples of order parameters are given in the context of broken symmetries, and defects in the order parameters are classified in terms of these symmetries.

Recent experiments on magnetically-ordered ternary and pseudoternary rare earth superconductors are briefly reviewed. Superconductivity has been found to coexist with antiferromagnetic order, but to be destroyed by the onset of ferromagnetic order at a second transition temperature Tc2∼TM, where TM is the Curie temperature. In antiferromagnetic superconductors, the antiferromagnetic order modifies superconducting properties such as the curve of the upper critical magnetic field versus temperature. In ferromagnetic superconductors, a long wavelength (∼ 102 Å sinusoidally modulated magnetic state develops in the superconducting state as a result of the superconducting-ferromagnetic interactions. The interplay of superconductivity and competing magnetic interactions in pseudoternary rare earth systems produces complex and interesting low temperature phase diagrams.

From magnetic measurements, the alloy Ni78Mn22 is found to undergo a field-induced transition from spin glassiness to ferromagnetism at a critical field that decreases from ∼140 Oe to zero as the temperature is raised from 4.2 K to 40 K, the ferromagnetic Curie point being ∼270 K. The alloy Ni74Mn26 is found to transform at 80 K from a spin glass to a state of infinite initial susceptibility but no spontaneous magnetization and to remain so up to 155 K, where it becomes paramagnetic. The spin-glass properties of Ni78Mn22 below 40 K and of Ni74Mn26 below 80 K include displaced hysteresis loops produced by cooling in a field. The changes in the hysteresis loops upon subsequent warming correspond to a gradual conversion of a unidirectional anisotropy to a uniaxial anisotropy.

In the temperature range between 1 mK and 3 mK and in magnetic fields between 0 T and 1 T, there are four distinct phases of liquid 3He and three distinct phases of solid 3He. The liquid becomes a triplet superfluid and the solid becomes a nuclear antiferromagnet. Despite the great differences which exist between a superfluid and an antiferromagnet, there are remarkable similarities between phase diagrams of the two systems.

The high intensity irradiation environments produced by advanced fast fission and proposed fusion reactors, high voltage electron microscopes, and heavy ion accelerators add a new and exciting dimension to materials science. Typical irradiations of alloys in these devices introduce the order of 108 J/mol displacement energy in the form of vacancy-interstitial (Frenkel) pairs. Although most of this energy is disspiated as heat during Frenkel pair recombination, significant amounts may be harnessed to produce microstructural change, hence changes in the phase diagram. This extended abstract discusses the various atomistic mechanisms available to convert irradiation energy to microstructural change and cites selected experimental observations where the various mechanisms are operative. An extensive, critical review of phase stability under irradiation is in press [1].

A feature of thin film reaction that is different from the reaction in bulk samples is the tendency to form a single intermetallic compound rather than all of them which are allowed according to the equilibrium phase diagram. For example, in thin film silicide formation, Pd2Si has been found to form alone and to grow as a layer between Pd and Si. The silicide is stable over a wide temperature range of 100 to 700°C. The phenomenon of single intermetallic compound growth is not unique to silicide formation between transition metal films and silicon, but is also commonly observed in reactions between bimetallic thin films. The phenomenon indicates phase stability.

Solids subjected to high velocity impact or explosive loading may undergo polymorphic phase transformation or melting within time periods appreciably less than 10-8s due to the intense shock-pressure environment. Although criteria for equilibrium phase transformation on the Hugoniot are satisfied, other nonequilibrium features unique to the shock-wave environment have been identified in the shock transformation process. These features include shear and heterogeneous deformation effects which control the transformation kinetics and microstructure of the transformed material. Transformation under shock loading leads to unusual microstructure in the recovered materials and can result in interesting and useful changes in physical and mechanical properties.