https://dc.engconfintl.org/cgi/viewcontent.cgi?article=1032&context=superalloys_ii

A critical review of high entropy alloys and related concepts

Disordered multicomponent systems, occupying the mostly uncharted centres of phase diagrams, were proposed in 2004 as innovative materials with promising applications. The idea was to maximize the configurational entropy to stabilize (near) equimolar mixtures and achieve more robust systems, which became known as high-entropy materials. Initial research focused mainly on metal alloys and nitride films. In 2015, entropy stabilization was demonstrated in a mixture of oxides. Other high-entropy disordered ceramics rapidly followed, stimulating the addition of more components to obtain materials expressing a blend of properties, often highly enhanced. The systems were soon proven to be useful in wide-ranging technologies, including thermal barrier coatings, thermoelectrics, catalysts, batteries and wear-resistant and corrosion-resistant coatings. In this Review, we discuss the current state of the disordered ceramics field by examining the applications and the high-entropy features fuelling them, covering both theoretical predictions and experimental results. The influence of entropy is unavoidable and can no longer be ignored. In the space of ceramics, it leads to new materials that, both as bulk and thin films, will play important roles in technology in the decades to come. The valuable combination of disorder and non-metallic bonding gives rise to high-entropy ceramics. This Review explores the structures and chemistries of these versatile materials, and their applications in catalysis, water splitting, energy storage, thermoelectricity and thermal, environmental and wear protection.

High-entropy ceramics

High-entropy alloys (HEAs) are a relatively new class of materials that have gained considerable attention from the metallurgical research community over recent years They are characterised by their unconventional compositions, in that they are not based around a single major component, but rather comprise multiple principal alloying elements Four core effects have been proposed in HEAs: (1) the entropic stabilisation of solid solutions, (2) the severe distortion of their lattices, (3) sluggish diffusion kinetics and (4) that properties are derived from a cocktail effect By assessing these claims on the basis of existing experimental evidence in the literature, as well as classical metallurgical understanding, it is concluded that the significance of these effects may not be as great as initially believed The effect of entropic stabilisation does not appear to be overarching, insufficient evidence exists to establish the strain in the lattices of HEAs, and rapid precipitation observed in some HEAs sug

https://www.tandfonline.com/doi/pdf/10.1080/09506608.2016.1180020

High-entropy alloys: a critical assessment of their founding principles and future prospects

http://www.mmm.psu.edu/YWang2004ActaMater_NiAlThermodynamicProperties.pdf

Thermodynamic properties of Al, Ni, NiAl, and Ni3Al from first-principles calculations

The 𝜎 phase which exists in various series of stainless steels is a significant subject in steels science and engineering. The precipitation of the 𝜎 phase is also a widely discussed aspect of the science and technology of stainless steels. The microstructural variation, precipitation mechanism, prediction method, and effects of properties of 𝜎 phase are also of importance in academic discussions. In the first section, a brief introduction to the development and the precipitation characteristics (including morphologies and precipitation sites) of 𝜎 phase in stainless steels is presented. In the second section, the properties effect, prediction method, processing effect, elemental addition, retardation method and Thermo-Calc simulation of the 𝜎 phase in stainless steels are highlighted.

/pdf/overview-of-intermetallic-sigma-phase-precipitation-in-1d817vlxbh.pdf

Overview of Intermetallic Sigma () Phase Precipitation in Stainless Steels

Chapter headings: Introduction. History of CALPHAD. Basic Thermodynamics. Experimental Determination of Thermodynamic Quantities and Phase Diagrams. Thermodynamic Models for Solution and Compound Phases. Phase Stabilities. Ordering Models. The Role of Magnetic Gibbs Energy. Computational Methods. The Application of CALPHAD Methods. Combining Thermodynamics and Kinetics. Future Developments.

CALPHAD : calculation of phase diagrams : a comprehensive guide

This paper describes the recent development of models in JMatPro for the calculation of phase transformations and material properties that are critical to the prediction of distortion during the heat treatment of steels. The success of these models is based on the accurate description of all the major phase transformations taking place, including the formation of ferrite, pearlite, bainite and martensite, as well as the calculation of the properties of the different phases formed during the heat treatment process. One advantage of the current models is that they can be applied to many types of steels, including medium- to high-alloy types. A wide range of properties such as density, thermal expansion coefficient, thermal conductivity, strength and hardness can be calculated, all as a function of time, temperature and cooling rate, even for an arbitrary cooling profile. The material data calculated from JMatPro have been exported directly to Finite Element (FE)/Finite Difference(FD)-based packages for forging/deformation simulation.

Modelling phase transformations and material properties critical to the prediction of distortion during the heat treatment of steels

A full set of physical and thermophysical properties for lead-free solder (LFS) alloys have been calculated, including liquidus/solidus temperatures, fraction solid, density, coefficient of thermal expansion, thermal conductivity, Young’s modulus, viscosity, and liquid surface tension, all as a function of composition and temperature (extending into the liquid state). The results have been extensively validated against data available in the literature. A detailed comparison of the properties of two LFS alloys Sn-20In-2.8Ag and Sn-5.5Zn-4.5In-3.5Bi with Sn-37Pb has been made to show the utility and need for calculations that cover a wide range of properties, including the need to consider the effect of nonequilibrium cooling. The modeling of many of these properties follows well-established procedures previously used in JMatPro software for a range of structural alloys. This paper describes an additional procedure for the calculation of the liquid surface tension for multicomponent systems, based on the Butler equation. Future software developments are reviewed, including the addition of mechanical properties, but the present calculations can already make a useful contribution to the selection of appropriate new LFS alloys.

Modeling Material Properties of Lead-Free Solder Alloys

Premature fatigue fractures in structural components are a major problem in the manufacturing industry. The challenge for modellers has been to deliver reliable fatigue-analysis tools, because over-designing components is becoming an increasingly unattractive solution to the problem. Currently software packages exist for fatigue simulation of components or systems. However, a common feature of such software is that they all require the fatigue properties of the materials used. When such information is not available, the fatigue simulation cannot proceed until relevant experimental measurements are carried out, which can be both time-consuming and very costly. It is the aim of the current work to help solve this dilemma by developing models that can calculate the strain-life relationship not only at room temperature but also high temperatures. This work extends previous successful models for predicting the monotonic material properties of commercial alloys as a function of alloy chemistry, heat treatment, temperature and strain rate. In the present paper, attempts are made to model the high temperature fatigue properties of some engineering alloys. The effect of strain rate and cyclic loading frequency on fatigue properties are also discussed.© 2007 ASME

Modelling the Strain-Life Relationship of Commercial Alloys

Thedemandfornewandimproved lead-free solder (LFS) alloys growssteadily astheneedforreliable lead-free electronic products increases. Thermodynamic calculations haveproved tobeanimportant tool inproviding information forthedesign andunderstanding ofnew LFS systems. However, suchtools often fall short fromdirectly providing theinformation that isactually required bytheendusers, such asphysical andthermophysical properties. Inthepresent work, models havebeencreated suchthat afull setofsuch properties canbecalculated forsolder alloys forthemulticomponentsystemSn-Ag-Al-Au-Bi-Cu-In-Ni-Pb-Sb-Zn. Theproperties, given forboththeoverall alloy orforeach phaseifrequired, include coefficient ofthermal expansion, densities, various modulii, thermal conductivity, liquid surface tension andviscosity, all asafunction ofcomposition andtemperature (extending into theliquid state).

http://ieeexplore.ieee.org/iel5/4198846/4198847/04198936.pdf

Peter Miodownik

Papers

CALPHAD : calculation of phase diagrams : a comprehensive guide

Modelling phase transformations and material properties critical to the prediction of distortion during the heat treatment of steels

Modeling Material Properties of Lead-Free Solder Alloys

Modelling the Strain-Life Relationship of Commercial Alloys

Modelling ofThermodynamic, Thermophysical andPhysical Properties of Lead-Free Solder Alloys