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

A critical review of high entropy alloys and related concepts

Additive manufacturing (AM), widely known as 3D printing, is a method of manufacturing that forms parts from powder, wire or sheets in a process that proceeds layer by layer. Many techniques (using many different names) have been developed to accomplish this via melting or solid-state joining. In this review, these techniques for producing metal parts are explored, with a focus on the science of metal AM: processing defects, heat transfer, solidification, solid-state precipitation, mechanical properties and post-processing metallurgy. The various metal AM techniques are compared, with analysis of the strengths and limitations of each. Only a few alloys have been developed for commercial production, but recent efforts are presented as a path for the ongoing development of new materials for AM processes.

The metallurgy and processing science of metal additive manufacturing

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

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 article describes the development of a new multi-platform software program called JMatPro for calculating the properties and behavior of multi-component alloys. These properties are wide ranging, including thermophysical and physical properties (from room temperature to the liquid state), time-temperature-transformation/continuous-cooling transformation diagrams, stress/strain diagrams, proof and tensile stress, hardness, coarsening of γ′ and γ″, and creep. A feature of the new program is that the calculations are based on sound physical principles rather than purely statistical methods. Thus, many of the shortcomings of methods such as regression analysis can be overcome. With this program, sensitivity to microstructure can be included for many of the properties and the true inter-relationship between properties can be developed, for example in the modeling of creep and precipitation hardening.

Using JMatPro to model materials properties and behavior

Influence of stacking-fault energy on high temperature creep of alpha titanium alloys

This paper reviews the recent developments in material property modelling and its applications in processing simulation. Many material properties needed by process simulation can now be readily provided, such as the solidification properties and high temperature stress–strain curves. The solidification properties are affected by changes in composition within the specification range of an alloy; such changes in properties then affect casting simulation results. The mechanical properties are calculated by considering two competing deformation mechanisms (dominated by either dislocation glide or dislocation climb), with automatic selection of the dominant mechanism. Sample calculations are given for a variety of engineering alloys, including steels, aluminum, titanium, and nickel-based superalloys. The material properties data calculated can now be passed directly into commercial computer-aided engineering packages for casting and deformation simulation.

/pdf/material-properties-for-process-simulation-4krixezb6z.pdf

Material properties for process simulation

Thermo-physical and physical properties of liquid and solid phases during solidification are critical data for casting simulations. However, the number of alloys for which such information is available is limited, primarily due to the difficulty in experimentally determining these properties during the casting/solidification process. Because small variations in composition can have marked effects, it is unwise to extrapolate properties derived from other alloys. The purpose of this paper is to demonstrate the value of integrating the modelling of solidification and the associated thermo-physical and physical properties for multi-component alloys, using Java-based materials properties software (JMatPro). This includes how changes in the composition of an alloy within its specification range can substantially affect its properties during solidification and how properties of the liquid can vary significantly in the mushy zone.

http://www.thermotech.co.uk/resources/Casting-05.pdf

N. Saunders

Papers

CALPHAD : calculation of phase diagrams : a comprehensive guide

Using JMatPro to model materials properties and behavior

Influence of stacking-fault energy on high temperature creep of alpha titanium alloys

Material properties for process simulation

Modelling of materials properties and behaviour critical to casting simulation