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Amorphization behavior in equiatomic high entropy alloys has been investigated. Pseudo-binary FeCrNi-M-B alloys and true equiatomic high entropy compositions FeCrNi-M-Si (M = Co, Mn, Nb, Ti, Zr) have been synthesized using mechanical alloying. Formation of amorphous phase has been confirmed using X-ray diffraction analysis and transmission electron microscopy. All alloys containing Si showed significant amorphization. Fe80B20 is known to be a good glass former, but no amorphous phase was observed in Fe-B based alloys except for FeCrNiNbB. The slower kinetics of dissolution of B in the alloy due to its sluggish diffusivity caused by its higher melting point is attributed to be the reason for the poor amorphization in B containing alloys. � 2015 Elsevier B.V.

Lead-free multiferroic ceramic composites of x Ni 0.93 Co 0.02 Mn 0.05 Fe 1.95 O 4 − (1– x ) Na 0.5 Bi 0.5 TiO 3 ( x NCMF − (1– x ) NBT, where x =0.1, 0.2, 0.3, 0.4 and 0.5 mol fraction) were synthesized by spark plasma sintering (SPS) in conjunction with high-energy ball milling. The phases, dielectric, piezoelectric, ferroelectric, magnetic and magnetoelectric properties of the composites were analyzed. The composites were composed of a mixture of spinel and perovskite phases. All the composite samples exhibited both apparent ferroelectric and ferromagnetic characteristics as well as considerable magnetoelectric (ME) effects. The maximum value of the ME voltage coefficient of the composites was quite high, being up to ~670 mV cm −1 Oe −1 for the 0.5 NCMF − 0.5 NBT composite. Overall, the synthesized composites were promising in terms of electrical, magnetic and magnetoelectric properties, indicating that the SPS is a promising method of fabricating ME composite materials.

High-entropy alloys (HEAs) have emerged as an important class of materials in the last one decade with immense potential both at the level of fundamental understanding and also in terms of applications. This chapter deals with the basic concepts that underpin this new class of alloys. It starts with the definition of HEAs and how they differ from other multicomponent alloys such as Ni-base superalloys. Then it gives a classification of alloys in terms of the number of components. A notation that is commonly used to represent composition in these alloys, particularly the nonequiatomic alloys with alloying additions, is brought out. Finally, four core effects of HEAs are elucidated, namely, high-entropy, severe lattice distortion, sluggish diffusion, and cocktail effects.

In recent years, there has been intense activity in the prediction of phases formed in high-entropy alloys through various means, and strategies based on integrated computational materials engineering (ICME) are taking prominent position in comparison to parametric approaches. While parametric approaches discussed in Chapter 3 are useful in rationalizing the phase obtained in high-entropy alloys and can also be useful in identifying the window of parameters that can lead to the formation of high-entropy alloys with a particular structure, the computational methods can be more predictive in nature. Among the computational approaches, the most prominent ones are CALPHAD method, ab-initio calculations, molecular dynamics and Monte Carlo simulations, and phase-field modeling. This chapter gives an account of the status of these approaches in the high-entropy alloys research.

While a number of equiatomic and nonequiatomic high-entropy alloys (HEAs) have shown a single solid solution, in a number of them various intermediate phases with the structure of intermetallic compounds such as B2, L12, sigma phase, and Laves phase are shown to occur. This has been attributed by many researchers to the competition among mixing entropy, mixing enthalpy, and atomic size difference between the constituent elements in these alloys. There are reports on high-entropy nitride and carbide formation as thin films on various substrates. These nitrides and carbides have the structure of interstitial compounds. There have been cases where HEA compositions have shown the formation of metallic glasses. Some of these alloys are equiatomic in nature, while some of them can be treated as pseudo-binary or pseudo-ternary with equiatomic substitution of similar elements. This chapter gives an account of intermetallic phases, interstitial alloys, and amorphous phases observed in HEAs.

The high mixing entropy of high-entropy alloys usually leads to the formation of disordered or partially ordered solid solutions in these alloys. It has been observed that disordered solid solution formation in such alloys happens, when elements with similar chemical nature and atomic size are chosen to form the alloys. If the constituent elements in these alloys have significant differences in terms of their atomic sizes or chemical nature, there is a tendency to form partially ordered solid solutions, or even stoichiometric compounds. Under certain conditions, amorphous phases might form. The present chapter attempts to rationalize these observations in terms of various approaches that were developed starting from the Hume-Rothery rules.

High-entropy alloys have been shown to have promising properties for a wide range of applications. For different applications, different critical properties are emphasized in the product design and materials selection. This chapter will focus on mechanical, wear, electrochemical, and oxidation properties, which are often basic or critical considerations for structural stability and lifetime in various applications. In the presentation of properties, alloy composition, processes, and microstructure are also correlated to give a better understanding on the phenomena and mechanisms. Based on this, it will be shown that there is a large space to further design composition and selection. There is scope to improve structural properties for specific purposes and applications.

High-entropy alloys (HEAs) are processed by a variety processing routes involving solid, liquid, and gaseous states. The most popular synthesis route for the HEAs is the melting and casting route through vacuum arc melting or induction melting followed by casting. There have been a few cases in which HEAs have been processed by directional solidification and Bridgman solidification. A large number of HEAs in recent years is being prepared by powder metallurgy route with mechanical alloying followed by consolidation with spark plasma sintering. This route ensures the formation of bulk nanocrystalline HEAs. In addition to the preparation of HEAs in bulk form, HEA coatings are also developed by a variety of techniques ranging from laser cladding to magnetron sputtering. Finally, combinatorial materials science is showing a lot of promise in developing new HEAs without the need for a large number of laborious experimentation.

High-entropy alloys (HEAs) concept has opened up an entirely new alloy field, which encompasses a wide range of microstructure and properties, and thus provides many opportunities to replace traditional materials and create new applications. This chapter will first overview the property goals pursued and advanced applications demanding new materials. Several application examples are described. The current state of both applied and granted patents related to HEAs are reviewed. In the end of this chapter, future directions of HEAs research and development will be pointed out including the fundamental and basic science, composites of HEAs with ceramic or high-entropy ceramic reinforcements, medium-entropy alloys, exploration of existing database for possible applications, new computational tools, integrating materials engineering, materials genome approach.

Alloys have helped and defined the march of civilization for over five millennia. The progress from native metals and native alloys to the accidental discovery of arsenical bronzes is a remarkable story. Numerous combinations of alloying elements were tried usually based on one principal element. Higher amounts of alloying were also used in alloys such as high-tin bronzes and ultrahigh carbon steels. From such concentrated binary alloys to multicomponent alloys marked a major advance resulting in alloy steels and superalloys in the last century. Nevertheless there was one element in major proportion in all these alloys. A revolutionary step in alloying occurred just before the beginning of the third millennium ce when Jien-Wei Yeh and Brian Cantor independently thought of multicomponent equiatomic or near-equiatomic alloys. Surprisingly, many of these alloys turned out to be solid solutions similar to the bronzes of the third millennium bce. They have breathed new life into materials world promising an extraordinarily rich family of alloys.

High-entropy alloys have promising functional properties for a wide range of applications. A number of functional properties could be required in different applications. In this chapter, we focus on some basic functional properties including diffusion barrier, electrical, thermal, magnetic, hydrogen storage, irradiation resistance, and catalytic properties. Properties, alloy composition, processes, crystal structure, and microstructure will be correlated to give a better understanding of the phenomena and mechanisms. It is found that further composition design and process selection are feasible to tune functional properties for specific purposes and applications. A few reports are also available on functional properties such as biomedical, antibacteria, EMI shielding, antifingerprint, antisticky, and hydrophilic and hydrophobic performances, which are not included in this chapter.

High-entropy alloys (HEAs), being multicomponent equiatomic or near equiatomic in nature, have a high mixing entropy. They have a strong tendency to form disordered and partially ordered solid solutions instead of stoichiometric intermetallic compounds or strong elemental segregation, when they are prepared through various processing routes. Most of the HEAs have FCC or BCC structures, while a few HEAs have shown the formation of HCP structures. Under certain conditions, when the interactions between some constituent elements differ a lot with others in nature, the formation of intermetallic compounds or elemental segregation has been observed because mixing entropy effect is not sufficient to mix them with larger mutual solubility. This chapter gives a comprehensive account of solid solution formation in HEAs.