Microstructure and Magnetic Properties of FeNiCuMnTiSnx High Entropy Alloys

FeNiCuMnTiSn_x multicomponent alloys (x = 0, 0.05, 0.1, 0.5, and 1 where x denotes the adding amount in atomic percentage when other elements are taken as 1) are prepared by an arc furnace. The results show that the crystal structure of FeNiCuMnTiSn_x alloys transforms from mixed intermetallic compounds to a single crystal structure (zinc blende structure) with the increasing of Sn content. The magnetization of the FeNiCuMnTiSn_x alloys gradually increases from 0.34 to 15.8 emu · g^?1 with the increasing x, the magnetic transformation undergoes from the paramagnetism (x = 0, 0.05, 0.1) to superparamagnetism (x = 0.5) finally to soft magnetism (x = 1) at room temperature. We use computer simulation and find that the magnetism of alloys appears when Fe atoms replace Ni atoms.     

High‐Entropy Alloys: Potential Candidates for High‐Temperature Applications – An Overview

Multi‐principal elemental alloys, commonly referred to as high‐entropy alloys (HEAs), are a new class of emerging advanced materials with novel alloy design concept. Unlike the design of conventional alloys, which is based on one or at most two principal elements, the design of HEA is based on multi‐principal elements in equal or near‐equal atomic ratio. The advent of HEA has revived the alloy design perception and paved the way to produce an ample number of compositions with different combinations of promising properties for a variety of structural applications. Among the properties possessed by HEAs, sluggish diffusion and strength retention at elevated temperature have caught wide attention. The need to develop new materials for high‐temperature applications with superior high‐temperature properties over superalloys has been one of the prime concerns of the high‐temperature materials research community. The current article shows that HEAs have the potential to replace Ni‐base superalloys as the next generation high‐temperature materials. This review focuses on the phase stability, microstructural stability, and high‐temperature mechanical properties of HEAs. This article will be highly beneficial for materials engineering and science community whose interest is in the development and understanding of HEAs for high‐temperature applications.     

Effect of Niobium on Microstructure and Properties of the CoCrFeNb_xNi High Entropy Alloys

A series of CoCrFeNb_xNi(x values in molar ratio, x = 0, 0.25, 0.45, 0.5, 0.75, 1.0 and 1.2) high entropy alloys(HEAs) was prepared to investigate the alloying effect of Nb on the microstructures and mechanical properties. The results indicate that the prepared CoCrFeNb_xNi(x 0) HEAs consist of a simple FCC solid solution phase and a Laves phase. The microstructures of the alloys change from an initial single-phase FCC solid solution structure(x = 0) to a hypoeutectic microstructure(x = 0.25), then to a full eutectic microstructure(x = 0.45) and finally to a hypereutectic microstructure(0.5 x 1.2). The compressive test results show that the Nb0.45(x = 0.45) alloy with a full eutectic microstructure possesses the highest compressive fracture strength of 2558 MPa and a fracture strain of 27.9%. The CoCrFeNi alloy exhibits an excellent compressive ductility, which can reach 50% height reduction without fracture. The Nb0.25 alloy with a hypoeutectic structure exhibits a larger plastic strain of 34.8%. With the increase of Nb content, increased hard/brittle Laves phase leads to a decrease of the plasticity and increases of the Vickers hardness and the wear resistance. The wear mass loss, width and depth of wear scar of the Nb1.2(x = 1.2) alloy with a hypereutectic structure are the lowest among all alloy systems, indicating that the wear resistance of the Nb1.2 alloy is the best one.     

Microstructure and Mechanical Properties of Al25 − xCr25 + 0.5xFe25Ni25 + 0.5x (x = 19, 17, 15 at%) Multi‐Component Alloys

A series of Al_{25 ? x}Cr_{25 + 0.5x}Fe₂₅Ni_{25 + 0.5x} (x = 19, 17, 15 at%) multi‐component alloys are prepared by arc‐melting and rapid solidification of copper molds. The technique of thermal‐mechanical processing is further applied to the master alloys to improve their mechanical properties. These alloys consist of face‐centered cubic (FCC) and body‐centered cubic (BCC) structure. The volume fraction of the BCC phase increases as Al content increase and Cr and Ni contents decrease, accompanied with a microstructural evolution from dendritic structure to lamella‐like structure. Due to the increase of volume fraction of BCC phase, the master alloys exhibit an increased strength and a declined ductility as Al content increases. The rapid solidified alloys have more BCC phase compared with the master alloys, which enhances the strength and decreases the ductility. After homogenization, hot‐rolling, and annealing at 1000 °C, the Al₈Cr_33.5Fe₂₅Ni_33.5 alloy displays excellent combination of strength (yield strength is ～635 MPa and fracture strength is ～1155 MPa) and ductility (tension strain is ～11%).

     

高熵合金强韧化方法及力学性能的研究进展

自高熵合金被首次报道以来,其优异的力学性能引起了国内外学者的广泛关注.高熵合金的高强度、高硬度、高耐磨性、耐腐蚀性以及其在极端温度下的服役能力,都表明高熵合金在未来工业应用中具有巨大潜力.随着对高熵合金的深入研究,从元素比例的改变到元素种类的改变再到新组元的添加,每一次高熵合金力学性能的优化与发展均伴随着结构的改变.尽管如此,高熵合金的力学性能依旧有很大的提升空间.因此,如何合理设计高熵合金的微观结构、提升其力学性能是当前研究的热点问题.在高熵合金中,已存在的强韧化方法有细晶强化、固溶强韧化、共晶组织强韧化、孪生诱导塑性(Twinning induced plasticity,TWIP)效应强韧化、相变诱导塑性(Transformation induced plasticity,TRIP)效应强韧化和第二相强韧化等.其中,细晶强化与第二相强化在绝大多数高熵合金中都存在且很容易通过热机械处理来实现.因此,如何在强化机理、组织特征、力学性能三者之间建立联系,是当前亟待解决的问题.本文归纳了高熵合金强韧化方法的研究进展,从高熵合金的优秀力学性能入手,分别介绍了固溶强化、短程有序(Short-range ordering,SRO)强化、γ'相强化、晶粒异构强韧化等结构设计理念,并且讨论了各种结构对高熵合金变形机制和力学性能的影响,分析了当前高熵合金的发展前景,以期为后续关于组织特征与力学性能建立有效联系提供参考.     

Additive Manufacturing of Advanced Multi‐Component Alloys: Bulk Metallic Glasses and High Entropy Alloys

Bulk metallic glasses (BMGs) and high entropy alloys (HEAs) are both important multi‐component alloys with novel microstructures and unique properties, which make them promising for applications in many industries. However, certain hindrances have been identified in the fabrication of BMGs and HEAs by conventional techniques due to the intrinsic requirements of BMGs and HEAs. With the advent of metal additive manufacturing, new opportunities have been perceived to fabricate geometrically complex BMGs and HEAs with tailorable microstructure theoretically at any site within the specimen, which are not achievable using conventional fabrication techniques. After providing some background and introducing the conventional fabrication techniques for BMGs and HEAs, this review will focus on the current status, development, and challenges in metal additive manufacturing of BMGs and HEAs including different additive manufacturing techniques being used, microstructure design and evolution, as well as properties of the fabricated BMGs and HEAs. A future outlook of metal additive manufacturing of BMGs and HEAs will also be provided at the end.

     

Micro‐Macroporous Composite Materials – Preparation Techniques and Selected Applications: A Review

Pores, on several orders of magnitude in size, control the properties of a solid material to a large extent. This is just as true for materials containing pores in the sub‐nanometer range like zeolites as for cellular foam structures with pores of several millimeters in size. All these porous materials have their distinct potential application ranging from heterogeneous catalysis to metal melt filtration. In many cases, the (hierarchical) combination of pores with different size regimes can improve the performance of the respective porous material or can lead to entirely new properties and applications. This review addresses the preparation and properties of microporous‐macroporous composite materials based on cellular foam supports (ceramic, metal, polymer) with a coating of a microporous compound (zeolite, zeotype framework, metal‐organic framework). The manufacturing of these materials can either be performed by dispersion‐based techniques, where the microporous coating is applied from a dispersion onto the cellular support (ex situ), or in situ by crystallization of the microporous compound directly onto the struts of the foam structure. In both cases, the general procedure can be modified by a pretreatment of the cellular support in order to improve the coating layer adherence, the overall amount of deposited material, or to control of the crystal morphology of the microporous compound.

     

Influence of Small Cr Addition on Thermal Stability and Magnetic Properties of Fe-Co-Zr-Nb-B Glassy Alloys

Fe62Cos-xCrxZr6Nb4B20 （x=0-4 at. pct） metallic glasses show high thermal stability with a maximum supercooled liquid region of about 84.8 K. The addition of 2 at. pct Cr causes the extension of the supercooled liquid region remarkably, leading to the enhancement of thermal stability and glass-forming ability. The crystallization of the Fe-based glassy alloys takes place through a single exothermic reaction, accompanying the precipitation of more than three kinds of crystallized phases such as α-Fe, Fe2Zr and ZrB2. The long-range atomic rearrangements required for the precipitation of the multiple crystalline phases seem to play an important role in the appearance of the large supercooled liquid region through the retardation of the crystallization reactions. The Fe-based alloys exhibit soft ferromagnetic properties. The saturation magnetization decreases with increasing Cr content while the saturated magnetostriction increases as a function of Cr content. There is no distinct change in the saturation magnetization and coercive force with annealing temperature below the crystallization temperature. The devitrification gives rise to a considerable enhancement in both as and He.