Alloying has long been used to confer desirable properties to materials. Typically, it involves the addition of relatively small amounts of secondary elements to a primary element. For the past decade and a half, however, a new alloying strategy that involves the combination of multiple principal elements in high concentrations to create new materials called high-entropy alloys has been in vogue. The multi-dimensional compositional space that can be tackled with this approach is practically limitless, and only tiny regions have been investigated so far. Nevertheless, a few high-entropy alloys have already been shown to possess exceptional properties, exceeding those of conventional alloys, and other outstanding high-entropy alloys are likely to be discovered in the future. Here, we review recent progress in understanding the salient features of high-entropy alloys. Model alloys whose behaviour has been carefully investigated are highlighted and their fundamental properties and underlying elementary mechanisms discussed. We also address the vast compositional space that remains to be explored and outline fruitful ways to identify regions within this space where high-entropy alloys with potentially interesting properties may be lurking.

High-entropy alloys overcome the limitations posed by traditional alloys due to features such as high strength, toughness, high wear resistance, and corrosion resistance. These alloys are novel metallic materials with excellent application potential; however, typically an inverse relationship is observed between the strength and ductility of a metal, which includes high-entropy alloys. Therefore, the design and development of high entropy alloys with high strength and high ductility have become a limitation in current research. Recently, heterostructure design has achieved great success in strengthening and toughening traditional metallic materials. Heterostructured and high-entropy alloys has garnered much attention and research interest to realize the strength and toughness of high-entropy alloys with high strength and high ductility. This study reviews the existing design models for heterostructures from the heterostructure scale perspective. Furthermore, the effects of different heterostructures on the strengthening and toughening mechanism and mechanical properties were analyzed, and future microstructural designs with high strength and toughness were anticipated.

高熵合金突破了传统合金设计理念的桎梏,具有高强度、高硬度、高耐磨性及抗腐蚀性,是一种具有巨大发展前景的新型金属材料。然而,金属材料的强度与塑性之间存在倒置矛盾关系,高熵合金仍受困于这一难题。因此,设计开发兼具高强度与高塑性的高熵合金材料已成为目前研究热点与难点。近年来,异构设计理念在传统金属材料强韧化这一问题上得到发展,如何设计异构高熵合金以实现高熵合金强韧化,使合金兼具高强度与高塑性,引起了科研人员的重视。本文从异构显微组织尺度出发,综述了目前存在的异构显微结构设计方法,分析了不同异构组织对其强韧化机制及力学性能的影响,并对未来高强韧高熵合金显微结构设计进行了展望。

The microstructure of the as-cast AlCoCrFeNi high entropy alloy has been investigated by transmission electron microscopy and atom probe tomography. The alloy shows a very pronounced microstructure with clearly distinguishable dendrites and interdendrites. In both regions a separation into an Al-Ni rich matrix and Cr-Fe-rich precipitates can be observed. Moreover, fluctuations of single elements within the Cr-Fe rich phase have been singled out by three dimensional atom probe measurements. The results of investigations are discussed in terms of spinodal decomposition of the alloying elements inside the Cr-Fe-rich precipitates. Copyright © 2012 Elsevier B.V. All rights reserved.

Structural considerations for designing a high-temperature oxidation-resistant metallic material are proposed, based on the dependence of the material structure on a promotion of the development of a protective scale of chromia or alumina. The material should have numerous sites on its surface for nucleating the protective oxides at the onset of oxidation and abundant grain boundaries in deeper areas for simultaneously supplying sufficient flux of the protective-oxide-forming elements toward the surface for a rapid linkage of the oxide nuclei through their lateral growth. Based on these considerations, we fabricated, using an electrochemical deposition method, novel nanocomposites which have a nanocrystalline metal matrix containing Cr and/or Al nanoparticles dispersed at the nano length scale. The validity of the design considerations is verified by comparing the high-temperature oxidation of a typical Ni-Cr nanocomposite system with two types of conventional Ni-Cr materials having similar or higher Cr content but different structure: one is a composite having a nanocrystalline Ni matrix containing Cr microparticles dispersed at the microscale and the other are micron-grained Ni-Cr alloys with the Cr distribution at the atomic length scale.

通过机械合金化 (MA) 和放电等离子烧结 (SPS) 制备了Cr₂O₃颗粒强化的超细晶结构镍基高温合金 (ODS合金)。对比研究了不添加氧化物颗粒合金 (Base合金) 和ODS合金样品的微观结构和高温氧化行为。结果表明,在1200 ℃烧结过程中,Cr₂O₃完全转变为Al₂O₃。由于SPS快速烧结及弥散分布的原位Al₂O₃颗粒钉扎,抑制了晶粒长大,ODS合金具有十分细小的晶粒结构,其平均晶粒尺寸为0.98 μm；Base合金平均晶粒尺寸稍大,为1.54 μm。ODS合金在900 ℃下具有较好的抗氧化性能和较低的氧化速率,得益于其表面迅速生成了连续致密的内层α-Al₂O₃膜,能有效地阻止Ti和Cr向外扩散,表面生成少量保护性较差的TiO₂和NiCr₂O₄。而Base合金表面则生成了以Al₂O₃为内层,TiO₂和Cr₂O₃为中间层以及NiCr₂O₄为外层的多层结构氧化膜,并且其在初期的氧化速率较快,为1.66×10^-7 mg²·cm^-4·s^-1,是ODS合金的2倍多。