Irradiation Resistance of Multicomponent Alloys

High-entropy alloys (HEAs) are characterized not only by high values of entropy but also by high atomic-level stresses originating from mixing of elements with different atomic sizes. Particle irradiation on solids produces atomic displacements and thermal spikes. The high atomic-level stresses in HEAs facilitate amorphization upon particle irradiation, followed by local melting and re-crystallization due to thermal spikes. We speculate that this process will leave much less defects in HEAs than in conventional alloys. For this reason, they may be excellent candidates as new nuclear materials. We discuss initial results of computer simulation on model binary alloys and an electron microscopy study on Zr-Hf-Nb alloys, which demonstrate extremely high irradiation resistance of these alloys against electron damage to support this speculation.     

粉末冶金在高熵材料中的应用

高熵材料是近年来出现的一种新型材料,具有高强度、高硬度、良好耐腐蚀和优异的高温组织稳定性等性能,在航空航天、高温以及先进核能等领域展现了广阔的应用前景,引起国际材料领域的广泛关注,相关研究也取得了很大进展。粉末冶金作为一种高性能金属基和陶瓷复合材料的先进制备技术,可以获得纳米晶和过饱和固溶体等亚稳材料,同时也可用于传统熔炼法较难制备的具有特殊结构和性能的材料,近些年来,粉末冶金技术在高熵材料制备中得到广泛应用。本文从高熵材料的应用理论出发,针对目前高熵材料粉体制备方法、块体成型以及粉末冶金制备的典型高熵材料三个方面予以综述,着重阐述了高熵材料的力学性能和其变形行为特点,同时展望了高熵材料的未来发展趋势。      

Irradiation Behavior in High Entropy Alloys

As an increasing demand of advanced nuclear fission reactors and fusion facilities,the key requirements for the materials used in advanced nuclear systems should encompass superior high temperature property,good behavior in corrosive environment,and high irradiation resistance,etc.Recently,it was found that some selected high entropy alloys(HEAs) possess excellent mechanical properties at high temperature,high corrosion resistance,and no grain coarsening and self-healing ability under irradiation,especially,the exceptional structural stability and lower irradiation-induced volume swelling,compared with other conventional materials.Thus,HEAs have been considered as the potential nuclear materials used for future fission or fusion reactors,which are designed to operate at higher temperatures and higher radiation doses up to several hundreds of displacement per atom(dpa).An insight into the irradiation behavior of HEAs was given,including fundamental researches to investigate the irradiation-induced phase crystal structure change and volume swelling in HEAs.In summary,a brief overview of the irradiation behavior in HEAs was made and the irradiation-induced structural change in HEAs may be relatively insensitive because of their special structures.     

热喷涂制备高熵合金涂层的研究现状与展望

首先介绍了高熵合金的理论基础。然后从不同的热喷涂工艺出发,综述了等离子喷涂、超音速火焰喷涂、高速电弧喷涂、冷喷涂四种技术在制备高熵合金涂层上的研究发展现状,重点从原料选用、制备工艺优化、性能研究、后处理工艺等方面对以上四种热喷涂技术制备高熵合金涂层的研究进行系统地归纳与总结。最后提出现有制备高熵合金涂层的热喷涂技术较少、热喷涂材料受限、高熵合金设计盲目这三个问题,针对性地提出了在优化已有技术的基础上开发新技术;开发高熵陶瓷、高熵非晶合金、高熵复合材料等新型热喷涂材料;沿用材料基因组理念建立高熵合金数据库这三点热喷涂制备高熵合金涂层在未来的发展趋势。      

Plastic flow and fracture of metallic glass

The tensile flow and fracture behavior of three Pdo.₈Sio2-based alloys in the glassy, “microcrystalline,” and fully crystalline condition has been studied. The glassy alloys flow plastically to a total strain of approximately 0.5 pct e, and exhibit proportional limit stresses of approximatelyE x 10~² whereE is Young’s modulus. This plastic flow is accompanied by the formation of shear deformation bands on the specimen surfaces. Fully crystalline alloys are extremely brittle and fracture via intergranular cracking. Fracture surfaces of the amorphous and “microcrystalline” alloys are inclined at 45 deg to the tensile axis and exhibit two morphologically distinct zones. One zone is relatively featureless while the other contains a “river” pattern of local necking protrusions. Detailed comparison of opposing surfaces indicates that fracture is preceded by large local plastic shear which produces the smooth zone while the local necking pattern is produced during rupture. These observations form the basis for the hypothesis that plastic flow in the glassy material occurs via localized strain concentrations and that fracture is initiated by catastrophic, “adiabatic” shear. Formerly Postdoctoral Associate, Yeshiva University, New York, N. Y.     

Nano-/Ultrafine Eutectic in CoCrFeNi(Nb/Ta) High-Entropy Alloys

The development of single-phase high-entropy alloys (HEAs) emerges as a new paradigm shift in material research society during the last decade. A strong rise in the demand for structural and functional applications leads to the design and fabrication of super-strong eutectic HEAs through solidification processing. We report on the evolution of eutectic microstructure in CoCrFeNiNb_0.5 and CoCrFeNiTa_0.4 HEAs synthesized by arc melting. The evolved microstructure consists of nanolamellae of FCC γ-Ni and hexagonal β (Fe₂Nb or Co₂Ta type) Laves phases of 150 nm lamellae thickness. These alloys exhibit high yield strength of 2 GPa, ultimate compressive strength up to 2.2 GPa and 20% plastic strain. The strain rate jump test and transmission electron microscopic studies of deformed specimens have been performed to explore the microscopic mechanism of deformation in these high-strength advanced eutectic alloys.     

难熔高熵合金:制备方法与性能综述

从加工方法、微观结构以及各类性能三方面介绍了难熔高熵合金(Refractory high-entropy alloys,RHEAs),最后对难熔高熵合金的发展和未来进行了展望。以MoNbTaVW为代表的难熔高熵合金在高温下表现出优于传统镍基高温合金的压缩屈服强度,且屈服强度随温度的变化更加缓慢,高温力学性能优异;以MoNbTaVW、MoNbTaTiZr、HfNbTiZr等为代表的难熔高熵合金,与商用高温合金、难熔金属、难熔合金以及工具钢相比,展现出更优的耐磨性能。以W₃₈Ta₃₆Cr₁₅V₁₁合金为代表的难熔高熵合金在辐照后,除了析出小颗粒第二相外,不存在位错环缺陷结构,抗辐照性能优异。提出了难熔高熵合金未来发展的两大方向:建立高通量的实验和计算方法继续探索更多的难熔高熵合金组成和结构模型;探索多场耦合环境下难熔高熵合金的服役行为。      

FeCoCrNiMo high-entropy alloys prepared by powder metallurgy processing for diamond tool applications

High-entropy alloys (HEAs) show good mechanical properties like high strength, hardness and wear resistance, and this makes them attractive for application in diamond tools. However, there are severe obstacles to improving the mechanical properties of normal diamond tools with metal-matrix alloys. Here, we report the formation of FeCoCrNiMo HEAs by powder metallurgy processing, starting from a gas-atomised powder followed by mechanical milling and consolidation by spark plasma sintering. Our results show that FeCoCrNiMo HEAs with pure FCC phase can be obtained by this method. Specimens with higher hardness can be obtained at higher temperatures and low pressures, while specimens with higher bending strength are formed at lower temperatures and pressures. FeCoCrNiMo HEAs have remarkably higher hardness and better wear behaviour than metal-matrices commonly in used diamond tools, which indicates that a new type of diamond tool with superior properties can be realised from HEAs.

Special theme block on high entropy alloys, guest edited by Paula Alvaredo Olmos, Universidad Carlos III de Madrid, Spain, and Sheng Guo, Chalmers University, Gothenburg, Sweden.     

Tensile deformation of amorphous nickel-palladium-phosphorous alloys

Ni-Pd-P amorphous alloys show inhomogeneous plastic deformation, as do all other amorphous alloys. A few localized deformation bands appear macroscopically just beyond the elastic region of the stress strain curve. It is shown that two types of localized deformation bands can be produced during tensile deformation,i.e., one has sharp steps produced by plastic flow associated with a shear, and the other has interconnecting voids similar to a crazing crack in polymers.     

含Cu高熵合金的组织结构和力学性能分析

高熵合金（HEAs）是一种由5种或5种以上元素以接近等原子比的方式混合而成的一种新型合金。HEAs的概念为开发具有独特性能的先进材料提供了新的途径,这是传统的基于单一主导元素的微合金化方法无法实现的。由于Cu元素与HEAs中其他元素的混合焓均为正值,因而更容易偏聚形成富Cu的面心立方（fcc）结构。本文主要总结了合金成分、制备方法对含Cu HEAs组织结构的影响规律以及含Cu HEAs的热稳定性。例如Al的添加会使CoCrCuFeNi合金从fcc单相转变为fcc+bcc的双相结构,而Ni含量的增加则会将AlCoCrCuNi的多相组织转变为单相fcc结构。与传统铸造工艺相比,选区激光熔化和喷溅急冷等具有极高的冷却速度,限制了元素的扩散,因而制备而成的AlCoCuFeNi和AlCoCrCuFeNi合金均是bcc结构。组织结构的改变会进一步影响含Cu HEAs力学性能,因而本文也探讨了合金成分、制备工艺和服役温度与力学性能的关系。例如,V的添加可以提高合金的强度,以先进制备方法如选区激光熔化或激光粉末熔融得到的合金具有优于铸造合金的力学性能。     

Research on Bulk-metallic Glasses and High-entropy Alloys in Peter K. Liaw’s Group and with His Colleagues

Bulk-metallic glasses (BMGs) and high-entropy alloys (HEAs) have attracted extensive attention in the field of metallic materials research for several decades due to their extraordinary properties. Many scientists and researchers have significantly contributed to developing new classes of metallic alloys, such as BMGs and HEAs, for various applications. Liaw’s group and his colleagues have focused on the fundamental understanding of unique features, structures, and properties in BMGs and HEAs as well as the development of new types of metallic materials. In this article, we summarized the research work of Liaw’s group and his colleagues by reviewing relevant papers. The goal is to provide an understanding of the current research progression in BMGs and HEAs while further encouraging young and junior researchers to be involved in the field of structural materials research pertaining to these classes of exotic alloy systems.

     

热轧7075/AZ31B复合板的显微组织及结合性能

为了研究热轧铝/镁复合板结合强度的变化规律,本文综合考虑压下率、轧制温度和轧制速度等多种轧制参数,单道次热轧制备了7075 Al/AZ31B Mg复合板。结果表明:在复合板轧制过程中由于热和强变形作用组织发生了动态再结晶,且增大轧制速度有助于镁基体产生完全动态再结晶。在相同轧制温度下,铝镁复合板结合强度均随压下率增加先升高后降低;强度升高是由于界面元素扩散宽度的增大和镁合金近界面晶粒组织的细化所致,强度降低是由于大变形导致镁基体近界面处产生裂缝,以及塑性功产生热量过多使得镁基体温度升高导致的镁侧晶粒长大所致。对复合板进行拉剪实验,铝镁结合界面剪切强度较低时,断裂发生在复合界面处且成脆性断裂特征,强度较高时断口形貌呈韧性断裂特征,断裂发生在镁基体侧。      

Tensile deformation of amorphous nickel-palladium-phosphorous alloys

Ni-Pd-P amorphous alloys show inhomogeneous plastic deformation, as do all other amorphous alloys. A few localized deformation bands appear macroscopically just beyond the elastic region of the stress strain curve. It is shown that two types of localized deformation bands can be produced during tensile deformation,i.e., one has sharp steps produced by plastic flow associated with a shear, and the other has interconnecting voids similar to a crazing crack in polymers.     

含Cu镁锂合金组织与性能调控研究进展

镁锂合金具有超低密度、极高的比强度与比刚度、优异的电磁屏蔽性能及阻尼性能,目前广泛应用于追求轻量化的航空航天、新能源汽车、电子产品、生物医疗等领域。由于合金元素镁和锂均为活泼金属,在服役过程中镁锂合金会存在多种形式的腐蚀过程,同时二元镁锂合金强度较低,以上两点严重制约了其广泛应用。耐蚀涂层可以有效提高镁锂合金的腐蚀抗力,含铜镀层被证实能够提升镁锂合金耐蚀性。改善镁锂合金强度的工艺主要有合金化、热处理、加工变形等,其中合金化是最基本的强化手段。Cu合金化可以对镁锂合金中的组织与性能进行调控,改善镁锂合金的强度。本文对含Cu镁锂合金的研究进展及其应用情况进行综述,总结了目前含Cu镁锂合金耐蚀与力学性能的相关研究成果,重点梳理了铜元素在镁锂合金中的作用,为含Cu镁锂合金的实际应用提供一定的理论指导。     

Deformation and fracture of miniature tensile bars with resistance-spot-weld microstructures

Plastic deformation of miniature tensile bars generated from dual-phase steel weld microstructures (i.e., fusion zone, heat-affected zone, and base material) was investigated up to final rupture failure. Uniaxial tensile true stress-strain curves beyond diffuse necking were obtained with a novel strain-mapping technique based on digital image correlation (DIC). Key microstructural features (including defects) in each of these three metallurgical zones were examined to explore the material influence on the plastic deformation and failure behavior. For weld fusion zones with minimal defects, diffuse necking was found to begin at 6 pct strain and continue up to 55 to 80 pct strain. The flow stresses of the weld fusion zones were at least twice those of the base material, and fracture strains exceeded 100 pct for both materials. The heat-affected zones exhibited a range of complex deformation behaviors, as expected from their microstructural variety. Only those fusion zones with substantial defects (e.g., shrinkage voids, cracks, and contaminants) failed prematurely by edge cracking, as signaled by their highly irregular strain maps.     

铜合金的腐蚀与防护研究进展

铜合金具有良好的导电性和导热性,是应用最广泛的工业材料之一。铜合金服役过程中常与酸、碱、盐等腐蚀介质接触,易引起铜合金的腐蚀,最终导致失效,对生产制造带来危害。提高铜合金的耐腐蚀性有利于进一步扩展其应用领域。本文主要归纳了Cr, Pb, Ti, Al,Mn, Ni以及稀土元素的添加对合金耐蚀性能的影响,通过合金元素的添加可以改变铜合金表面腐蚀产物膜的组成和形貌,减小相与相之间腐蚀电位差,以及减少有害杂质的存在,以此来改善铜合金的耐蚀性能。塑性变形和热处理是改善铜合金力学性能的常用手段,经塑性变形和热处理过后的铜合金,其微观组织形貌和分布发生了变化,因此对合金耐蚀性能也有一定的影响。本文主要从合金化、塑性变形及热处理3个方面对铜合金耐蚀性能影响进行综述,最后对铜合金的腐蚀防护研究进行总结和展望。     

Microstructure and Mechanical Properties of the Ductile Al–Ti–Mo–Nb–V Refractory High Entropy Alloys

Metallurgical and Materials Transactions A - A number of non-equimolar refractory high entropy alloys (RF HEAs) from the Al–Ti–Mo–Nb–V system are synthesized, with the...     

High-entropy alloys fabricated via powder metallurgy. A critical review

High-entropy alloys (HEAs) have attracted a great deal of interest over the last 14 years. One reason for this level of interest is related to these alloys breaking the alloying principles that have been applied for many centuries. Thus, HEAs usually possess a single phase (contrary to expectations according to the composition of the alloy) and exhibit a high level of performance in different properties related to many developing areas in industry. Despite this significant interest, most HEAs have been developed via ingot metallurgy. More recently, powder metallurgy (PM) has appeared as an interesting alternative for further developing this family of alloys to possibly widen the field of nanostructures in HEAs and improve some capabilities of these alloys. In this paper, PM methods applied to HEAs are reviewed, and some possible ways to develop the use of powders as raw materials are introduced.     

激光熔覆高熵合金涂层组织结构及强化机理研究进展

激光熔覆作为一种绿色、高效的表面处理技术,能够快速制备组织致密、晶粒细小,与基体呈高强度冶金 结合的涂层,是近年来高熵合金领域的研究热点之一。概述了现有高熵合金涂层材料体系和制备方法,重点讨论 了激光熔覆CoCrFeNi-M 典型过渡族高熵合金涂层的组织结构,及其耐磨、耐蚀、抗高温氧化等性能,并归纳了 涂层的强化机制和方法。CoCrFeNi-M 系合金涂层主要呈现FCC 固溶体结构,综合力学性能普遍较好,通过合金 体系调控,在细晶强化、固溶强化、第二相强化等作用下,能够获得硬度、耐磨性、耐蚀性等性能的进一步提升。 同时,概述了激光熔覆难熔高熵合金涂层的组织结构,耐磨、耐蚀、抗高温氧化性能及性能强化机制,该体系合 金涂层主要呈现BCC 固溶体结构,硬度较高但室温韧性普遍不足,具有较好的高温强度,在高温领域具有较好 的应用前景,但抗高温氧化性能普遍不足,仍需通过合金体系优化进一步提升。此外,总结了基于激光熔覆技术 开展的高熵合金涂层制备及研究中存在的问题和不足,并展望了未来的发展方向。     

Application of Machine Learning Algorithms With and Without Principal Component Analysis for the Design of New Multiphase High Entropy Alloys

Metallurgical and Materials Transactions A - The design of high entropy alloys (HEAs) can be accelerated using machine learning (ML) algorithms. In the current study, the design parameter’s...