间隙原子对高熵合金组织及性能影响的研究现状

高熵合金作为一种新型的合金体系,虽然其组成元素复杂,但能形成简单的固溶体,具有许多异于传统合金的结构和性能特征,其研究近年来成为热点。间隙原子可以溶入基体晶格间隙产生固溶强化,与合金元素结合形成细小弥散强化相,以及降低层错能,改变位错运动方式等,从而改善高熵合金性能。文章在论述高熵合金组织结构特性的基础上,分析了间隙原子C、N、O、B对高熵合金相形成规律、强化机理、塑性变形机制的影响,总结了间隙原子含量及其产生的固溶强化、晶粒细化、第二相强化作用对高熵合金组织性能等方面影响的研究进展,最后提出了含间隙原子的高强高韧高熵合金组织结构设计研究的新方向。      

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.

     

铸态共晶高熵合金的研究进展

铸态共晶高熵合金在室温下的力学性能受到其化学成分、相组成和微观组织形貌的影响,是选用恰当的共晶高熵合金以适应于复杂服役环境的重要判据.文中通过调研近年来共晶高熵合金的相关文献,概述了共晶高熵合金的研究现状,按化学元素和共晶组织的相组成特点对共晶高熵合金进行了分类,即主要由FCC相+B2/BCC相组成的AlCoCrFeN...     

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。      

高熵合金的研究现状和应用前景

综述了高熵合金的制备方法、特性及其应用前景。高熵合金是近年发展起来的新型合金,通常包含5种以上的主要元素,各主元的原子分数在5%~35%之间,其组织和性能在许多方面有别于传统合金。随着对高熵合金研究的深入,其应用会越来越广,对各行各业的影响也会越来越大。     

Design of Novel Precipitate-Strengthened Al-Co-Cr-Fe-Nb-Ni High-Entropy Superalloys

A series of non-equiatomic Al-Co-Cr-Fe-Nb-Ni high-entropy alloys, with varying levels of Co, Nb and Fe, were investigated in an effort to obtain microstructures similar to conventional Ni-based superalloys. Elevated levels of Co were observed to significantly decrease the solvus temperature of the γ′ precipitates. Both Nb and Co in excessive concentrations promoted the formation of Laves and NiAl phases that formed either during solidification and remained undissolved during homogenization or upon high-temperature aging. Lowering the content of Nb, Co, or Fe prevented the formation of the eutectic type Laves. In addition, lowering the Co content resulted in a higher number density and volume fraction of the γ′ precipitates, while increasing the Fe content led to the destabilization of the γ′ precipitates. Various aging treatments were performed which led to different size distributions of the strengthening phase. Results from the microstructural characterization and hardness property assessments of these high-entropy alloys were compared to a commercial, high-strength Ni-based superalloy RR1000. Potentially, precipitation-strengthened high-entropy alloys could find applications replacing Ni-based superalloys as structural materials in power generation applications.

     

Microstructures and properties of CoCrCuFeNiMox high-entropy alloys fabricated by mechanical alloying and spark plasma sintering

CoCrCuFeNiMox (x values in molar ratio, x?=?0, 0.2, 0.4 and 0.8) high-entropy alloys were prepared by mechanical alloying and spark plasma sintering method. The effects of Mo addition on microstructure and mechanical properties were investigated. The X-ray diffraction (XRD) result showed that the addition of Mo into CoCrCuFeNi high-entropy alloy (HEA) changed the original phase constitution from FCC to FCC?+?σ?+?μ and the peak intensity of (1 1 1) shifted to the left and decreased steadily. The field emission scanning electron microscope confirmed that the Cu-rich second FCC phase disappeared and the σ phase with a tetragonal structure expanded as the Mo content was increased. Additionally, a high density of dimple-like features were seen in CoCrCuFeNi HEA while typical quasi-cleavage facets could be observed from the fracture surfaces of the HEAs with the addition of Mo. The Mo0.8 alloy showed a good wear resistant and appropriate strength with fracture strain 22.70%, fraction coefficient 0.65, hardness 530?HV and compressive strength 1448?MPa.

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.     

Processing and characterisation of nano crystalline AlCoCrCuFeTix high-entropy alloy

In this work multi-component equiatomic and non-equiatomic AlCoCrCuFeTi_x hexanary high-entropy alloys (HEA) was synthesised through mechanical alloying. The prepared powder was sintered via spark plasma sintering. Influence of alloying element variation in the multi-component system was studied in terms of phase formation and crystal structure by using Thermo-Calc and X-ray diffraction characterization technique (XRD). Particle morphology and chemical analysis studies were carried out through scanning electron microscopy along with Electron Dispersive X-ray Spectroscopy. The crystal structure and nano crystallinity of the hexanary system were recognised using transmission electron microscope (TEM and Selected Area Electron Diffraction [SAED]) while the formation of a solid solution was also studied and discussed. From the XRD and TEM characterisation of 20?h in, milled powders and sintered samples, it was confirmed that the developed HEA system forms a single solid solution BCC phase. The sintered alloy exhibits 97% relative density and an average hardness of 590?VHN.

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.     

粉末冶金发展现状及趋势

文章评述了粉末冶金技术在机械零件、摩擦材料、电工材料、硬质合金、难熔金属材料、金刚石—金属工具、航空结构材料、非晶态合金、精细陶瓷、功能材料等领域国内外的研究开发现状及新工艺等的发展趋势。     

选区激光熔化CoCrFeNi-X高熵合金的研究进展

CoCrFeNi高熵合金因其单一稳定的面心立方固溶体结构,具有优异的塑性变形能力和较高的屈服强度,已成为众多追求高韧性制件研究的热门体系之一。同时选区激光熔化技术因其成形尺寸灵活和超快加热冷却速率,具备传统制备方式不可比拟的优势。通过梳理近些年选区激光熔化技术成功制备出的CoCrFeNiX高熵合金体系,首先针对8种不同合金体系的相结构和组织形貌,分析了组织结构对力学性能的影响;其次针对3种采用不同工艺参数制备的CoCrFeNi-X高熵合金成形件,分析制备工艺对成形密度及力学性能的影响;最后就合金成分设计对CoCrFeNi-Alx、CoCrFeNi-Mn两种主流合金体系做了详细研究现状分析。期望对采用选区激光熔化技术制备CoCrFeNi-X体系高熵合金的实验研究和工业应用提供一定的理论指导。     

Evaluation of Thermal and Mechanical Behavior of CuNiCoZnAl High-Entropy Alloy Fabricated Using Mechanical Alloying and Spark Plasma Sintering

Thermal behavior investigation of CuNiCoZnAl high-entropy alloy powder produced by mechanical alloying indicated that a FCC single-phase solid solution transformed into two new phases at 500 °C. Despite this phase transformation, no indication of intermetallic compounds or amorphous phases was detected. Heat treatment of the high-entropy alloy was then carried out for 2 hours, and the nanocrystalline structure of heat-treated milled powder was retained up to 1000 °C. Besides, grain growth of CuNiCoZnAl high-entropy alloy powder at high homologous temperatures (> 0.6 T_m) was studied, and sluggish grain growth of the powder was observed clearly. Consolidation of the alloy powder was performed by spark plasma sintering at 800 °C, and a sample with porosity of 6.87 pct and density of 7.32 g cm⁻³ was achieved. Elastic moduli, Vickers microhardness, and fracture toughness of the bulk sample were measured as 186 ± 17 GPa, 599 ± 31 HV, and 4.45 MPa m^0.5, respectively. The evaluation of wear behavior indicated that the dominant wear mechanism was adhesive wear. Moreover, tribochemical wear (oxidation) was found to be the minor wear mechanism. The present study revealed that CuNiCoZnAl high-entropy alloy has the potential to be used in many applications that high hardness and low elastic moduli are favorable.

     

A Brief Review of High Entropy Alloys and Serration Behavior and Flow Units

Multicomponent alloys with high entropy of mixing,e.g.,high entropy alloys (HEAs)and/or multiprin-cipal-element alloys (MEAs),are attracting increasing attentions,because the materials with novel properties are being developed,based on the design strategy of the equiatomic ratio,multicomponent,and high entropy of mixing in their liquid or random solution state.Recently,HEAs with the ultrahigh strength and fracture toughness,excel-lent magnetic properties,high fatigue,wear and corrosion resistance,great phase stability/high resistance to heat-softening behavior,sluggish diffusion effects,and potential superconductivity,etc.,were developed.The HEAs can even have very high irradiation resistance and may have some self-healing effects,and can potentially be used as the first wall and nuclear fuel cladding materials.Serration behaviors and flow units are powerful methods to understand the plastic deformation or fracture of materials.The methods have been successfully used to study the plasticity of amorphous alloys (also bulk metallic glasses,BMGs).The flow units are proposed as:free volumes,shear transi-tion zones (STZs),tension-transition zones (TTZs),liquid-like regions,soft regions or soft spots,etc.The flow units in the crystalline alloys are usually dislocations,which may interact with the solute atoms,interstitial types,or sub-stitution types.Moreover,the flow units often change with the testing temperatures and loading strain rates,e.g., at the low temperature and high strain rate,plastic deformation will be carried out by the flow unit of twinning,and at high temperatures,the grain boundary will be the weak area,and play as the flow unit.The serration shapes are related to the types of flow units,and the serration behavior can be analyzed using the power law and modified power law.     

The Influence of 3d and 4d Transition Metals on the Glass Forming Ability of Ternary FeCo-Based Alloys

Thermodynamic modeling was used to determine enthalpies of formation and other thermodynamic parameters describing glass forming ability of Fe-Co-TM (TM = V, Nb, Cr, Mo) alloys. FeCo-based alloys are considered as candidates for applications as high magnetic flux density materials due to their high magnetic saturation and low magnetic anisotropy. Nevertheless, mechanical properties, especially the lack of ductility, are their main weakness. Therefore, further optimization by vitrification, further heat treatment and alloying should be considered. As the most crucial step is the synthesis of amorphous precursors, discussion is concentrated on the effect of transition metal substitution on the glass forming ability. The highest glass forming ability was reported for Fe-Co-Nb alloys. It can be also noted that the driving force for vitrification can be improved by substitution of Fe by other transition elements, as glass forming ability parameter ∆P_HS reaches the lowest values for Fe-less compositions.

     

On Prediction of Amorphous Phase Forming Compositions in the Iron-Rich Fe-Zr-B Ternary System and Their Synthesis

A thermodynamic model parameter P _H-S , which is a product of enthalpy of chemical mixing and mismatch entropy normalized by Boltzmann’s constant, was used as a guiding tool to predict amorphous phase forming compositions in Fe-rich alloys of the Fe-Zr-B system. Attempts were made to evaluate the effect of Zr addition on the P _H-S parameter and phase formation by mechanical alloying (MA) and rapid solidification processing (RSP). A systematic evaluation of the P _H-S parameter of various binary compounds in the Fe-Zr-B system and ternary alloys indicated ~–7 kJ/mol as a lower bound for the formation of amorphous phase. Model predictions were verified with phase formation in two random compositions in the Fe-rich end of the Fe-Zr-B system synthesized by MA and RSP.     

THE HIGH-TEMPERATURE PROPERTIES OF CERAMICS AND CERMETS

Abstract

It has been recognized for some time that, with progressive increase in the working temperature of gas turbines, metallic alloys may no longer be adequate for rotor or stator blading. The use of more refractory but more brittle materials, i.e. ceramics and ceramic-metal mixtures (cermets) has been suggested. The paper is concerned with the evaluation of the major properties involved, viz. creep strength, fatigue strength, resistance to thermal fatigue (i.e. to repeated thermal shocks), oxidation-resistance, and impact-resistance. The materials evaluated include oxides, oxide–metal cermets, carbides, carbide-metal cermets, molybdenum disilicide, and silicon nitride. The equipment for determining the effects of alternating and steady mechanical stresses up to 1200° C. is described. The relative merits of the test materials are discussed. It is concluded that the resistance to thermal fatigue and to impact of the ceramics and cermets is inferior to that of metallic alloys in current use.     

FeCrVTa0.4W0.4高熵合金氮化物薄膜的微观结构与性能

实验利用单靶射频磁控溅射技术,在单晶硅基底上,制备了两个系列FeCrVTa_0.4W_0.4高熵合金氮化物薄膜,即FeCrVTa_0.4W_0.4氮化物成分梯度多层薄膜和(FeCrVTa_0.4W_0.4)N_x单层薄膜,其中,多层薄膜用于太阳光谱选择性吸收薄膜。通过扫描电子显微镜(SEM)、X射线衍射仪(XRD)、纳米力学探针、原子力显微镜(AFM)、紫外?可见分光光度计、接触角测量仪和四探针测试台对FeCrVTa_0.4W_0.4高熵合金氮化物薄膜进行微观结构分析以及性能表征。结果表明:在不通入氮气时,薄膜为非晶结构,当氮气含量升高后,转变为面心立方固溶体结构;当表层氮气流量为15 mL·min?1时,FeCrVTa_0.4W_0.4氮化物多层薄膜及单层薄膜均具有最佳的力学性能,其中,多层薄膜的硬度为22.05 GPa,模量为287.4 GPa,单层薄膜的硬度为22.8 GPa,模量为280.7 GPa,随着表层氮气含量的继续增加,力学性能下降;FeCrVTa_0.4W_0.4氮化物成分梯度多层薄膜在300～800 nm波长范围内均具有太阳光谱选择吸收性,当氮化物薄膜层数较少时具有较好的疏水性;(FeCrVTa_0.4W_0.4)N_x单层薄膜随着氮气含量的增加,薄膜方块电阻增加。      

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。      

Ferroelectric ceramics for information storage and display

The electrooptic properties of hot-pressed lead zirconate titanate ceramics and their applications are reviewed. Coarse-grained, bismuth-doped ceramics with average grain size greater than 2 ?m have light scattering properties that can be varied by switching the orientation of the ferroelectric polarization. Fine-grained bismuth-or lanthanum-doped ceramics have an effective birefringence that can be varied either by applying an external electric field (conventional electrooptic effect) or by partially switching the remanent polarization (electrooptic memory effect). Ba, Sn, or La modifications of the lead zirconate titanate system produce materials with improved switching characteristics and electrooptic effects similar to those of fine-grained bismuth-or lanthanum-doped ceramics. Lanthanum modified lead zirconate titanate (PLZT) is significantly more transparent than other electrooptic ceramics. The PLZT system includes materials with electrooptic memory and either linear or quadratic electrooptic effects. The electrooptic properties of modified lead zirconate titanate ceramics, especially PLZT, combined with localized switching and modulation capabilities are particularly suitable for information storage and display devices.

     

Powder metallurgy and high-entropy alloys: update on new opportunities

ABSTRACT

This article addresses the development of high-entropy alloys (HEAs) fabricated via Powder Metallurgy (PM) techniques. There are potential opportunities for PM techniques to produce ‘different’ HEAs and offer alternative routes to obtain special compositions. The potential for PM is vast, and the obtained properties are highly competitive with those from HEAs produced by ingot casting. Considerable work must still be done to provide the market with reasons to use PM instead of other processing routes. Since article [Torralba JM, Alvaredo P, García-Junceda A. High-entropy alloys fabricated via powder metallurgy. A critical review. Powder Metall. 2019;62(2), doi:10.1080/00325899.2019.1584454] was published in 2019, more than 100 research works have been issued on this topic. The objective of this paper is to provide an update on some of the new opportunities that have been proposed in the last months.     

高饱和磁化强度铁基非晶纳米晶软磁合金发展概况

概括了铁基非晶软磁合金和纳米晶合金的发展历史和现状,分别详述了高饱和磁化强度(B_s)铁基块体和薄带非晶以及纳米晶合金近年来的研究成果.主要内容包括:高饱和磁化强度块体铁基非晶软磁合金成分和性能,高饱和磁化强度铁基非晶薄带软磁合金的成分和性能,高饱和磁化强度铁基纳米晶合金的组织、结构和性能,各类元素对合金磁性能的影响.为进一步研究高饱和磁化强度的铁基软磁材料提供了有价值的参考.