金属学报, 2025, 61(1): 1-11 DOI: 10.11900/0412.1961.2024.00250

综述

共晶高熵合金十年发展回顾(20142024):设计、制备与应用

王志军,1, 白晓昱1, 王健斌1, 姜慧2, 焦文娜3, 李天昕4, 卢一平,3,5

1 西北工业大学 凝固技术国家重点实验室 西安 710072

2 山东科技大学 机械电子工程学院 青岛 266590

3 大连理工大学 材料科学与工程学院 大连 116024

4 贵州大学 材料与冶金学院 贵阳 550025

5 大连理工大学 辽宁省高熵合金材料工程研究中心 大连 116024

Revisiting the Development of Eutectic High-Entropy Alloys over the Past Decade (2014-2024): Design, Manufacturing, and Applications

WANG Zhijun,1, BAI Xiaoyu1, WANG Jianbin1, JIANG Hui2, JIAO Wenna3, LI Tianxin4, LU Yiping,3,5

1 State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an 710072, China

2 School of Mechanical and Electronic Engineering, Shandong University of Science and Technology, Qingdao 266590, China

3 School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024, China

4 College of Materials and Metallurgy, Guizhou University, Guiyang 550025, China

5 Liaoning Engineering Research Center of High-Entropy Alloy Materials, Dalian University of Technology, Dalian 116024, China

通讯作者: 王志军,zhjwang@nwpu.edu.cn,主要从事高熵合金设计与强韧化的研究;卢一平,luyiping@dlut.edu.cn,主要从事高熵合金的成分设计理论以及制备技术的研究

责任编辑: 肖素红

收稿日期: 2024-07-23   修回日期: 2024-09-11  

Corresponding authors: WANG Zhijun, professor, Tel: 13484671484, E-mail:zhjwang@nwpu.edu.cn;LU Yiping, professor, Tel:(0411)84709400, E-mail:luyiping@dlut.edu.cn

Received: 2024-07-23   Revised: 2024-09-11  

作者简介 About authors

王志军,男,1984年生,教授

摘要

共晶合金是以凝固过程发生共晶反应命名的一类多相合金,具有悠久的历史,是应用最广的铸造合金。高熵合金是多主元的新型合金,自2004年提出以来取得了迅速发展。共晶高熵合金结合了共晶合金和高熵合金的优点,于2014年首次公开报道。经历十年发展,共晶高熵合金已经快速经历了成分设计、组织/性能调控、大规模制备与应用几个阶段。共晶高熵合金独特的微观组织特征和优异的综合性能使其在多个领域展现出广阔的应用前景,成为近年来备受关注的新型合金材料。本文对过去十年共晶高熵合金的成分设计、制备和应用进展进行了回顾,并对未来发展趋势进行了展望。

关键词: 共晶高熵合金; 成分设计; 组织调控; 材料制备; 应用

Abstract

Eutectic alloys are a class of multi-phase materials named for their formation through eutectic reactions during solidification. They have a long history as the most widely used casting alloys. High-entropy alloys (HEAs), on the other hand, are a novel class of multi-principal element alloys that have rapidly developed since their conceptualization in 2004. Combining the advantages of eutectic alloys and HEAs, eutectic high-entropy alloys (EHEAs) were first proposed in 2014. Over a decade, EHEAs have been systematically investigated by focusing on alloy design, microstructure/performance optimization, large-scale fabrication, and potential applications. Their unique microstructures and excellent comprehensive properties have made EHEAs promising materials across various domains, garnering significant attention in recent years. By revisiting the advances in composition design, manufacturing, and applications of EHEAs over the past decade, this review offered insights into future trends and developments in this rapidly evolving field.

Keywords: eutectic high-entropy alloy; composition design; microstructure control; material manufacturing; application

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本文引用格式

王志军, 白晓昱, 王健斌, 姜慧, 焦文娜, 李天昕, 卢一平. 共晶高熵合金十年发展回顾(20142024):设计、制备与应用[J]. 金属学报, 2025, 61(1): 1-11 DOI:10.11900/0412.1961.2024.00250

WANG Zhijun, BAI Xiaoyu, WANG Jianbin, JIANG Hui, JIAO Wenna, LI Tianxin, LU Yiping. Revisiting the Development of Eutectic High-Entropy Alloys over the Past Decade (2014-2024): Design, Manufacturing, and Applications[J]. Acta Metallurgica Sinica, 2025, 61(1): 1-11 DOI:10.11900/0412.1961.2024.00250

传统合金通常以其主要元素命名,例如钢、铝合金、钛合金、镁合金、铜合金等。有别于单一主元的传统合金,高熵合金则由多种主要元素组成,通常多于3种主元,亦被称为多主元合金[1,2]。高熵合金以高构型熵得名,早期以构型熵大于1.5R (R = 8.314 J/(K·mol),为气体常数)这一临界值为特征[3]。随着研究的逐步深入,高熵合金的熵效应与材料性能的对应关系逐渐弱化,逐步衍生出中熵合金、多主元合金、复杂成分合金等不同的名称。现有高熵合金的命名方式有2种:一种基于主要组成相晶体结构命名,例如fcc高熵合金、bcc高熵合金、hcp高熵合金等;另一种以主要元素集合命名,例如FeCoNiCrMn高熵合金[2,4]、NbWTaMo高熵合金[5,6]、TiZrHfNbTa高熵合金[7,8]等。2004年以来,高熵合金得到了持续、广泛的关注。近年来,每年在高熵合金领域发表的科学论文数量达到上千篇。高熵的概念也被借鉴到高熵陶瓷[9,10]、高熵聚合物[11]等其他材料领域。

共晶合金是以凝固过程命名的一类特殊多元、多相合金。共晶凝固过程中,液相同时凝固成2种或多种不同晶体结构的固相。凝固后共晶相的组织在微观尺度上呈片层、纤维状或者不规则形貌,以自生复合材料的形式存在。共晶合金的凝固过程和微观组织特点使其具有优异的铸造性能和力学性能,在工业界得以广泛应用[12]。结合高熵合金和共晶合金的特点,Lu等[13]在2014年提出了共晶高熵合金(eutectic high-entropy alloys,EHEAs)的概念,并开发出首个具有完全共晶成分的AlCoCrFeNi2.1高熵合金。此合金由fcc/B2两相共晶组成,具有优异的铸造性能和综合力学性能[14]。共晶高熵合金在凝固过程中发生了典型的共晶反应,通常形成与传统共晶合金类似的交替层片状共晶组织。与传统共晶合金不同的是,共晶高熵合金中共晶相的成分组成均具有多主元特征,因此兼具共晶合金和高熵合金的优点。

共晶高熵合金自提出以来,其独特的相组成和优异的性能引起国内外广泛关注。共晶高熵合金在成分设计、凝固组织调控、凝固机理和大体积高纯净铸锭制备技术等方面都取得了突破性进展[15~18]。共晶高熵合金的性能不仅取决于构成相的成分和晶体结构特性,也受微观组织形貌的影响。高性能的共晶高熵合金需要对成分和组织同时进行调控,以获得综合性能优异的金属材料。组织调控过程主要包含凝固及后续的热机械处理,涉及相变、界面、位错、再结晶和析出动力学等基础科学问题。随着共晶高熵合金基础研究的不断完善,其工程化应用需要进行大规模制备以及应用环境评估测试,例如抗氧化性能、抗腐蚀性能、持久性能、蠕变性能、疲劳性能等。

共晶高熵合金的研究和开发引领了先进金属材料的发展。短短十年,共晶合金从成分设计到组织/性能调控取得了一系列重大的突破。近年来已经出现了大规格共晶高熵合金制备的相关报道。本文将重点梳理十年来共晶高熵合金领域的关键突破,总结关键科学问题和挑战,展望未来发展方向,以期促进共晶高熵合金的进一步发展。

1 共晶高熵合金的成分设计

二元共晶合金有完备的热力学成分数据库,而高熵合金成分构成非常复杂,因此对其共晶成分的预测变得非常困难。共晶高熵合金成分设计经历了早期的经验设计、热力学半定量设计、后期的大数据分析设计等过程[19]

基于从简单到复杂的原理,共晶高熵合金的成分设计从现有二元共晶合金获得思路。早期对单相高熵合金固溶体的相选择开展了大量研究工作[20],通过在二元相图中寻找与单相固溶体组成元素均有共晶反应的元素设计共晶高熵合金。以CoCrFeNi等比例高熵合金为基体,首先发现Nb与CoCrFeNi间存在共晶反应[21]。进一步地,采用伪二元相图计算方法开发出具有完全共晶成分的CoCrFeNiNb0.65共晶高熵合金,如图1a[22]所示。后续的研究[23]表明,Nb、Ta、Hf、Zr等元素与Ni、Co、Fe、Cr等元素均存在共晶反应。如图1b1~b4[23]所示,通过这些二元共晶成分的等比例混合,可实现(CoCrFeNi)Mx (M  =  Nb、Ta、Hf、Zr)共晶高熵合金的设计。基于此,大量的共晶高熵合金成分被开发出来。随后,在这些共晶高熵合金成分基础上形成了一系列基于热力学参数的经验设计准则[24,25],如图1c[25]所示,例如混合焓(ΔHmix)、混合熵(ΔSmix)、原子半径差(δr)、价电子浓度(VEC)等。在这些热力学经验参数的指导下,Fe、Co、Ni、Cr 4种元素组成的单相固溶体能够以非等比例成分出现,其共晶成分需要结合相图计算和实验进行确定。

图1

图1   共晶高熵合金的成分设计方法[22,23,25,26]

Fig.1   Strategies to design eutectic high-entropy alloys (EHEAs)

(a) calculated pseudo-binary-phase diagram for FeCoNiCrNb x alloys[22] (b1-b4) microstructures of (CoCrFeNi)Mx EHEAs obtained by the simple mixing method[23] (c) empirical design criteria for EHEAs based on the relationship between valence electron concentration (VEC) and atomic size difference (δr)[25] (d) empirical design criteria for EHEAs based on the relationship between mixed enthalpy of solid solution (ΔHmixss) and VEC of solid solution (VECss) (IMC—intermetallic compound)[26]


在某些体系中,基于二元共晶反应设计共晶高熵合金的方法存在一定局限性。例如,在AlCoCrFeNi合金体系中,Al与Cr元素之间不存在二元共晶反应。如何在AlCoCrFeNi体系中快速找到共晶成分仍然缺少有效的方法。早期,依靠大量实验研究确定了AlCoCrFeNi体系中的一些共晶成分,例如最初报道的AlCoCrFeNi2.1[13]。尽管AlCoCrFeNi体系多元相图的截面中存在类似于二元合金体系的共晶相图,其共晶成分范围仍难以直接确定。对此,一些基于共晶两相混合法则的热力学经验方法被提出,例如ΔHmix和VEC判据等,如图1d[26]所示。

在积累了大量实验数据后,机器学习方法被引入到共晶高熵合金成分设计中来,其示意图如图2[27]所示。基于卷积神经网络的机器学习模型快速给出了AlCoCrFeNi体系中众多共晶高熵合金成分。分析发现,AlCoCrFeNi体系中共晶成分设计存在3个原则:一是该体系中Al元素是决定共晶成分的关键元素,其共晶含量分布在16%~18% (原子分数)的很窄区间内;二是Cr元素与Al元素有比较强的相关性,通过给定的Al元素成分可以确定Cr元素的成分范围;三是Fe、Co、Ni 3种元素之间有很高的固溶度,其对共晶成分的影响可以借助VEC描述。在Al和Cr含量固定的情况下,fcc相体积分数随Ni、Co、Fe平均VEC的增加而增加。借此,设计给定高熵合金体系的共晶成分可以遵循以下步骤:首先确定共晶成分的关键元素及其含量,其次确定关联元素及其成分范围,最终确定固溶元素的成分范围。

图2

图2   机器学习辅助的共晶高熵合金成分设计方法[27]

Fig.2   Schematic diagram of designing EHEAs with machine learning[27] (xi is the ith input parameter, y is the output parameter. The f1(x) and f2(x) are the internal layer functions in an artificial neural network model)


目前,共晶高熵合金的成分仍有很大的优化空间,通过添加微合金化元素可以显著优化其性能。研究[28~31]表明,Ti、Mo、W、Nb等元素可以在fcc/B2共晶高熵合金中起到显著的固溶强化作用,并可诱导Laves相、μ相等强化相的析出,从而进一步提升其力学性能。随着共晶高熵合金的不断发展,针对提升其高温性能的合金化方法也得到了一定的研究。Chen等[32]研究发现,Hf元素的添加能够促使晶界处富Hf相的析出,在高温变形过程中有效地阻碍晶界滑动。此外,Jia等[33]在Ni30Co30Cr10Fe10Al18W2合金中添加非金属元素B,发现B元素的偏聚能够润滑fcc/B2相界,促进相界面的应力传递。此外,沿晶界析出的M3B2硼化物能够钉扎高温下弱化的晶界,在800 ℃下屈服强度和断裂延伸率分别达到581 MPa 和71%。这些微合金化策略为开发高温共晶高熵合金提供了新思路。

2 共晶高熵合金的组织和性能调控

共晶高熵合金具有自生复合材料的特征,微观尺度上共晶相以规则片层、纤维状或其余不规则的形貌呈现。如图3a[34]所示,Lu等[34]在直接铸造的AlCoCr1.8FeNi和AlCoCr2FeNi共晶高熵合金中观察到了超细的纤维状bcc/B2双相组织,其双相尺寸仅为100~300 nm,为制备块体超细材料提供了一种高效率、低成本的途径。多数共晶高熵合金表现为层片或层片/不规则混合组织。层片组织广泛存在于fcc/Laves共晶高熵合金中,在fcc/B2高熵合金中也少量存在,其组织通常较细[35~37]。如图3b[38]所示,铸态CoCrFeNiNb0.45共晶高熵合金的层片间距仅为200 nm。层片/不规则混合组织常见于AlCoCrFeNi系共晶高熵合金,通常由晶粒中部数层平直的层片组织与周围相对较粗的等轴双相组织构成[39~41],如图3c[39]所示。

图3

图3   典型共晶高熵合金凝固组织[34,38,39]

Fig.3   Typical solidification microstructures of EHEAs

(a) ultrafine eutectic microstructure (A and B show the dendritic and inter-dendritic regions, respectively)[34]

(b) lamellar microstructure[38]

(c) mixed lamellar/irregular microstructure[39]


铸态共晶高熵合金的力学性能不仅取决于共晶两相的组成,也与共晶形貌的调控密切相关。因fcc/B2共晶体系兼具良好的室温拉伸性能、疲劳寿命和抗氧化性能[37,42~44],其组织/性能调控相关的研究最多。针对fcc/B2共晶高熵合金体系,一方面可以通过调控凝固过程以改善共晶组织形貌和力学性能。例如,通过定向凝固技术获得排列一致的片层组织以抑制垂直拉伸方向的裂纹扩展[45~48],典型组织如图4a[48]所示;通过增材制造技术控制扫描和冷却速率能够显著细化晶粒[49,50],进一步借助重熔能够使沉积态组织等轴化,从而获得具有各向同性的组织[51],如图4b[50]c[51]所示。另一方面,fcc/B2共晶高熵合金凝固后的组织可以通过热机械处理进一步进行优化。热机械处理有效消除了铸造过程中产生的偏析和缺陷,同时引入了固溶强化、细晶强化、位错强化、析出强化四大传统强化机制。此外,通过调控热机械处理中的变形和退火工艺,可以获得丰富的再结晶组织,例如等轴超细晶结构、异质层片结构、相选择再结晶组织等[52~55],如图4d~f[52~54]所示。这些再结晶组织赋予了合金更为优异的力学性能。

图4

图4   多种工艺调控下的共晶高熵合金微观组织[48,50~54]

Fig.4   Microstructures of EHEAs tailored by various processing methods

(a) BSE image, EBSD phase, and Inverse pole figures (IPFs) of the directionally solidified Al19Fe20Co20Ni41 EHEA, showing a herringbone-like eutectic microstructure (BEC—branched eutectic colonies, AEC—aligned eutectic colonies)[48]

(b) EBSD IPF map of as-printed AlCoCrFeNi2.1 EHEA, showing ultrafine nanolamellar eutectic colonies with different crystallographic orientations (Inset shows the EBSD phase map)[50]

(c) EBSD phase map of the anomalous eutectic structure in remelted additive manufactured Ni32Co30Cr10Fe10Al18 EHEA[51]

(d) EBSD phase map of equiaxed ultrafine-grained structure in the 90% cold-rolled AlCoCrFeNi2.1 EHEA after isothermal annealing[53]

(e) SEM image and EBSD phase map of the AlCoCrFeNi2.1 EHEA cold-rolled by 84%-86% followed by non-isothermally annealing, showing heterogeneous duplex microstructure consisting of lamellar and ultrafine-grained structure[52]

(f) IPFs of the phase-selectively recrystallized Ni30Co30Cr10Fe10Al18W2 EHEA, showing the microstructure with a fully recrystallized fcc phase embedded in the skeleton of a B2 phase[54]


基于凝固组织调控的fcc/B2共晶高熵合金性能优化策略已经得到广泛的探索。最初报道的AlCoCrFeNi2.1共晶高熵合金以真空感应熔炼和浇铸的方式制造,抗拉强度接近1000 MPa,延伸率大于25%[13]。真空电弧熔炼与铜模铸造技术能够实现更高的熔体纯净度和冷却速率,有效细化了共晶片层,可以提升AlCoCrFeNi2.1合金抗拉强度至1200 MPa[14]。通过定向凝固调控共晶形貌可进一步提升共晶高熵合金的力学性能。研究[45]表明,随着抽拉速率的增加,AlCoCrFeNi2.1合金微观组织由层状共晶向胞状共晶转变,在60 μm/s的抽拉速率下局部出现枝-共晶凝固组织,其沿定向凝固方向的拉伸塑性增至37%。Shi等[48]增加抽拉速率至250 μm/s,制备出的“鱼骨状”共晶组织能够有效促进微裂纹的均匀形核,结合fcc相优异的裂纹钝化能力,有助于避免裂纹的灾难性扩展,从而使Al19Fe20Co20Ni41合金塑性提升了3倍,如图5a[48]所示。

图5

图5   具有不同微观组织的共晶高熵合金的力学性能[48,50~54]

Fig.5   Mechanical properties of EHEAs with different microstructures

(a) directionally solidified Al19Fe20Co20Ni41 EHEA with herringbone-like microstructure (Inset shows the strain-hardening rate curves. MDIH and MBIH refer to multi-slip dislocation-induced hardening and microband-induced hardening, respectively; εU—uniform strain; σy—yield strength of Al19Fe20Co20Ni41 EHEA; σUTS—ultimate tensile strength of Al19Fe20Co20Ni41 EHEA)[48]

(b) as-printed and annealed AlCoCrFeNi2.1 EHEA with ultrafine nanolamellar structure (Inset shows the schematic of a dogbone-shaped specimen under tensile loading. σu—ultimate tensile strength of AlCoCrFeNi2.1 EHEA; σ0.2—yield strength of AlCoCrFeNi2.1 EHEA)[50]

(c) additive manufactured Ni32Co30Cr10Fe10Al18 EHEA with anomalous eutectic structure[51]

(d) ultrafine-grained AlCoCrFeNi2.1 EHEA (CR—cold rolling)[53]

(e) heterogeneous-grained AlCoCrFeNi2.1 EHEA (Inset shows the loading-unloading-reloading behavior of the DPHL700 and the as-cast EHEA, DPHL—dual-phase heterogeneous lamella, UFG EHEA—ultrafine-grain EHEA, CH EHEA—complex and hierarchical EHEA)[52]

(f) phase-selectively recrystallized Ni30Co30Cr10Fe10Al18W2 EHEA (AC—as-cast, FR—fully recrystallization, PSR—phase-selective recrystallization)[54]


较之于定向凝固,增材制造技术涉及更大的温度梯度和更快的冷却速率,能够在共晶高熵合金中产生更为细小的组织。定向能量沉积和选区激光熔化是增材制造的2种主要工艺[56]。Ren等[50]通过选区激光熔化将AlCoCrFeNi2.1合金的片层厚度细化至200 nm以下,可使屈服强度提升至1.3 GPa,且保持14%的优异均匀延伸率,如图5b[50]所示。Zhou等[51]在Ni32Co30Cr10Fe10Al18共晶高熵合金中通过沉积过程中重熔诱导的柱状晶-等轴晶转变(CET)促进了等轴反常共晶组织的形成,赋予了合金优异的各向同性力学性能,如图5c[51]所示。增材制造技术凭借其直接成型的优势,加之对力学性能的大幅提升作用,预计未来将持续推动高强高韧共晶高熵合金的研究和发展。

热机械处理在共晶高熵合金组织/性能调控方面也取得了一系列重要进展。如图5d[53]所示,通过在大变形量冷轧后进行等温退火,可获得具有等轴超细晶的两相组织,使AlCoCrFeNi2.1合金强度得以大幅度提升[53,55]。而通过中温轧制能够调控出同时包含等轴和层片组织的异质结构共晶高熵合金,有利于促进异质变形诱导强化,其性能优于两相完全等轴化的合金[57]。Shi等[52]将冷轧84%~86%的AlCoCrFeNi2.1共晶高熵合金在660~740 ℃之间进行非等温退火,使两相发生再结晶的同时保留了层片结构,赋予了合金优异的抗裂纹扩展能力和异质强化效应,实现了合金强度与塑性的同时提升,其力学性能如图5e[52]所示。利用fcc/B2两相的再结晶驱动力差异,Wu等[54]提出了一种全新的选相再结晶工艺,获得了由骨架状B2相和镶嵌在其中的再结晶fcc相组成的混合组织。选相再结晶组织充分激发了两相合金的协调变形和加工硬化能力,使共晶高熵合金的均匀延伸率达到30%,如图5f[54]所示。在此基础上耦合预变形时效工艺进一步调控析出相密度以及位错组态,能够将抗拉强度提升至2 GPa以上。

3 共晶高熵合金应用探索与大规模制备

迄今为止,共晶高熵合金已经在多个领域展露出独特的性能。fcc/Laves、bcc/B2共晶高熵合金具有高硬度和良好的耐磨性能[58,59],但由于其塑性的限制,针对这些合金体系的工业生产和应用环境方面的评估较为有限[21,60]。fcc/B2共晶高熵合金在宽温域下表现出优异的力学性能和良好的热稳定性,是最有潜力实现工业化应用的高熵合金体系[40,61,62]。近年来,针对fcc/B2共晶高熵合金潜在的工业化应用背景,一些性能研究和环境评估测试迅速开展起来。首先,fcc/B2共晶高熵合金在室温静态单轴拉伸下具有优异的强塑性结合[14],并且在动态载荷条件下表现出明显的应变速率敏感性和稳定的应变硬化,无绝热剪切带产生[63]。随着温度的降低,其静态抗拉强度显著增加的同时塑性无明显退化,甚至在77 K下也未发生韧-脆转变[64]。此外,fcc/B2共晶高熵合金具有优异的抗NaCl腐蚀性能。实验结果[65]表明,AlCoCrFeNi2.1合金中富Cr的fcc相通过形成钝化膜提高了其在NaCl溶液中的耐腐蚀性能,而B2相内富Cr的bcc析出相则提高了B2相上富Al钝化膜的稳定性。这些特性使其在海洋领域具有广阔的应用前景,比如用于制造破冰船螺旋桨。fcc/B2共晶高熵合金具有微米尺度自生复合的特性,并结合了共晶相内纳米析出相的强化效应,这使其在耐磨材料领域展现出一定的潜力[66]。苗军伟等[67]采用电磁悬浮熔炼和直接铸造的方法制备了公斤级AlCr1.3TiNi2共晶高熵合金,其高温力学性能稳定,磨损率低于GH4169合金。通过激光重熔与热处理对AlCoCrFeNi2.1合金进行表面改性,其显微硬度可提高至433 HV,磨损率降至仅2.7 × 10-5 mm3/(N·m)[68]

在高温性能方面,定向凝固的AlCoCrFeNi2.1合金在700 ℃拉伸时具有630 MPa的良好强度,在600~800 ℃的宽温域中没有出现中温脆性[61]。通过B的微合金化,Ni30Co30Cr10Fe10Al18W2合金在700 ℃下的抗拉强度大幅提升至1100 MPa,800 ℃下抗拉强度达581 MPa,与Inconel 718高温合金相当[33]。此外,高熵合金的缓慢扩散效应使其具有良好的热稳定性[69],而共晶高熵合金中较多的Al和Cr元素更是赋予了其突出的高温抗氧化特性[44,70],从而保证了高温下长期服役的可靠性。结合自身低密度的优势,fcc/B2共晶高熵合金未来可能用于制造航空航天耐高温部件,如火箭推进器壳体、尾喷管、蒙皮、抗氧化涂层等。近来,fcc/B2共晶高熵合金优异的抗Pb-Bi腐蚀能力也得到了验证。黄赟浩等[71]研究表明,Al17Cr10Fe37Ni36合金在500~600 ℃的Pb-Bi饱和氧环境下可以形成致密而稳定的Fe-Cr-Al-O氧化膜,显著阻碍了液态Pb-Bi向基体的扩散和溶解。相比于传统的铁素体/马氏体钢和奥氏体不锈钢,该合金在高温Pb-Bi环境中更为稳定,有望成为液态Pb-Bi热工领域的新一代结构材料。除作为结构材料具备的性能以外,近年来功能性质方面的探索为共晶高熵合金提供了一个全新的应用方向。Han等[72]通过选择性蚀刻Ni30Co30Cr10Fe10Al18W2合金,制备了一种具有高析氢反应活性和析氧反应活性的多孔高熵合金电极,预示其有望成为自支撑高稳定性的催化材料。

基于以上分析,fcc/B2共晶高熵合金在应用端展现出的各类优势将加速其在产业界的推广应用,这也对其大规模制备提出了需求。首先,共晶高熵合金在铸造和焊接方面的优势为其大规模的工业应用提供了基本保障[73~75]。共晶高熵合金本身具有结晶温度间隔小、补缩好的凝固特性,特别适合制备大型铸件。目前,已经成功制备真空感应浇铸的吨级共晶高熵合金铸锭,如图6a所示。在此基础上通过锻造、轧制可制备出如图6b所示的大规格板材,且大型板材的焊接性能评估也正在进行当中。此外,共晶高熵合金已被用于开发具有较复杂结构的大型铸件,铸造出了百公斤级的叶轮,如图6c所示。现阶段,共晶高熵合金已经具备了工业化应用的材料加工制备雏形。

图6

图6   共晶高熵合金工业化制备示例

Fig.6   Examples of industrial production of EHEA

(a) ton-class EHEA ingot prepared by vacuum induction melting

(b) 200 mm wide cold-rolled sheet

(c) large marine propeller


4 结论与展望

共晶高熵合金是一类极具应用前景的新型高性能金属材料。共晶高熵合金发展的十年间,其成分设计、组织/性能调控、应用探索和制备技术等方面都取得了重要的进展。共晶高熵合金的合金设计方案已经趋于成熟,大量数据的积累使得机器学习开发高性能共晶高熵合金成为可能。可以预见,随着相关基础研究和应用研究的不断深入,共晶高熵合金在航空、航天、海洋、能源等领域都有着广阔的应用前景。目前,共晶高熵合金的力学性能已经通过增材制造、热机械处理等工艺得到显著提升。工程应用端的需求催生了共晶高熵合金的大规模制备。下一阶段,需要进一步开拓应用端的评估测试,并结合工业化生产有效推动未来共晶高熵合金的应用。然而,尽管许多共晶高熵合金表现出了优异的性能,但其作为一种新型金属结构材料,还存在一些问题需要更进一步的深入研究。

(1) 虽然共晶高熵合金存在诸多性能优势,但目前其成分探索仍然是较为困难的。共晶高熵合金由多组元合金元素组成,理论上存在无数个共晶成分。为了寻找新的共晶高熵合金体系,研究者需要开发具有普适性的共晶高熵合金设计方法。此外,由于许多共晶高熵合金中含有Co等昂贵元素,如何在保持其优异性能的同时实现低密度化和低成本化也是当下成分设计需要面临的挑战。目前,依靠物理模型并结合机器学习是共晶高熵合金成分设计的一个发展趋势,极大地加速了共晶高熵合金的开发速度。结合合金元素对共晶高熵合金微观组织及力学性能的影响规律,有助于实现共晶高熵合金成分的针对性设计。

(2) 由于共晶高熵合金所含元素及相组成较为复杂,相关的强韧化机理研究仍处于初期阶段。对于如何基于强韧化机理快速设计合适的热机械处理工艺,仍然缺乏系统的理论和实验指导。此外,单轴准静态力学性能只是合金性能的冰山一角,对抗氧化性能、相稳定性、冲击性能、疲劳性能、蠕变性能等综合性能的研究亟需完善。因此,未来研究的重点和难点之一是通过合理的成分设计和加工工艺,最大限度地优化共晶高熵合金的微观组织和综合性能。

(3) 合金的商业化过程离不开工业的大规模制备,共晶高熵合金虽已表现出巨大的应用潜力,但目前仍集中在实验室研究阶段,如何进行大规模的生产制备是其走向实际应用过程中必须研究和解决的问题。因此,共晶高熵合金的热变形行为和机械加工性能需要进行系统性的研究,例如建立基于共晶高熵合金物理性质的多应变路径弹塑性力学本构关系、复杂应力场和温度场下的静态/动态再结晶模型等。此外,增材制造作为近年来迅速发展的新技术,如何将其与共晶高熵合金更好地融合起来,实现先进材料与先进制备技术的相辅相成,从而实现应用优势的最大化也是未来研究的重点。

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Microstructure and mechanical properties of AlCo x CrFeNi3 - x eutectic high-entropy-alloy system

[J]. J. Alloys Compd., 2020, 823: 153886

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Wu Q F, Wang Z J, Zheng T, et al.

A casting eutectic high entropy alloy with superior strength-ductility combination

[J]. Mater. Lett., 2019, 253: 268

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Shukla S, Wang T H, Cotton S, et al.

Hierarchical microstructure for improved fatigue properties in a eutectic high entropy alloy

[J]. Scr. Mater., 2018, 156: 105

Lu J, Zhang H, Chen Y, et al.

Y-doped AlCoCrFeNi2.1 eutectic high-entropy alloy with excellent oxidation resistance and structure stability at 1000 oC and 1100 oC

[J]. Corros. Sci., 2021, 180: 109191

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Wang L, Yao C L, Shen J, et al.

Microstructures and room temperature tensile properties of as-cast and directionally solidified AlCoCrFeNi2.1 eutectic high-entropy alloy

[J]. Intermetallics, 2020, 118: 106681

[本文引用: 2]

Jiang X, Li Y, Shi P J, et al.

Synergistic control of microstructures and properties in eutectic high-entropy alloys via directional solidification and strong magnetic field

[J]. J. Mater. Res. Technol., 2024, 28: 4440

Wischi M, Campo K N, Starck L F, et al.

Microstructure and mechanical behavior of the directionally solidified AlCoCrFeNi2.1 eutectic high-entropy alloy

[J]. J. Mater. Res. Technol., 2022, 20: 811

Shi P J, Li R G, Li Y, et al.

Hierarchical crack buffering triples ductility in eutectic herringbone high-entropy alloys

[J]. Science, 2021, 373: 912

DOI      PMID      [本文引用: 8]

In human-made malleable materials, microdamage such as cracking usually limits material lifetime. Some biological composites, such as bone, have hierarchical microstructures that tolerate cracks but cannot withstand high elongation. We demonstrate a directionally solidified eutectic high-entropy alloy (EHEA) that successfully reconciles crack tolerance and high elongation. The solidified alloy has a hierarchically organized herringbone structure that enables bionic-inspired hierarchical crack buffering. This effect guides stable, persistent crystallographic nucleation and growth of multiple microcracks in abundant poor-deformability microstructures. Hierarchical buffering by adjacent dynamic strain-hardened features helps the cracks to avoid catastrophic growth and percolation. Our self-buffering herringbone material yields an ultrahigh uniform tensile elongation (~50%), three times that of conventional nonbuffering EHEAs, without sacrificing strength.Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

Guo Y N, Su H J, Zhou H T, et al.

Unique strength-ductility balance of AlCoCrFeNi2.1 eutectic high entropy alloy with ultra-fine duplex microstructure prepared by selective laser melting

[J]. J. Mater. Sci. Technol., 2022, 111: 298

[本文引用: 1]

Ren J, Zhang Y, Zhao D X, et al.

Strong yet ductile nanolamellar high-entropy alloys by additive manufacturing

[J]. Nature, 2022, 608: 62

[本文引用: 8]

Zhou K X, Li J J, Wu Q F, et al.

Remelting induced fully-equiaxed microstructures with anomalous eutectics in the additive manufactured Ni32Co30Cr10Fe10Al18 eutectic high-entropy alloy

[J]. Scr. Mater., 2021, 201: 113952

[本文引用: 6]

Shi P J, Ren W L, Zheng T X, et al.

Enhanced strength-ductility synergy in ultrafine-grained eutectic high-entropy alloys by inheriting microstructural lamellae

[J]. Nat. Commun., 2019, 10: 489

DOI      PMID      [本文引用: 6]

Realizing improved strength-ductility synergy in eutectic alloys acting as in situ composite materials remains a challenge in conventional eutectic systems, which is why eutectic high-entropy alloys (EHEAs), a newly-emerging multi-principal-element eutectic category, may offer wider in situ composite possibilities. Here, we use an AlCoCrFeNi EHEA to engineer an ultrafine-grained duplex microstructure that deliberately inherits its composite lamellar nature by tailored thermo-mechanical processing to achieve property combinations which are not accessible to previously-reported reinforcement methodologies. The as-prepared samples exhibit hierarchically-structural heterogeneity due to phase decomposition, and the improved mechanical response during deformation is attributed to both a two-hierarchical constraint effect and a self-generated microcrack-arresting mechanism. This work provides a pathway for strengthening eutectic alloys and widens the design toolbox for high-performance materials based upon EHEAs.

Wani I S, Bhattacharjee T, Sheikh S, et al.

Tailoring nanostructures and mechanical properties of AlCoCrFeNi2.1 eutectic high entropy alloy using thermo-mechanical processing

[J]. Mater. Sci. Eng., 2016, A675: 99

[本文引用: 4]

Wu Q F, He F, Li J J, et al.

Phase-selective recrystallization makes eutectic high-entropy alloys ultra-ductile

[J]. Nat. Commun., 2022, 13: 4697

DOI      PMID      [本文引用: 7]

Excellent ductility is crucial not only for shaping but also for strengthening metals and alloys. The ever most widely used eutectic alloys are suffering from the limited ductility and losing competitiveness among advanced structural materials. Here we report a distinctive concept of phase-selective recrystallization to overcome this challenge for eutectic alloys by triggering the strain hardening capacity of the duplex phases completely. We manipulate the strain partitioning behavior of the two phases in a eutectic high-entropy alloy (EHEA) to obtain the phase-selectively recrystallized microstructure with a fully recrystallized soft phase embedded in the skeleton of a hard phase. The resulting microstructure fully releases the strain hardening capacity in EHEA by eliminating the weak boundaries. Our phase-selectively recrystallized EHEA achieves a high ductility of ∼35% uniform elongation with true stress of ∼2 GPa. This concept is universal for various duplex alloys with soft and hard phases and opens new frontiers for traditional eutectic alloys as high-strength metallic materials.© 2022. The Author(s).

Xiong T, Zheng S J, Pang J Y, et al.

High-strength and high-ductility AlCoCrFeNi2.1 eutectic high-entropy alloy achieved via precipitation strengthening in a heterogeneous structure

[J]. Scr. Mater., 2020, 186: 336

[本文引用: 2]

Lu Y P, Wu X X, Fu Z H, et al.

Ductile and ultrahigh-strength eutectic high-entropy alloys by large-volume 3D printing

[J]. J. Mater. Sci. Technol., 2022, 126: 15

DOI      [本文引用: 1]

3D printing of high-strength alloys enables efficient manufacturing of complex metallic components. Yet, the as-built parts are often characterized by unsatisfied ductility due to micro-defects, requiring additional heat treatment to optimize the structure before in-site applications. The post heat-processing, however, often changes the shape of the printed parts, deteriorating the quality of the printed components. In addition, many printed large-scale alloy parts with complex shapes are difficult to be processed by hot isostatic pressing. This requires that the alloys can be printed with good strength and ductility without the necessity of additional thermal processing. Here, we show that excellent ductility and ultrahigh strength can be achieved in a eutectic high-entropy alloy (EHEA) by large-volume 3D printing. The as-printed EHEA has a tensile yield strength of 1040 MPa, and a total elongation of 24%, as well as superior corrosion resistance in seawater environment. The excellent combination of properties outperforms that of all other existing metallic materials. Note that these astonishing properties are from specimens directly after 3D printing without any subsequent heat treatment and hot isostatic pressing. The exceptional mechanical properties are mainly ascribed to the fine lamella spacing in the composite structure consisting of face-centered cubic matrix and B2 precipitates, which renders high resistance for dislocation movement and extends work hardening capability. The EHEA printed in large volume without post processing thus shows high applicability for mass-production at an industrial scale.

Reddy S R, Yoshida S, Sunkari U, et al.

Engineering heterogeneous microstructure by severe warm-rolling for enhancing strength-ductility synergy in eutectic high entropy alloys

[J]. Mater. Sci. Eng., 2019, A764: 138226

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Wen X, Cui X F, Jin G, et al.

In-situ synthesis of nano-lamellar Ni1.5CrCoFe0.5Mo0.1Nb x eutectic high-entropy alloy coatings by laser cladding:Alloy design and microstructure evolution

[J]. Surf. Coat. Technol., 2021, 405: 126728

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Xiao Y K, Chang X P, Peng X H.

Low-density NiAlFeCrMoV eutectic high-entropy alloys with excellent mechanical and wear properties

[J]. J. Mater. Res. Technol., 2022, 21: 4908

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Chen X, Qi J Q, Sui Y W, et al.

Effects of aluminum on microstructure and compressive properties of Al-Cr-Fe-Ni eutectic multi-component alloys

[J]. Mater. Sci. Eng., 2017, A681: 25

[本文引用: 1]

Zhang Y L, Li J G, Wang X G, et al.

The interaction and migration of deformation twin in an eutectic high-entropy alloy AlCoCrFeNi2.1

[J]. J. Mater. Sci. Technol., 2019, 35: 902

DOI      [本文引用: 2]

An eutectic high-entropy alloy consisting Al, Co, Cr, Fe and Ni elements was prepared by vacuum directional solidification technology. The alloy exhibits excellent comprehensive mechanical performance during tension at temperature range of 600-700 °C. The microstructure reveals the intersection of twin-twin is the prevailing deformation mechanism and the twins play a dual role in strengthening and toughening the alloy in the thermomechanical process. The deformation twin variants I and Π were formed by the edge dislocation 112ˉ and the mixed dislocation 211ˉ on the {111} crystal planes, respectively. Besides, the dislocation jogs and kinks caused by twin intersection on the slip planes can strengthen the alloy, which may contribute to the high strength (the tensile strengths at the 600° and 700° tensile tests are respectively780 MPa and 630 MPa.). Moreover, the coherent twin boundary migration has the function of coordinating deformation and contributes to the high ductility of the alloy.

Li Y, Shi P J, Wang M Y, et al.

Unveiling microstructural origins of the balanced strength-ductility combination in eutectic high-entropy alloys at cryogenic temperatures

[J]. Mater. Res. Lett., 2022, 10: 602

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Li J S, Zhou J, Liu Y F, et al.

Microstructural origins of impact resistance of AlCoCrFeNi2.1 eutectic high-entropy alloy

[J]. Mater. Sci. Eng., 2024, A890: 145921

[本文引用: 1]

Bhattacharjee T, Zheng R X, Chong Y, et al.

Effect of low temperature on tensile properties of AlCoCrFeNi2.1 eutectic high entropy alloy

[J]. Mater. Chem. Phys., 2018, 210: 207

[本文引用: 1]

Duan X T, Han T Z, Guan X, et al.

Cooperative effect of Cr and Al elements on passivation enhancement of eutectic high-entropy alloy AlCoCrFeNi2.1 with precipitates

[J]. J. Mater. Sci. Technol., 2023, 136: 97

[本文引用: 1]

Dong J X, Wu H X, Chen Y, et al.

Study on self-lubricating properties of AlCoCrFeNi2.1 eutectic high entropy alloy with electrochemical boronizing

[J]. Surf. Coat. Technol., 2022, 433: 128082

[本文引用: 1]

Miao J W, Wang M L, Zhang A J, et al.

Tribological properties and wear mechanism of AlCr1.3TiNi2 eutectic high-entropy alloy at elevated temperature

[J]. Acta Metall. Sin., 2023, 59: 267

[本文引用: 1]

苗军伟, 王明亮, 张爱军 .

AlCr1.3TiNi2共晶高熵合金的高温摩擦学性能及磨损机理

[J]. 金属学报, 2023, 59: 267

DOI      [本文引用: 1]

采用电磁悬浮熔炼+直接铸造的方法制备了千克级的AlCr1.3TiNi2共晶高熵合金,借助TEM、APT等表征手段分析了该合金的微观组织与成分分布,使用HT-1000摩擦试验机对比研究了该合金与GH4169镍基高温合金的高温摩擦学性能。结果表明:该共晶高熵合金具有超细的层片状共晶组织(层片间距约350 nm),其共晶两相为晶格错配度只有约2%的bcc相与L21相,L21相中还存在大量的纳米析出相;≤ 600℃时,共晶高熵合金的磨损机理以磨粒磨损为主,其磨损率均低于GH4169合金;800℃时,共晶高熵合金的磨痕表面塑性变形加剧,其摩擦系数明显高于GH4169合金,但2者的磨损率相差不大。GH4169合金高温耐磨性的提高得益于其磨损表面氧化物膜的形成,而共晶高熵合金出色的耐磨性主要与其良好的高温组织稳定性及力学性能有关。

Miao J W, Yao H W, Wang J, et al.

Surface modification for AlCoCrFeNi2.1 eutectic high-entropy alloy via laser remelting technology and subsequent aging heat treatment

[J]. J. Alloys Compd., 2022, 894: 162380

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Peng P, Feng X N, Li S Y, et al.

Effect of heat treatment on microstructure and mechanical properties of as-cast AlCoCrFeNi2.1 eutectic high entropy alloy

[J]. J. Alloys Compd., 2023, 939: 168843

[本文引用: 1]

Lu J, Zhang H, Li L, et al.

Y-Hf Co-doped AlCoCrFeNi2.1 eutectic high-entropy alloy with excellent oxidation and spallation resistance under thermal cycling conditions at 1100 oC and 1200 oC

[J]. Corros. Sci., 2021, 187: 109515

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Huang Y H, Wang J B, Wang Z J, et al.

Corrosion behavior of high strength AlCrFeNi multi-principal-component alloy in lead-bismuth alloy

[J]. Nucl. Power Eng., 2023, 44(S1): 137

[本文引用: 1]

黄赟浩, 王健斌, 王志军 .

铅铋合金环境中高强AlCrFeNi多主元合金的腐蚀行为

[J]. 核动力工程, 2023, 44(S1): 137

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Han X, Chen Q, Chen Q X, et al.

Eutectic dual-phase microstructure modulated porous high-entropy alloys as high-performance bifunctional electrocatalysts for water splitting

[J]. J. Mater. Chem., 2022, 10A: 11110

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Li P, Sun H T, Wang S, et al.

Rotary friction welding of AlCoCrFeNi2.1 eutectic high entropy alloy

[J]. J. Alloys Compd., 2020, 814: 152322

[本文引用: 1]

Shen J J, Agrawal P, Rodrigues T A, et al.

Gas tungsten arc welding of as-cast AlCoCrFeNi2.1 eutectic high entropy alloy

[J]. Mater. Des., 2022, 223: 111176

Li P, Sun H T, Dong H G, et al.

Microstructural evolution, bonding mechanism and mechanical properties of AlCoCrFeNi2.1 eutectic high entropy alloy joint fabricated via diffusion bonding

[J]. Mater. Sci. Eng., 2021, A814: 141211

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