材料研究学报, 2020, 34(7): 535-544 DOI: 10.11901/1005.3093.2019.557

研究论文

高熵合金FeCoNiTi的微观组织演变和强韧化行为

刘怡1, 徐康1, 涂坚,1,2, 黄灿1, 吴玮1, 谭力1, 张琰斌1, 尹瑞森3, 周志明1,2

1.重庆理工大学材料科学与工程学院 重庆 400054

2.重庆理工大学 重庆市模具技术重点实验室 重庆 400054

3.重庆大学航天航空学院 重庆 400044

Microstructure Evolution and Strength-ductility Behavior of FeCoNiTi High-entropy Alloy

LIU Yi1, XU Kang1, TU Jian,1,2, HUANG Can1, WU Wei1, TAN Li1, ZHANG Yanbin1, YIN Ruisen3, ZHOU Zhiming1,2

1.School of Materials Science and Engineering, Chongqing University of Technology, Chongqing 400054, China

2.Chongqing Municipal Key Laboratory of Institutions of Higher Education for Mould Technology, Chongqing University of Technology, Chongqing 400054, China

3.School of Aerospace Engineering, Chongqing University, Chongqing 400030, China

通讯作者: 涂坚,副教授,tujian@cqut.edu.cn,研究方向为高熵合金的组织与性能

责任编辑: 黄青

收稿日期: 2019-12-02   修回日期: 2020-01-18   网络出版日期: 2020-07-25

基金资助: 重庆市基础与前沿研究计划.  2017jcyjAX0381
重庆市教委科技研究项目.  KJQN201801139
国家博士面上资助.  2018M632250

Corresponding authors: TU Jian, Tel: (023)62563178, E-mail:tujian@cqut.edu.cn

Received: 2019-12-02   Revised: 2020-01-18   Online: 2020-07-25

Fund supported: Basic and Advanced Research Project of CQ CSTC.  2017jcyjAX0381
Science and Technology Research Program of Chongqing Municipal Education Commissio.  KJQN201801139
China Postdoctoral Science Foundation Funded Project.  2018M632250

作者简介 About authors

刘怡,女,1996年生,硕士生

摘要

使用热力学软件设计了一种新型双相高熵合金(FeCoNiTi),利用真空电弧熔炼和热处理制备出FeCoNiTi高熵合金块体材料。表征结果表明,FeCoNiTi高熵合金由层状结构的Laves相和魏氏体板条FCC相组成。在室温下FeCoNiTi高熵合金具有良好的综合力学性能(抗压强度σb=2.08 GPa,压缩应变ε=20.3%)。高强度来自“硬”Laves相(层状结构)的强化,而“软”FCC相(魏氏体板条)中的位错滑移和变形孪晶提供塑性。

关键词: 金属材料 ; 高熵合金 ; 强韧化 ; 双相组织 ; 魏氏体板条

Abstract

A new type of dual-phase high-entropy alloy (FeCoNiTi) was designed by means of thermodynamic software and then block material of FeCoNiTi high-entropy alloy was prepared via vacuum arc smelting and then heat treatment. Characterization results demonstrate that the as-homogenized FeCoNiTi alloy presents dual-phase microstructure composed of the lamellar structure (hexagonal close packed (Laves) phase) and the Widmanstätten laths (face-centered cubic (FCC) phase). The FeCoNiTi alloy shows excellent comprehensive property at room temperature with compressive strength σb=2.08 GPa and compression strain ε=20.3%. The high strength can mainly be attributed to the hard Laves phase (lamellar structure) strengthening; while dislocation slip and deformation twin in the soft FCC phase (Widmanstätten laths) provide the ductility.

Keywords: metallic materials ; high entropy alloy ; strength-ductility ; dual-phase ; widmanstätten laths

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本文引用格式

刘怡, 徐康, 涂坚, 黄灿, 吴玮, 谭力, 张琰斌, 尹瑞森, 周志明. 高熵合金FeCoNiTi的微观组织演变和强韧化行为. 材料研究学报[J], 2020, 34(7): 535-544 DOI:10.11901/1005.3093.2019.557

LIU Yi, XU Kang, TU Jian, HUANG Can, WU Wei, TAN Li, ZHANG Yanbin, YIN Ruisen, ZHOU Zhiming. Microstructure Evolution and Strength-ductility Behavior of FeCoNiTi High-entropy Alloy. Earth Science[J], 2020, 34(7): 535-544 DOI:10.11901/1005.3093.2019.557

现代工业的发展对金属材料性能的要求不断提高,以一种或两种金属元素为主的传统合金材料不能满足要求。因此,有必要研制新型合金材料。2004年Yeh首次提出“多主元合金”材料的设计概念,并将其命名为高熵合金(High-entropy alloys, HEAs)[1]。高熵合金打破传统合金以一种或两者元素为主的设计理念而是多种元素的混合,各元素的百分比为5%~35%,形成单相固溶体。高熵合金具有许多优异的性能,例如:高强度,高室温韧性,以及高耐磨性,耐蚀性和热稳定性[2,3,4,5,6]。但是怎样在实现合金高强度的同时保证其延展性,一直是研究者们的追求目标。合金材料的强韧化机制,有固溶强化[7],细晶强化[8,9],弥散强化[10],相变诱导塑性机制[11,12]等。为了优化高熵合金强韧化,可综合考虑上述机制。第一,对高熵合金进行退火、时效、轧制等工艺处理。例如,对AlCrFeNi2Ti0.5高熵合金进行退火处理后,其强度提高了600 MPa,压缩应变提高了2倍[13]。第二,在单相高熵合金基体中加入少量的金属元素析出第二相,以提高其强度。例如,在CoCrFeNi合金中加入微量Al和Ti并进行固溶和轧制处理,在γ基体中析出Ni3(Ti,Al)纳米晶使合金的屈服强度提高3~5倍[10]。第三,设计双相高熵合金。研究发现,单相固溶结构的高熵合金不如双相高熵合金具备综合的力学性能[9,12]。例如,单相FCC(Face-centered cubic, FCC)结构的高熵合金通常具有较好室温塑性和较低的强度[14],而单相体心立方结构(Body-centered cubic, BCC)高熵合金常具有较高的硬度和较低的塑性变形能力[15]。对此,Wang等[16]设计的有序BCC(B2)和无序BCC双相结构Al0.7CoCrFe2Ni高熵合金,具有较高的强度及塑性。另外,BCC+FCC双相NiFeCrMoW高熵合金的主要相结构由BCC转变为FCC时发生脆性到韧性的转变,使材料的塑性提高[17]。鉴于此,本文以单一FCC结构的FeCoNi作为基体材料,添加钛(Ti)原子形成FeCoNiTi双相高熵合金。大原子尺寸Ti原子的加入,有利于形成BCC和/或Laves结构[18]。根据晶体结构性质,FCC结构比较“软”,易滑移,可提供塑性;而Laves结构较“硬”,可提供强度。因此,本文在FeCoNiTi高熵合金中形成FCC+Laves双相组织结构,以期实现高熵合金强韧化。本文使用CALPHAD(CALculation of PHAse Diagram)热力学软件对FeCoNiTi高熵合金相结构进行初步预测,以期缩短实验周期,降低实验成本。使用电子背散射衍射(Electron Backscattered Diffraction)技术快速标定晶体材料大面积区域的逐点晶体学取向信息,重构出该区域的微观组织结构,可直观地观察到相组成和取向关系等信息,且统计性较好。鉴于此,本文使用EBSD测试手段表征形变过程的微观组织结构,以期揭示微观组织的演变规律。

1 实验方法

使用Thermo-Calc软件计算FeCoNi及FeCoNiTi高熵合金相组成随温度的变化情况。Themo-Calc是基于欧洲热力学研究小组Dinsdale等[19]在1991年发表的纯元素的吉布斯自由能-温度表达式,以及相关二元、三元数据的热力学数据库而建立的热力学计算模拟软件。

实验中用真空非自耗电弧熔炼炉制备等原子比FeCoNiTi高熵合金。先将高纯度(>99.5%)的金属粉末充分混合,并压成直径为10 mm、厚度为10 mm的圆柱体。将圆柱样放置水冷铜坩埚中在Ar气氛中进行熔炼,为了使合金成分分布均匀每个样品至少反复熔炼四次,熔炼完毕冷却后得到纽扣状铸态试样。在铸态试样上用电火花线切割得到ϕ4 mm×5 mm圆柱试样。随后在1273K对圆柱体样品进行保温4H的均质处理,得到均匀态试样。对该均匀态样品进行力学压缩实验,最后对均匀态样品进行单轴压缩变形(变形量为10%)得到形变态样品。

用光学显微镜(Optical Microscopy,OM)、X射线衍射仪(X-ray Diffraction,XRD)、扫描电子显微镜(Scanning Electron Microscope,SEM)和电子背散射衍射(Electron Back Scatter Diffraction,EBSD)对铸态、均匀态、形变态样品进行系统地微观组织结构表征。XRD测试,采用Cu靶,Kα射线λ=0.154 nm,其中管电压为40 kV,管电流为40 mA,扫描速率0.328°/s,扫描范围为20°~110°。EBSD观察面为圆柱样品的CD-RD面(CD:压缩方向,RD:径向方向)。依次用400#,800#,1500#,2500#水磨砂纸磨光观察面,然后用电解抛光制备EBSD试样。电解抛光液配比为10%乙酸+90%高氯酸,抛光温度控制在-30℃,抛光电压为20 V,抛光电流为0.3 A左右,抛光60 s后迅速取出后用流水冲洗腐蚀面,再用无水乙醇进行最终清洗,用冷风吹干后得到表面平整光亮的EBSD试样。

2 结果和分析

图1给出了FeCoNi和FeCoNiTi高熵合金中各相组成随温度变化的相图。由图1a可知,FeCoNi合金在620~1424℃温度区间内呈单一稳定的FCC相固溶体,在400~620℃呈FCC+BCC相结构的固溶体。Ti原子的半径较大,将其加入高熵合金体系中易形成BCC和/或Laves相结构,可提高材料的强度和硬度[18]。如图1b所示,Ti原子的加入使其相结构发生变化。在900~1030℃主要形成FCC+Laves+BCC三相结构,并出现少量的Ni3Ti金属间化合物。

图1

图1   FeCoNi和FeCoNiTi高熵合金的相组成随温度的变化

Fig.1   Fraction of stable phases as function of temperature calculated by CAPHAD for (a) FeCoNi and (b) FeCoNiTi


图2a给出了铸态FeCoNiTi高熵合金的金相图,可见呈典型的枝晶结构。在多主元合金中,如果某一元素的熔点明显低于其他元素,则在凝固过程中易出现树枝状的成分偏析[20]。对于FeCoNiTi 高熵合金,Ti的熔点(1941 K)比其他元素(Co、Fe和Ni)高得多。FeCoNiTi 高熵合金的凝固过程为枝晶凝固,因此铸态组织呈现枝晶形态(图2a)。图2b表明,均匀化热处理后初始态的枝晶组织消失,生成晶粒尺寸超过1 mm的FCC粗晶(晶界由图2b中的虚线描绘)。此外,在图2b中可观察到在粗晶组织内有大量板条相互交错组成的魏氏体结构。研究表明,过热的钢[21]、钛[22]、锆[22]和铝钛合金[23]在快速冷却过程中易形成魏氏体组织。类似地,FeCoNiTi在过热处理后生成魏氏体组织结构。

图2

图2   呈枝晶结构FeCoNiTi高熵合金铸态金的相图和显示粗晶组织和魏氏体板条的均匀态组织结构金相图

Fig.2   (a) the optical microscopy images of the as-cast FeCoNiTi HEA, revealing the nearly equiaxial dendrite structure; (b) the homogenized microstructure, revealing coarse grain boundary and Widmanstätten laths


图3为场发射扫描电镜拍摄均匀态样品的背散射电子图像。图3a表明,均匀态组织结构由层状结构和魏氏体板条共同组成。从图3b可见,魏氏体板条嵌在层状组织结构中。值得注意的是,魏氏体板条与层状结构之间呈现29.3°、62.8°和89.1°(由箭头指出)的取向差,与文献报道马氏体与层状结构之间的理论角度值[23](34.5°、63.6°和95°)接近。更有趣的是,在魏氏体板条中可观察到两种不同的形态特征,即条形板条(图3c)和三角形状(图3d)。条形板条的宽约100 nm,且条形板条之间完全平行(图3c)。在图3d中可观察到规则排列的,长宽尺寸较小的三角形状。此外,从图3b可见魏氏体板条三角排列的三个不同交角,即39.1°、55.8°和70.1°(由箭头标记),与文献的报道魏氏体板条之间的理论角度值(38.9°、56.3°和70.5°)非常接近[23]

图3

图3   均匀态FeCoNiTi高熵合金的背散射衍射图

Fig.3   Back-scattered electron images of the as-homogenized FeCoNiTi HEA (a) lamellar structure and Widmanstätten laths; (b) Widmanstätten laths showing misorientation of 29.3°, 62.8° and 89.1° (marked by arrows) with respect to the embedding lamellar structure, Widmanstätten laths with three different angles of intersection are revealed, i.e., 39.1°,55.8° and 70.1° (marked by arrows); two Widmanstätten laths showing two shapes: strip in (c) and triangle in (d)


图4为均匀态FeCoNiTi高熵合金的EBSD图。图4a~b表明均匀态的组织结构为层状结构和魏氏体板条。图4c表明该组织呈双相结构,蓝色和红色分别对应FCC和Laves(六方晶体结构)相,其比例分别为59.9%和40.1%。图4c中的内嵌图为均匀态FeCoNiTi高熵合金的XRD图谱。该图谱表明,FeCoNiTi高熵合金由FCC相和Laves相构成,与EBSD分析结果一致。但是,在EBSD及XRD实验表征结果里并没有观察到相图(图1b)中预测的Ni3Ti和BCC相结构。推测其原因是,在1273K形成的Ni3Ti相含量太低(0.82%)。BCC相未观察到的原因可能是:1)在1273K相变驱动力不足,难以达到平衡相组成;2)Thermo-Calc软件收录的数据不全,使模拟结果与实验结果出现误差。结合图4a和图4c可知,FCC相由魏氏体板条组成,Laves相则由层状结构组成。图4d对FCC相的{111}和{110}极图,以及Laves相的{0001}和{112¯0}极图进行了详细分析。如图4d中的三角符号可知,Laves相的{0001}基面与FCC相的四个{111}面之一完全重合,呈{0001}//{111}的取向关系。同时可观察到Laves相的[112¯0]晶带轴平行于FCC相[110]晶带轴,符合<112¯0>//<110>的取向关系。图4d表明,FeCoNiTi高熵合金中FCC相与Laves相之间存在Shoji-Nishiyama取向关系,即{0001}Laves//{111}FCC,<112¯0>Laves//<110>FCC。

图4

图4   背散射电子图、反极图、相图和XRD图谱

Fig.4   (a), (b) and (c) band contrast map, inverse pole figure and phase map, respectively. The inset shows X-ray diffraction patterns. Relationship between FCC and Laves phases: pole figure of FCC phase in (d), and pole figure of Laves phase in (e), revealing the S-N relationship between the Laves phase and its adjacent FCC phase in the white rectangle of (c)


图5给出了均匀态样品的两个典型的代表性区域,根据扫描电镜中的能谱分析(EDS)研究了元素在合金中的分布。魏氏体内部呈富Ni分布,而层状结构中Fe元素的浓度较高,Ni元素的浓度较低。层状结构区域(位置1和3)的点能谱分析(表1)证实,Ni元素的含量最低,Fe元素的含量最高。此外,由表1表明,在魏氏合金板条区域(位置2和4)含有丰富的Ni元素。因此,在均匀态的FeCoNiTi高熵合金中存在元素的富集,表明不同合金元素在魏氏体板条和层状结构中出现不同程度的偏聚。

图5

图5   两个代表性选区元素的分布

Fig.5   (a) and (b) shows the widmanstätten laths and lamellar structure


表1   层状结构(位置1和3)和魏氏体板条(位置2和4)的化学成分

Table 1  Chemical composition of lamellar structure (locations 1 and 3) and Widmanstätten laths (locations 2 and 4)

MicrostructureElements (%, atom fraction)
FeCoNiTi
Lamellar structureLocations 131.628.911.228.3
Locations 333.328.710.528.5
Widmanstätten lathsLocations 217.4127.232.4122.98
Locations 417.427.432.322.9

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图6a给出了FeCoNiTi高熵合金的压缩应力-应变曲线,可见室温工程应力-应变状态下其屈服强度为1.52 GPa,抗压强度为2.08 GPa,压缩应变为20.3%。图6b所示的FeCoNiTi 高熵合金压缩断口形貌,由解理面和韧窝组成。根据FCC相和Laves相结构性质推测:软FCC相在压缩过程中容纳更多的应力,进而形成韧窝断裂形貌;而硬Laves相的塑性变形能力有限,因此呈解理断裂形貌。为进一步验证该推测,对FeCoNiTi高熵合金进行形变处理,以研究其形变过程的微观组织演变机制。

图6

图6   FeCoNiTi高熵合金的压缩应力-应变曲线和断口形貌

Fig.6   (a) compressive stress-strain curve, (b) compressive fracture morphology of FeCoNiTi HEA


图7给出了形变态FeCoNiTi高熵合金的背散射电子图像。从图7a~b可见两种典型的形变组织:宽度非常细小的扭曲层状结构(图7c)和透镜状形变孪晶(图7d)。在形变过程中为了释放应力集中,层状结构在应力作用下发生扭曲(图7c)。同时,在应力作用下层状组织内部激活了形变孪晶(图7d)。形变孪晶的形成可降低该区域内位错滑移的平均自由程、提高其加工硬化能力,从而阻止该区域的进一步变形、使变形向变形程度较低的区域转移[24,25,26]。这一过程使材料发生均匀变形,进而推迟裂纹的产生。此外,形变孪晶扭曲是形变孪晶与位错间强烈的相互作用的结果,该过程能提高材料的加工硬化能力。

图7

图7   形变FeCoNiTi高熵合金的不同放大倍数SEM照片

Fig.7   SEM images under the different magnification for the as-deformed FeCoNiTi HEA; two typical types of deformation microstructure are detectable in (a) and (b); the distorted lamellar structure in (c); the lenticular twins in (d)


图8给出了形变FeCoNiTi高熵合金的EBSD图。图8a反极图中晶界线条(图8a中的黑色线条),显示出一个部分原始粗晶。在晶界图(Grain boundary, GB)中将两相邻晶粒取向差在3~15°范围的定义为小角度晶界(Low angle boundaries, LABs),大于15°为大角度晶界(High angle boundaries, HABs)(图8b),定义围绕<111>轴线方向偏转60°的特殊界面为形变孪晶界(Twin boundaries, TBs)。图8c~d分别给出了FCC相和Laves相的晶界取向分布图。在FCC相(图8c)中存在一定数量的小角度晶界,该晶界属于变形引起的位错界面。同时可观察到在FCC相存在较多60°<111>取向,表明形变孪晶被激活。此外,由图8c可知,FCC相内形变孪晶占比高于小角度晶界,说明在FCC相内的形变机制由形变孪晶主导。然而,Laves相内的形变机制由位错滑移主导。因此,在形变过程中FCC相和Laves相都有其相应的主导形变机制。

图8

图8   FeCoNiTi高熵合金形变态的EBSD图像

Fig.8   shows EBSD maps for the deformed FeCoNiTi HEA (a) IPF map showing two coarse grains; (b) grain boundary map showing low angle boundaries (LABs, marked by gray lines), high angle boundaries (HABs, marked by black lines). and twinning boundaries (TBs, marked by red lines); grain boundary misorientation statistical results of FCC phase and Laves phase in (c) and (d), respectively; (e) and (f) showing dual phase microstructure under higher magnification images: Laves phase (lamellar structure) embedded in FCC phase; (g) kernel average misorientation map showing the deformation behavior in FCC and Laves phases


图8e~g为形变微观结构的高倍EBSD图,包括背散射电子图(e)、相图(f)和KAM(Kernel average misorientation)图(g)。图8e~f进一步证实双相结构的存在,即Laves相(层状结构)和FCC相(魏氏体板条)。KAM值表示位错密度,蓝色为位错密度最低(<1°)的区域,中等位错密度用绿色表示,红色区域位错密度最高。FCC和Laves相内部的KAM值几乎都低于1°(图8g),表明在FCC相和Laves相内应变分布较为均匀,存在均匀的变形行为。由图8g可知,KAM值在相界(图8f中的白色轮廓)处较高,意味应变在相界面更为集中。因此,相界面可作为位错运动的阻碍,形成位错堆积。

3 讨论

克服合金强度-塑性失衡的有效方法,是设计“软”和“硬”双相组织结构。因此,本文从多组元固溶体的形成准则出发,并利用CALPHAD技术进行相结构预测,以设计双相结构高熵合金,最后用EBSD表征技术进行验证。从热力学性质出发,根据混合焓(Hmix)和价电子浓度(VEC)设计准则拟定了FeCoNiTi高熵合金:1)当混合焓接近0时合金元素易形成固溶体,混合焓越负则越容易形成金属间化合物[27,28];2)VEC8的合金易形成FCC单相结构,8>VEC6.87则易形成FCC+BCC双相组织结构[29]。从表2可知,Fe、Co、Ni间的混合焓近似0,易形成固溶体,而与Ti的混合焓较负易形成金属间化合物。计算结果表明,FeCoNiTi高熵合金的价电子浓度VEC=7.75,所以倾向于形成双相结构以满足形成双相结构的价电子浓度准则。除上述经验设计外,CALPHAD计算结果表明,在FeCoNi体系中加入Ti原子可在高温下形成FCC+BCC+Laves三相结构。从EBSD及XRD表征实验结果可知,FeCoNiTi高熵合金呈FCC+Laves双相结构。但是在实验表征上未标定出BCC相,可能与相变驱动力及Thermo-Calc数据库不完整有关。总之,FeCoNiTi高熵合金的相结构符合预期的“软”(FCC相)和“硬”(Laves相)的双相结构。

表2   使用Miedema模型计算的二元等原子合金的混合焓、Fe,Co、Ni、Ti的原子半径以及价电子浓度以及杨氏模量

Table 2  The enthalpy of mixing (ΔHmix, kJ mol-1) of binary equiatomic alloys calculated by Miedema's approach. The atom radius, valence electron concentrations (VEC) and Young’s modili of Fe, Co, Ni, Ti

ElementFeCoNiTi

Atom radius

/nm

VEC

Young's moduli

/GPa

Fe0-1-2-170.12148211
Co-00-280.12519209
Ni--0-350.124610200
Ti---00.14624116

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FeCoNiTi高熵合金的微观组织演变,如图9所示。在FeCoNiTi高熵合金由液态(图9a)凝固为固态的过程中,由于不存在固定的溶质和溶剂,各组元成分接近,成分过冷度高,易形成枝晶结构(图9b)。均匀化处理后,FeCoNiTi高熵合金形成魏氏体板条和层状组织的混合结构(图9c)。而且,魏氏体板条和层状组织间存在不同角度取向(图9c)。此外,具有条状结构和三角形状结构的魏氏体组织也具有不同角度取向(图9c)。在对均匀态样品进行形变处理后,可观察位错滑移及形变孪晶在FCC相内的激活(图9d),以及Laves相内存在的位错滑移(图9d)。同时,还可观察位错在FCC相和Laves相相界间的累积(图9d)。

图9

图9   FeCoNiTi高熵合金的微观组织演变

Fig.9   Microstructure evolution of FeCoNiTi HEA (a) Liquid, (b) As-cast, (c) As-homogenized, (d) Deformed


FeCoNiTi高熵合金的强化机制,包括固溶强化和界面强化,其中固溶强化受原子尺寸错配度,杨氏模量失配度,层错能变化及长程和/或短程有序的影响[30]。在FeCoNiTi高熵合金体系中,半径较大的Ti原子(表2)易于与其它元素键合[31]。同时,合金元素的原子尺寸错配度高使FeCoNiTi高熵合金的固溶强化效应加强[2,32]。此外,Fe,Ti间杨氏模量失配度高达81.9%(表2),进一步提高了固溶强化效应。FeCoNiTi高熵合金的晶界强化来自其双相结构。与传统的晶界相比,异相界面(图4c中FCC/Laves)需要更高的应力才能实现应变传递[22]。此外,具有平行和三角形形态特征的同相(FCC/FCC和Laves/Laves)界面也提供了强化作用。对于平行界面,位错在具有超细尺寸的魏氏体板条间的滑移距离较小,而在平行魏氏体板条方向有较大的滑移程(图3c)。同时,板条间形成的三角形界面在结构上是稳定的(图3d)。因此,滑移位错容易限定在平行界面和三角界面内,有助于FeCoNiTi高熵合金的强化。

FeCoNiTi高熵合金韧化行为的原因是:位错滑移及形变孪晶提供FCC相的塑性应变,Laves相的变形机制则由位错滑移主导(图7,8)。由于多滑移及形变孪晶的激活,FCC相可作为“软”相提供塑性。此外,韧化行为也归因于由魏氏体板条(FCC相)和层状结构(Laves相)组成的双相组织。Laves相的位错滑移系相当有限,因此层状结构(Laves相硬相)比魏氏层状结构(FCC相,软相)具有更大的内在变形抗力。当FeCoNiTi高熵合金承受外加机械载荷时,硬Laves相和软FCC相共存而形成协同变形,使其产生延性。

4 结论

(1) FeCoNiTi高熵合金的铸态组织呈枝晶形态,在均匀化处理过程中枝晶生长并合并成粗晶组织,形成了层状结构(Laves相)和魏氏体板条(FCC相)。

(2) FeCoNiTi高熵合金的双相组织是克服强韧性失衡的关键因素(2.08 GPa抗压强度和超过20%的压缩率)。高强度源于硬Laves相(层状结构)的强化,而软FCC相(魏氏体板条)的位错滑移和变形孪晶使其具有延展性。

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