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金属顶刊双语导读丨Acta Mater. Vol.206，1 Mar. 2021（上）

2021-06-03 来源：GS_Metals

 

本期包含金属材料领域论文13篇，涵盖了增材制造、马氏体、高温合金、复合材料等，国内科研单位包括南京理工大学、重庆大学、上海交通大学等（通讯作者单位）。

 

Vol. 206 目录

1. Examining material constitutive response under dynamic compression and large plastic strains using in situ imaging of hole closure

利用孔洞闭合原位成像技术检测材料在大塑性应变动态压缩下的本构响应

 

2. Initiation of fatigue damage in ultrafine grained metal films

超细晶金属薄膜中疲劳损伤的萌生

 

3. Microstructure formation and mechanical properties of ODS steels built by laser additive manufacturing of nanoparticle coated iron-chromium powders

使用纳米颗粒包覆Fe-Cr粉末和激光增材制造技术制备ODS钢的组织及力学性能研究

 

4. Growth of faceted, monolayer-coated nanovoids in aluminium

铝中多面体单层涂覆纳米孔洞的长大研究

 

5. Nucleation and growth of gas bubbles in AlSi8Mg4 foam investigated by X-ray tomoscopy

AlSi8Mg4泡沫材料中气泡形核长大的X射线断层扫描研究

 

6. Grain size effect on tensile properties and slip systems of pure magnesium

纯镁中晶粒尺寸对拉伸性能和滑移体系的影响

 

7. The mechanism of dynamic strain aging for type A serrations in tensile curves of a medium-Mn steel

中锰钢A型锯齿形拉伸曲线的动态应变时效机理研究

 

8. Effect of Alloying Elements on the High-Temperature Tempering of Fe-0.3N Martensite

合金元素对Fe-0.3N马氏体高温回火的影响

 

9. Slip-twinning interdependent activation across phase boundaries: An in-situ investigation of a Ti-Al-V-Fe (α+β) alloy

α+β双相Ti-Al-V-Fe合金中滑移-孪生相互激活的原位研究

 

10. Segregation and precipitation stabilizing an ultrafine lamellar-structured Al-0.3%Cu alloy

偏聚和析出对Al-0.3%Cu超细层状组织的稳定性影响研究

 

11. Ultrahigh tribocorrosion resistance of metals enabled by nano-layering

金属多层纳米结构的耐磨损腐蚀性能研究

 

12. Thermal-solutal-fluid flow of channel segregation during directional solidification of single-crystal nickel-based superalloys

镍基单晶高温合金定向凝固过程中通道偏析的热流-溶质-流体流动

 

13. Strength and plasticity of lamellar vs. fibrous eutectic Mg-Al nanocomposites: An in-situ microcompression study

层状与纤维状共晶Mg-Al纳米复合材料强度和塑性的原位微柱压缩比较研究

 

 

ACTA

Vol. 206，1 Mar. 2021, 116584

1. Examining material constitutive response under dynamic compression and large plastic strains using in situ imaging of hole closure

利用孔洞闭合原位成像技术检测材料在大塑性应变动态压缩下的本构响应

 

Jonathan Lind✉, Matthew D. Nelms, Andrew K. Robinson, Mukul Kumar, Nathan R. Barton

J. Lind：lind9@llnl.gov

https://doi.org/10.1016/j.actamat.2020.116584

 

摘要

为了了解材料在动态加载下的性能，需要研究应变速率以及材料初始状态对动态响应的影响。研究者通往往基于形状变化来推断材料在高应变率(>103/s)下的流变强度。考虑到应力和应变的非均质性，通过模拟的比较，可以更好地从实验观测结果推断出流动强度。我们介绍了一种新的平板冲击实验测试方法，该方法采用原位X射线成像技术来观察圆孔在可控幅度和持续时间的压力脉冲下的闭合情况。我们采用多帧成像技术测量圆孔闭合情况随时间的变化，从而获取材料在高应变率下塑性响应数据。我们将实验结果与PTW（Preston-Tonks-Wallace）数值模拟和MTS（Mechanical Threshold Stress）流变强度模型的预测结果进行了比较。定量分析结果提供了高速率硬化行为的MTS模型参数，这些参数难以通过准静态实验获得。

向上滑动阅览英文摘要

For understanding material performance under dynamic loading, there is significant interest in the strain rate dependence of material response and in the degree to which high-rate response depends on initial material state. Experimental tests at high strain rates (>103/s) often use measurement of shape change to infer flow strength behavior. Given stress and strain heterogeneities, inferences about flow strength behavior from those observations are facilitated by comparisons with advanced simulations. A new plate impact-based experimental test is described, consisting of in situ X-ray imaging to observe the closure of a cylindrical hole during the passage of a pressure pulse of controlled amplitude and duration. With the goal of providing unique data regarding plastic response at high strain rates, the closure of the hole is measured through time using multi-frame imaging. A first set of experiments on copper examines the role of starting microstructure on material flow behavior. The experimental observations are compared with predictions from direct numerical simulations using the Preston-Tonks-Wallace (PTW) and the Mechanical Threshold Stress (MTS) flow strength models. The quantitative utility of the overall approach is demonstrated in that the results provide information about MTS model parameters associated with high-rate hardening behavior, with the parameters having been unconstrained by quasi-static experimental data.

 

 

ACTA

Vol. 206，1 Mar. 2021, 116599

2. Initiation of fatigue damage in ultrafine grained metal films

超细晶金属薄膜中疲劳损伤的萌生

 

O. Glushko✉, D. Kiener

O. Glushko：oleksandr.glushko@unileoben.ac.at

https://doi.org/10.1016/j.actamat.2020.116599

 

摘要

本研究的目的深入理解局部组织特征（如晶粒尺寸、晶粒取向、晶界特征等）和整体特征（如织构、晶粒尺寸分布、孪晶界分数等）对薄膜材料疲劳损伤萌生的影响。我们对于聚合物支撑的超细晶金和铜薄膜进行了振幅1%的循环应变，从而在单一宏观样品中观测材料的局部塑性响应。我们对发生塑性响应区域的微观组织进行了详细的背散电子衍射表征和统计分析。从微观组织上看，损伤发生在大晶粒（>1µm）附近特定取向的共格孪晶界附近。当初始组织中不存在满足条件的大晶粒时，机械诱导的晶粒粗化将促进疲劳损伤的发生。如果初始组织中没有满足取向条件的共格孪晶界，则动态粗化后的局部晶粒尺寸是控制塑性滑移集中的唯一参数。从宏观尺度上看，影响疲劳损伤萌生的组织参数主要是孪晶界比例、织构和晶粒尺寸分布的宽度。基于以上结果，我们对提高薄膜疲劳寿命的策略进行了讨论。

向上滑动阅览英文摘要

The aim of the current research work is to understand how individual local microstructure features such as grain size, grain orientation, grain boundary characteristics, as well as the global parameters of the microstructure (texture, grain size distribution, twin boundary fraction) influence the process of fatigue damage initiation in thin films. Cyclic strain with an amplitude of 1% was applied to polymer-supported ultrafine grained gold and copper films allowing for observation of numerous independent localized plasticity events within a single macrosample. Detailed electron backscatter diffraction analysis of the microstructure in the vicinity of these plasticity events was performed to gain statistical information and elucidate robust correlations. On the local scale, the damage was initiated in large grains (>1 µm) in the vicinity of coherent twin boundaries specifically oriented with respect to the loading direction. When appropriate large grains were not present in the initial microstructure, mechanically induced grain coarsening preceded fatigue damage initiation. If the initial microstructure did not contain properly oriented coherent twin boundaries, then the local grain size of dynamically coarsened grains was the sole parameter controlling plastic slip localization. On the global scale, the major parameters of the microstructure influencing the fatigue damage initiation process are the fraction of twin boundaries, texture, and the width of the grain size distribution. Based on the presented results a clear strategy for improving the fatigue life of thin films is proposed.

 

 

ACTA

Vol. 206，1 Mar. 2021, 116566

3. Microstructure formation and mechanical properties of ODS steels built by laser additive manufacturing of nanoparticle coated iron-chromium powders

使用纳米颗粒包覆Fe-Cr粉末和激光增材制造技术制备ODS钢的组织及力学性能研究

 

C. Doñate-Buendia, P. Kürnsteiner, F. Stern, M.B. Wilms, R. Streubel, I.M. Kusoglu, J. Tenkamp, E. Bruder, N. Pirch, S. Barcikowski, K. Durst, J.H. Schleifenbaum, F. Walther, B. Gault, B. Gökce✉

B. Gökce：bilal.goekce@uni-due.de

https://doi.org/10.1016/j.actamat.2020.116566

 

摘要

氧化物弥散强化(ODS)钢因其在高温或辐照条件下优异的机械性能而受到广泛关注。它们的组织与工艺密切相关，包括将纳米粒子加入基体钢粉，以及粉末的加工。对于ODS钢的增材制造而言，工艺的优化和控制仍是一个挑战。在此，我们通过介电控制吸附激光打印制备了含0.08 wt% Y2O3的PM2000 ODS钢，并对其组织、纳米粒子的演化和力学性能进行了表征和分析，研究了定向沉积(DED)和激光粉末熔化(LPBF)两种增材制造技术对ODS钢制备工艺的影响。与未添加Y2O3的DED和LPBF钢相比，ODS钢在600℃时的抗压强度分别提高了21%和29%。LPBF ODS钢的马氏硬度提高了9%，而DED ODS钢则没有明显变化。我们采用了背散电子衍射、扫描电子显微镜-X射线能谱和原子探针等方法，对DED和LPBF样品的围观组织和纳米粒子的组成、分布进行了研究。在600℃时，LPBF样品中Y-O纳米粒子的尺寸更小、分布更均匀，从而使得样品力学性能提高。通过限元方法模拟熔池，我们发现，LPBF的冷却速率比DED快约两个数量级，因此LPBF试样的粒子弥散程度和力学性能更佳。综上所述，本研究提出并验证了一种完全基于激光的ODS钢加工制备方法，并证明了该方法制备材料的组织和力学性能的优越性。

向上滑动阅览英文摘要

Oxide dispersion strengthened (ODS) steels are known for their enhanced mechanical performance at high temperatures or under radiation exposure. Their microstructure depends on the manufacturing process, from the nanoparticle addition to the base steel powder, to the processing of the nanoparticle enriched powder. The optimization and control of the processing steps still represent a challenge to establish a clear methodology for the additive manufacturing of ODS steels. Here, we evaluate the microstructure, nanoparticle evolution, and mechanical properties of ODS steels prepared by dielectrophoretic controlled adsorption of 0.08 wt% laser-synthesized yttrium oxide (Y2O3) on an iron-chromium ferritic steel powder (PM2000). The influence of the ODS steel fabrication technique is studied for two standard additive manufacturing techniques, directed energy deposition (DED) and laser powder bed fusion (LPBF). The compressive strength of the ODS steels at 600 °C is increased by 21% and 29% for the DED and LPBF samples, respectively, compared to the DED and LPBF steels manufactured without Y2O3 nanoparticle addition. The Martens hardness is enhanced by 9% for the LPBF ODS steel while no significant change is observed in the DED ODS steel. The microstructure and nanoparticle composition and distribution are evaluated by electron backscatter diffraction, scanning electron microscopy–energy-dispersive X-ray spectroscopy, and atom probe tomography, to compare the microstructural features of DED and LPBF manufactured parts. Smaller grain size and more homogeneous distribution with lower agglomeration of Y-O nanoparticles in the LPBF sample are found to be key factors for enhanced mechanical response at 600 °C. The enhanced mechanical properties of the LPBF-processed sample and the more homogeneous nanoparticle dispersion can be linked to results obtained by finite element methods simulations of the melt pool that show two orders of magnitude faster cooling rates for LPBF than for DED. Therefore, this work presents and validates a complete laser-based methodology for the preparation and processing of an ODS steel, proving the modification of the microstructure and enhancement of the high-temperature strength of the as-built parts.

 

 

ACTA

Vol. 206，1 Mar. 2021, 116594

4. Growth of faceted, monolayer-coated nanovoids in aluminium

铝中多面体单层涂覆纳米孔洞的长大研究

 

Xiaofen Tan✉, Matthew Weyland, Yu Chen, Timothy Williams, Philip N.H. Nakashima✉, Laure Bourgeois✉

X. Tan：xiaofen.tan1@monash.edu

P.N.H. Nakashima：philip.nakashima@monash.edu

L. Bourgeois：laure.bourgeois@monash.edu

https://doi.org/10.1016/j.actamat.2020.116594

 

摘要

孔洞虽然可能导致材料的结构或电磁性能失效，但同时在等离子体和光学方面具有重要的应用前景。了解孔洞机械、光电和热学性质的关键是准确表征其结构演化，特别是孔洞的表面。在此，我们报导了在两种铝合金中形成、且表面被单层锡涂覆的孔洞。在特定的热处理条件下，部分具有高纵横比的孔洞（“管状孔洞”）可以生长至几百纳米。通过原子尺度分辨率的扫描透射电子显微镜(STEM)和光谱技术，我们发现孔洞表面被单原子层锡壳连续覆盖，并且锡壳与铝基体具有相同的原子结构。管状孔洞通常附着在与Al基体具有特定取向关系的Sn粒子上，而等轴孔洞则不附着在这类Sn粒子上。管状孔洞的长径比强烈地受到Sn粒子与孔洞壳层Sn原子排列共格性的影响。这些管状孔洞可以看作是嵌入铝基体的单壁纳米管。它们具有重要的研究价值，因为它们比相同体积的等轴孔洞更容易引起机械或电磁故障。被涂层包覆的孔洞易制备、可调控、无污染，是未来局部表面等离子体共振(LSPRs)研究的理想材料。

向上滑动阅览英文摘要

Voids can cause structural and electrical failure in materials but also show promising properties for use in plasmonics and photonics. Key to understanding the mechanical, optoelectronic and thermal properties of voids is an accurate characterisation of their structure and evolution, in particular of their surfaces. Here we report the formation of voids, coated with a monolayer of tin, in two aluminium alloys. Amongst such voids, those with high aspect ratios (“tubular voids”) have been found to grow to hundreds of nanometres in length under certain heat treatment conditions. Using spectroscopy and atomic-resolution imaging in scanning transmission electron microscopy (STEM), we reveal that the voids are covered by a single-atomic-layer tin shell, which is continuous over the entire void surface and has the same atomic structure as the Al matrix. Tubular voids are invariably attached to Sn particles that have a specific orientation relationship with the Al matrix, whilst equiaxed voids are generally not attached to Sn particles exhibiting such an orientation relationship. The aspect ratios of tubular voids show a strong correlation with the coherence between the tin particle and the arrangement of the tin atoms in the void coating, along the growth directions of the tubular voids. These tubular voids could be considered as single-walled nanotubes that are embedded in the aluminium matrix and also as “anti-nanorods”. They are of great research interest because they are more likely to cause mechanical or electrical failure than equiaxed voids with the same volume. The coated voids are highly reproducible, controllable and free from contamination, and are therefore ideal for future studies of localized surface plasmon resonances (LSPRs).

 

 

ACTA

Vol. 206，1 Mar. 2021, 116583

5. Nucleation and growth of gas bubbles in AlSi8Mg4 foam investigated by X-ray tomoscopy

AlSi8Mg4泡沫材料中气泡形核长大的X射线断层扫描研究

 

Paul Hans Kamm✉, Tillmann Robert Neu, Francisco García-Moreno, John Banhart

P.H. Kamm：paul.kamm@helmholtz-berlin.de

https://doi.org/10.1016/j.actamat.2020.116583

 

摘要

泡沫金属的萌生和生长是一个复杂的动态过程，本质上具有三维空间和时间依赖性。时分辨断层扫描技术能够实时跟踪AlSi8Mg4合金在发泡过程中气泡的形核和生长，包括单个气泡的位置、大小和形状，时间步长为1s，空间分辨率为几µm。此外，我们还基于一系列三维图像成功识别出了气泡的组成，即Al-Mg相和TiH2颗粒。通过图像对气泡和气生相，以及它们之间的关系进行定量分析，我们把发泡的过程分为了两个阶段：（1）由吸附气体和组织中先发生熔融组分驱动的均一化；（2）合金熔化和TiH2粒子释放氢引起泡沫增长。研究表明，通过调控Al-Mg粉的性能，可以改善AlSi8Mg4泡沫金属的性能。

向上滑动阅览英文摘要

 

Initiation and growth of metal foam is a complex and dynamical process, which is intrinsically three-dimensional and time-dependent. Tomoscopy –or time-resolved tomography– allows us to follow the nucleation and growth of gas bubbles in AlSi8Mg4 alloy in real time during foaming. The location, size and shape of individual bubbles was determined in steps of 1 s with spatial resolutions of a few µm. Moreover, the constituents responsible for gas evolution, namely Al-Mg phases and TiH2 particles, were identified in the series of 3D images. Automated quantitative image analysis of bubbles and gas-generated phases including their spatial correlations allowed us to break down the foaming process into two distinct steps, a first homogenous one driven by adsorbed gases and first melting microstructural components and a second attributed to the melting of the alloy and subsequent foam growth driven by hydrogen released from TiH2 particles. The results of the study indicate that standard AlSi8Mg4 foam can be improved by tailoring the properties of the Al-Mg constituent powder.

 

 

ACTA

Vol. 206，1 Mar. 2021, 116604

6. Grain size effect on tensile properties and slip systems of pure magnesium

纯镁中晶粒尺寸对拉伸性能和滑移体系的影响

 

Kang Wei, Rong Hu, Dongdi Yin, Lirong Xiao, Song Pang, Yang Cao, Hao Zhou✉, Yonghao Zhao✉, Yuntian Zhu✉

H. Zhou：hzhou511@njust.edu.cn（南京理工大学）

Y. Zhao：yhzhao@njust.edu.cn（南京理工大学）

Y. Zhu：y.zhu@cityu.edu.hk（南京理工大学/香港城市大学）

https://doi.org/10.1016/j.actamat.2020.116604

 

摘要

晶粒细化可以显著提高金属材料的强度，但往往会降低材料塑性。我们发现，通过晶粒细化不仅可以提高镁合金的强度，而且由于激活了更多的滑移体系，同时也提高了延性。结果表明，由于基滑体系的限制，大晶粒尺寸(d=125 μm)纯Mg的塑性和均匀延伸率都较低(5.3%)。相比之下，细晶Mg (d=5.5 μm)的加工硬化能力、塑性以及均匀延伸率(18.3%)都得到了显著提高。双束条件的TEM分析表明，<c> 和 <c + a> 位错的激活是晶粒尺寸的减小后，合金性能提高的主要原因。此外，我们还发现，<c + a>位错不稳定，可能分解<c> 位错和<a>位错或I1层错。我们对纳米层错在提高镁合金强度和塑性方面的贡献及其形成机制进行了讨论。

向上滑动阅览英文摘要

Grain refinement can significantly enhance the strength of metallic materials, but usually at the sacrifice of ductility. Here we report that refinement of magnesium grains can not only improve its strength, but also its ductility, due to the activation of more slip systems. It is found that pure Mg with coarse grain size (d=125 μm) has a low ductility and uniform elongation (5.3%), due to the limited basal slip systems. In contrast, fine-grained Mg (d=5.5 μm) exhibits enhanced work hardening and ductility as well as uniform elongation (18.3%). Two beam condition TEM analysis revealed that the improved properties were due to the activation of non-basal dislocations, such as <c> and <c + a> dislocations with reducing the grain sizes. It is also found that the <c + a> dislocations are unstable and can dissociate into either <c> and <a> dislocations or I1 stacking faults. Contributions of nano stacking faults on strengthening and ductilization as well as their formation mechanism are rationalized and discussed.

 

 

ACTA

Vol. 206，1 Mar. 2021, 116613

7. The mechanism of dynamic strain aging for type A serrations in tensile curves of a medium-Mn steel

中锰钢A型锯齿形拉伸曲线的动态应变时效机理研究

 

Jae-Hoon Nam, Seon-Keun Oh, Myeong-heom Park, Young-Kook Lee✉

Y.-K. Lee：yklee@yonsei.ac.kr

https://doi.org/10.1016/j.actamat.2020.116613

 

摘要

本文旨在阐明动态应变时效(DSA)对Fe-5.15Mn-0.15C-0.37Si-0.0039N (wt%)中Mn钢锯齿形拉伸流变的影响机理。该试样为残留奥氏体(γR)、铁素体(α)和回火马氏体(α’T)三相。为此，我们在温度273 - 333K、初始应变率5 × 10−4 - 1 × 10−2 s−1的各种条件下对试样进行了拉伸。拉伸曲线显示，试样在Lüders带扩展后表现出A型锯齿状流变。锯齿与α和α’T均无关；它们并非由应变诱导马氏体相变引起的，而是由γR中的DSA引起。由于驻留时间和二次取向时间之间没有交叠，因此基于分位错和C-Mn配合物相互作用的短程扩散模型无法解释DSA。基于考虑长程扩散的位错阻滞模型，测量了锯齿形流变的γR临界应变 (ecγ) 。他们表现出正常的PLC行为，即ecγ值随着温度的增加和初始应变率的降低而降低。基于ecγ 测得的活化能与碳原子的位错管道扩散活化能接近。以上结果表明，中锰钢中的DSA可以用基于C原子的长程管道扩散的位错阻滞模型解释，而不能用基于C- Mn配合物的二次取向的短程扩散模型解释。

向上滑动阅览英文摘要

The objective of the present study is to clarify the mechanism of dynamic strain aging (DSA) causing serrations in tensile flow curves of Fe-5.15Mn-0.15C-0.37Si-0.0039N (wt%) medium-Mn steel specimens with triple phases of retained austenite (γR), ferrite (α) and tempered martensite (α'T). For the purpose, tensile tests were performed at various conditions of deformation temperature (Td = 273-333 K) and initial strain rate (έini = 5×10−4 - 1×10−2 s−1). The medium-Mn steel specimens revealed type A serrations after the propagation of the Lüders band in their tensile curves. The serrations were not related to both α and α'T; they were not caused by strain-induced martensitic transformation, but by DSA in γR. The DSA was not explained by the short-range diffusion model based on the interaction between partial dislocations and C-Mn complexes due to the absence of intersection between staying time and reorientation time. In a viewpoint of the dislocation arrest model involving long-range diffusion, critical strains of γR for serrations (ecγ) were measured. They showed the normal Portevine-Le Châtelier behavior that the ecγ value decreases with increasing Td and with decreasing έini. The activation energy measured using the ecγ values was similar to the activation energy for the dislocation pipe diffusion of C atoms. This result indicates that the DSA occurring in the present medium-Mn steel is explained by the dislocation arrest model involving the long-range pipe diffusion of C atoms, not by the short-range diffusion model involving the reorientation of C-Mn complexes.

 

 

ACTA

Vol. 206，1 Mar. 2021, 116612

8. Effect of Alloying Elements on the High-Temperature Tempering of Fe-0.3N Martensite

合金元素对Fe-0.3N马氏体高温回火的影响

 

Shao-Wen Young, Mitsutaka Sato✉, Kazuhiro Yamamitsu, Yusuke Shimada, Yongjie Zhang, Goro Miyamoto, Tadashi Furuhara

M. Sato：m-sato@imr.tohoku.ac.jp

https://doi.org/10.1016/j.actamat.2020.116612

 

摘要

我们对气相氮化+淬火制备得到的Fe-0.3mass%N-1mass%M (M: Cr, Mo, Mn, Si)马氏体在高温回火过程中的氮化物析出行为进行了研究。与Fe-N二元合金相比，Si的添加并没有在回火软化方面引起明显变化，Mn、Cr、Mo的添加减少了材料的回火软化，并且回火温度高于673K时，Cr、Mo合金发生了二次硬化。X射线衍射和TEM表征表明，773K回火过程中，存在氮化铁(γ′-Fe4N)和其他氮化物的析出。球差矫正STEM-HAADF表征表明，在Cr、Mo合金中，沿{001}α'平面形成了亚稳单层氮-合金元素团簇，并且这种团簇最终增厚形成为B1型MN沉淀。我们在含Mn合金中发现了B1型Mn氮化物，它可随厚度增加而转变为η-Mn3N2。3DAP分析证实，氮与合金元素的比值与STEM-HAADF所推导的结构一致。进一步分析表明，体系中还存在无法通过STEM-HAADF和3DAP明确表征的细小团簇。通过分析析出和位错强化对材料回火后硬度的贡献，我们推测，未检测到的Cr- N团簇同样有助于提高合金的硬化。

向上滑动阅览英文摘要

The precipitation behaviors of alloy nitrides during the high-temperature tempering of Fe-0.3mass%N-1mass%M (M: Cr, Mo, Mn, or Si) martensite obtained by gaseous nitriding and quenching was investigated. Resistance to temper softening was observed with the addition of Mn, Cr, and Mo and secondary hardening occurred in the Cr and Mo alloys at tempering temperature above 673K although Si addition did not result in clear change in temper softening in comparison to the Fe-N binary case. X-ray diffraction analysis and conventional TEM observation shows the precipitation of iron nitride (γ'-Fe4N) and alloy nitride during tempering at 773K. Cs-corrected STEM-HAADF observation revealed that metastable mono-layered nitrogen-alloying element clusters are formed along {001}α' plane and they are eventually thickened into B1-type MN precipitate in the Cr and Mo alloys. In the Mn alloy, B1-type Mn nitride was detected which presumably changes to η-Mn3N2 by thickening. 3DAP analysis confirmed the ratio of nitrogen and alloying element of the nitride corresponds to the structure deduced by STEM-HAADF. Clustering analysis of 'matrix' indicated that there are still finer clusters which could not be clearly visualized in STEM-HAADF and 3DAP. Hardness after tempering was examined by strengthening by precipitation and dislocations, suggesting that undetected Cr-N clusters should contribute to hardening in the Cr alloy.

 

 

ACTA

Vol. 206，1 Mar. 2021, 116520

9. Slip-twinning interdependent activation across phase boundaries: An in-situ investigation of a Ti-Al-V-Fe (α+β) alloy

α+β双相Ti-Al-V-Fe合金中滑移-孪生相互激活的原位研究

 

Shaolou Wei, Gaoming Zhu, Cemal Cem Tasan✉

C.C. Tasan：tasan@mit.edu

https://doi.org/10.1016/j.actamat.2020.116520

 

摘要

即使在单相合金中，组织塑性应变分布的演化也具有高度不均匀性。跨晶界/相界的滑移/孪晶迁移是引起这种非均匀性的重要因素之一。在这方面，跨晶界迁移的基本原理已经受到了广泛关注，而对相界的研究仍较少。我们认为(α+β)钛合金是研究这一现象的优秀材料，因为：（1）在相近的微观应变下，两相都可以表现出塑性变形;（2）位错滑移和机械孪晶的发生都可以松弛塑性应变。在本研究中，我们证实了一种包含β相中的位错滑移和α相中的{101-2}孪晶的形变传递单元。通过晶体学计算，我们发现可以使用Schmid因子结合Luster-Morris相容性，对滑动-孪晶迁移的发生倾向进行量化。我们采用了原位应变映射方法，证明了这种迁移有助于缓解应变集中，从而促进材料均匀变形。

向上滑动阅览英文摘要

Microstructural plastic strain distribution evolution is highly heterogeneous even in single-phase alloys. One of the important factors that govern this heterogeneity is slip/twinning transfer across grain/phase boundaries. In this regard, the fundamentals of transfer across grain boundaries have drawn significant attention in the literature, while the understanding of phase boundaries remains comparatively limited. (α+β) titanium alloys provide a profound platform to explore these phenomena, since: (i) both of the present phases can exhibit plastic deformation at similar microscopic strain levels; and (ii) both dislocation slip and mechanical twinning can be triggered to accommodate plastic strain. In the present work, we evidenced a deformation transfer unit involving dislocation slip in the β-phase and {101-2}-mechanical twin in the α-phase. We revealed by crystallographic calculations that the combination of Schmid factor and the Luster-Morris compatibility factor enables a rational quantification for the inception propensity of the slip-twinning transfer event. Our in-situ strain mapping approach verified that this sort of transfer activity can plausibly alleviate strain incompatibility/localization, demonstrating the potential to facilitate deformation homogeneity.

 

 

ACTA

Vol. 206，1 Mar. 2021, 116595

10. Segregation and precipitation stabilizing an ultrafine lamellar-structured Al-0.3%Cu alloy

偏聚和析出对Al-0.3%Cu超细层状组织的稳定性影响研究

 

Linfei Shuai, Tianlin Huang✉, Tianbo Yu✉, Guilin Wu, Niels Hansen, Xiaoxu Huang

T. Huang：huangtl@cqu.edu.cn（重庆大学）

T. Yu：tiyu@mek.dtu.dk

https://doi.org/10.1016/j.actamat.2020.116595

 

摘要

理解通过大应变变形制备的超细叠层合金在退火过程中的粗化机制和溶质原子的作用，对于调控其组织和力学性能至关重要。本研究中，我们采用冷轧方法（压下量98%）制备了界面间距为200 nm的Al-0.3%Cu合金层状结构。组织中的Cu偏聚在高角度层界。在100 ~ 175℃的退火过程中，细小的Al2Cu颗粒在片层边界处优先析出。我们通过测量退火样品的层间距，对合金的回复动力学进行了分析，发现回复过程中表观活化能从初期的77 kJ/mol增加末期的106 kJ/mol。通过透射电子显微镜下的原位观察，我们发现，粗化主要是由片层边界形成的Y形结的运动导致，运动受到位错、位错边界和粒子不同程度的钉扎影响。随着位错界面取向差的增大、Al2Cu颗粒的粗化以及相互连接的界面和颗粒的共同作用，这种局部钉扎逐渐增强。以上研究结果表明了合金元素在变形和退火过程中对精细层状组织稳定性的重要影响，为稳定超细层状结构的制备提供了指导。

向上滑动阅览英文摘要

Understanding the coarsening mechanisms and the role of solute atoms during recovery annealing of ultrafine lamellar-structured alloys produced by high strain deformation is crucial to tailor their microstructures and mechanical properties. In the present work, a lamellar-structured Al–0.3%Cu alloy with a boundary spacing of 200 nm was prepared by cold rolling to a von Mises strain of 4.5 (a thickness reduction of 98%), featuring Cu segregation to high angle lamellar boundaries. During recovery annealing in the temperature range of 100–175 °C, precipitation of fine Al2Cu particles occurred preferentially at lamellar boundaries. Recovery kinetics was analyzed based on measurements of lamellar boundary spacings in the annealed samples, showing an increase in the apparent activation energy from 77 kJ/mol at the beginning to 106 kJ/mol at the end of recovery. In situ observations of annealing in a transmission electron microscope revealed that the dominant coarsening process is the motion of Y-junctions formed by lamellar boundaries, which is subjected to various degrees of pinning from dislocations, dislocation boundaries and particles. Furthermore, it was found that this local pinning effect can be reinforced with the increase of misorientation angles of the attached dislocation boundaries, the coarsening of Al2Cu particles and the combined effect of interconnecting boundaries and particles. The results underpinned the importance of alloying elements in stabilizing finely spaced lamellar structures during deformation and annealing, providing guidelines for tailoring stable ultrafine structured alloys.

 

 

ACTA

Vol. 206，1 Mar. 2021, 116609

11. Ultrahigh tribocorrosion resistance of metals enabled by nano-layering

金属多层纳米结构的耐磨损腐蚀性能研究

 

Wenbo Wang, Kaiwen Wang, Zhengyu Zhang, Jia Chen, Tianyou Mou, F. Marc Michel, Hongliang Xin, Wenjun Cai✉

W. Cai：caiw@vt.edu

https://doi.org/10.1016/j.actamat.2020.116609

 

摘要

金属表面的磨损腐蚀是其在腐蚀环境中长期服役所需面临的挑战之一。在本研究中，我们发现，金属多层纳米薄膜结构（NMMs）由于具有大量界面和纳米尺度的化学作用，能够有效限制塑性变形，减少微电腐蚀和表面活性，从而表现出优异的抗磨损腐蚀性能。我们主要研究了Al/X (X = Ti、Mg、Cu)等间距多层纳米薄膜结构材料（单层厚度~3nm）在室温下、0.6 M NaCl水溶液中的磨损腐蚀行为。我们采用了微纳力学和电化学测量方法，结合先进的材料表征技术，研究了组分对材料变形和失效机制的影响。结果表明，在磨损腐蚀过程中，Al/Mg和Al/Cu NMMs主要发生材料的腐蚀，而Al/Ti NMM则由于表面持续钝化而发生严重的塑性变形。我们通过有限元(FE)模拟验证了所有NMMs的磨损腐蚀行为，结果表明磨损和腐蚀的协同作用加速了材料在层界面和磨损裂纹边缘的损耗。最后，我们通过密度泛函理论(DFT)计算，揭示了纳米材料耐蚀性的成因。结果表明，纳米层化提高了铝的表面功函数，相比于纯铝，Cl的吸附强度降低，因此铝的表面反应活性和点蚀敏感性降低。以上研究结果为极端环境下多层、多相金属材料的选择和设计提供了指导。

向上滑动阅览英文摘要

Tribocorrosion damage on metal surfaces imposes a great challenge to their reliable long-term performance in corrosive environment. In the present work, we showed that nanostructured metallic multilayers (NMMs) exhibited ultrahigh tribocorrosion resistance owing to abundant interfaces and nanoscale chemical modulation that effectively restricted plastic deformation, reduced micro-galvanic corrosion and surface reactivity. Specifically, the tribocorrosion behaviors of equal-spaced Al/X (X = Ti, Mg and Cu) NMMs with ~ 3 nm individual layer thickness were studied in 0.6 M NaCl aqueous solution under room temperature. Nanomechanical and electrochemical measurements were coupled with advanced material characterization tools to study the effects of constituting materials on the deformation and degradation mechanisms. It was found that while corrosion dominated in Al/Mg and Al/Cu NMMs, severe plastic deformation dominated in Al/Ti during tribocorrosion due to sustained surface passivity. A finite element (FE) based computational model was developed and validated to quantify the tribocorrosion behavior of all NMMs, which showed accelerated material loss at layer interfaces as well as wear track edge resulting from the synergistic effects of wear and corrosion. Finally, density functional theory (DFT) calculations were carried out to uncover the origin of corrosion resistance in NMM. It was found that via nanolayering, the surface work function of Al was increased while Cl adatoms adsorb less strongly than that on pure Al, thus reducing the surface reactivity and pitting susceptibility. The combined experimental and computational study provides a guideline for future material selection and design of multilayered and multi-phase metals for use under extreme environment.

 

 

ACTA

Vol. 206，1 Mar. 2021, 116620

12. Thermal-solutal-fluid flow of channel segregation during directional solidification of single-crystal nickel-based superalloys

镍基单晶高温合金定向凝固过程中通道偏析的热流-溶质-流体流动

 

Neng Ren, Jun Li, Chinnapat Panwisawas, Mingxu Xia, Hongbiao Dong, Jianguo Li✉

J. Li：li.jun@sjtu.edu.cn（上海交通大学）

https://doi.org/10.1016/j.actamat.2020.116620

 

摘要

通道偏析（即斑点现象）是模铸造单晶涡轮叶片最复杂的缺陷之一，严重限制了叶片的力学性能。斑点现象是由凝固过程中热流-固相-液相流的不稳定引起的。因此我们需要深入理解模铸过程中的流体流动、传热和物质迁移。本研究中，我们建立了一种三维欧拉两相模型，对CMSX-4镍基单晶高温合金定向凝固过程中的烟道效应和通道偏析演化进行研究。结果表明，通道仅分布在钢锭表面，模型预测的通道偏析形貌与实验观测到的斑点形貌一致。在忽略横向热流的情况下，瑞利数准则对通道偏析的预测有所偏差，因为在显著扰动下，并不是所有的烟囱都能发展为通道偏析。在糊状区，从水平方向到铸造方向的溶体对流扰动将导致已有烟道消失，从而加剧通道偏析。一旦形成稳定的通道偏析，热溶质对流引起的溶质富集会进一步促进偏析。通道偏析很难在棒材中心持续形成，而在沿铸造方向的侧壁附近更容易发生。以上研究表明，较弱的侧向热流可以抑制通道偏析的形成，从而有效减少单晶铸造过程中的斑点现象。

向上滑动阅览英文摘要

Channel segregation – known as freckle – is one of the most complex defects which severely limit mechanical properties of investment cast single-crystal turbine blades. The freckle phenomenon is induced by the thermal-solutal-fluid flow instability during solidification process; it is therefore important to gain better understanding of the fluid flow, heat transfer and species transport during the investment casting process. In this work, a three-dimensional Eulerian two-phase model is developed to investigate chimney behaviours and the evolution of channel segregation in the directional solidification of nickel-based single crystal superalloy CMSX-4. The results reveal that the channels are merely distributed on the surface of ingot backed up with targeted experiments, and the morphology of the predicted channel segregation is also consistent with the observed freckle chains. By ignoring lateral heat flux, deviation in the prediction of channel segregation using Rayleigh number criterion is anticipated, because not all the chimneys can be developed into channel segregation under the significant perturbation. In the mushy zone, the perturbation of the melt convection from the horizontal direction to the casting direction leads to the extinction of existing chimneys, thereby exacerbating channel segregation. Once the stable channel segregation is formed, it will be developed steadily under further solute enrichment caused by thermal-solutal convection. Channel segregations is difficult to develop continuously in the centre of the representative rod, while channels near the lateral walls are more likely to develop stable flow along the casting direction. It is suggested that the weaker lateral heat flux can suppress the formation of channel segregation, providing an effective process design criterion for the freckle mitigation during the single crystal casting.

 

 

ACTA

Vol. 206，1 Mar. 2021, 116624

13. Strength and plasticity of lamellar vs. fibrous eutectic Mg-Al nanocomposites: An in-situ microcompression study

层状与纤维状共晶Mg-Al纳米复合材料强度和塑性的原位微柱压缩比较研究

 

Soodabeh Azadehranjbar✉, Bingqiang Wei✉, Dongyue Xie✉, Kaisheng Ming✉, Jian Wang✉, Jeffrey E Shield✉

S. Azadehranjbar：sranjbar@huskers.unl.edu

B. Wei：bwei5@huskers.unl.edu 

D. Xie：dyxlux@gmail.com

K. Ming：ming@unl.edu 

J. Wang：jianwang@unl.edu

J.E. Shield：jshield@unl.edu

https://doi.org/10.1016/j.actamat.2021.116624

 

摘要

镁合金由于其低密度和高强重比，而在汽车和航空工业中具有很大的应用潜力。强度低和室温成形性差是镁合金的主要缺陷。两相纳米结构是改善镁合金力学性能的一种可能方案。根据工艺参数的不同，可以通过共晶转变形成纤维或片层形貌。我们通过原位SEM微柱压缩实验，研究了这两种不同形貌对材料力学响应的影响。与纤维形貌相比，片层形貌的强塑积更佳。且两者的强度都显著高于纯Mg，前者是纯Mg的5倍，后者是纯Mg的12倍。纤维状共晶以牺牲了部分塑性，获得了更高的强度。对变形微柱的HR/TEM分析表明，片层形貌塑性较高主要是由于以下两点：（1）α相和β相均有较强的位错活动，引起层片的协调变形；（2）α层对β层的切变不稳定性具有重要的制约作用。而在纤维形态中则没有观察到这两种影响，因此它们通常沿β相晶体的密排面发生解理失效。

向上滑动阅览英文摘要

Owing to their low density and high strength-to-weight ratio, Mg alloys are attractive for automotive and aerospace applications. However, the current use of magnesium in the industry is limited due to the low strength and poor formability at ambient temperatures. Two-phase nanostructured materials are a promising solution to improve the mechanical properties of Mg alloys. Depending on processing parameters, either fibrous or lamellar morphologies can be formed via the eutectic transformation. In this work, the mechanical behavior of these two different morphologies were examined by in-situ SEM microcompression tests. The lamellar morphology exhibited a superior combination of strength and plasticity with respect to the fibrous morphology, and both showed superior strength relative to pure Mg, up to five-fold in the former and 12-fold in the latter. However, the higher strength in the fibrous eutectic was obtained at the expense of a low plasticity. According to the HR/TEM analyses of the deformed micropillars, the relatively high plasticity of the lamellar morphology was attributed to the two reasons; on the one hand, high dislocation activity was observed in both α and β phases and resulted in plastic co-deformation of the layers. On the other hand, the α layers played a significant role in restricting the shear instabilities that initiated in the β layers. Such an effect was not observed with the fibrous morphologies, and thus, they failed by cleavage along the closest-packed planes in the β crystal.