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金属顶刊双语导读丨Acta Mater. Vol.212，15 Jun. 2021（下）

2021-08-08 来源：Goal Science

 

本期包含金属材料领域论文12篇，涵盖了高温合金、纳米晶、高熵合金等，国内科研单位包括上海交通大学、北京科技大学等（通讯作者单位）。

 

Vol. 212 目录

1. Intermittent nucleation and periodic growth of grains under thermo-solutal convection during directional solidification of Al-Cu alloy

Al-Cu合金定向凝固过程中对流条件下晶粒的间歇性形核和周期性长大

 

2. Kinetics of cyclically-induced mechanical twinning in γ-TiAl unveiled by a combination of acoustic emission, neutron diffraction and electron microscopy

γ-TiAl中循环应变诱导孪晶动力学的声射、中子衍射和电子显微研究

 

3. Measuring simulated hydrogen diffusion in symmetric tilt nickel grain boundaries and examining the relevance of the Borisov relationship for individual boundary diffusion

镍对称倾侧晶界中的氢模拟扩散及其与Borisov模型的联系

 

4. Mechanisms of Ti3Al precipitation in hcp α-Ti

密排六方α-Ti中的Ti3Al析出机理

 

5. Microstructure evolution under [110] creep in Ni-base superalloys

镍基高温合金[110]蠕变过程中的组织演变

 

6. Modeling solid solution strengthening in high entropy alloys using machine learning

高熵合金固溶强化的机器学习研究

 

7. Precipitation in reactor pressure vessel steels under ion and neutron irradiation: On the role of segregated network dislocations

离子和中子辐照条件下反应堆压力容器钢铁材料中析出、偏聚和位错网状的演化及相互作用

 

8. Revealing Nanoscale deformation mechanisms caused by shear-based material removal on individual grains of a Ni-based superalloy

镍基高温合金单一晶粒在剪切加工中的纳米尺度变形机制研究

 

9. Strength, plasticity, thermal stability and strain rate sensitivity of nanograined nickel with amorphous ceramic grain boundaries

非晶陶瓷晶界强化镍纳米晶材料的强度、塑性、热稳定性和应变率敏感性研究

 

10. Tuning the degree of chemical ordering in the solid solution of a complex concentrated alloy and its impact on mechanical properties

多主元合金中的化学有序调控及其对力学性能的影响

 

11. Unique crystallographic texture formation in Inconel 718 by laser powder bed fusion and its effect on mechanical anisotropy

激光粉末熔炼Inconel 718中的独特织构及其对机械性能各向异性的影响

 

12. Vapor phase dealloying kinetics of MnZn alloys

MnZn合金的气相脱合金动力学

 

 

ACTA

Vol. 212，15 Jun. 2021, 116861

1. Intermittent nucleation and periodic growth of grains under thermo-solutal convection during directional solidification of Al-Cu alloy

Al-Cu合金定向凝固过程中对流条件下晶粒的间歇性形核和周期性长大

 

Yang Tang, Yue Wu, Ya Zhang, Yongbing Dai, Qing Dong, Yanfeng Han, Guoliang Zhu, Jiao Zhang✉, Yanan Fu, Baode Sun✉

J. Zhang：zj119@sjtu.edu.cn（上海交通大学）

B. Sun：bdsun@sjtu.edu.cn（上海交通大学）

https://doi.org/10.1016/j.actamat.2021.116861

 

摘要

合金凝固过程的自然对流显著影响液相中的传热传质，从而影响晶粒的形核和长大。了解对流对铸坯凝固过程的影响是控制铸坯性能的关键。本研究中，我们采用同步辐射X射线技术对Al-15Cu(wt.%)在不同温度梯度下的定向凝固过程进行了原位观察。我们通过图像处理技术可以得到了溶质在视场下的分布和固体的3D微观结构，从而确定渗透率和瑞利数随时间的变化。随后，我们定量研究了溶体流动与组织间的相互作用。结果表明，溶质元素周期性地从熔融区排出，成分过冷的震荡引起了晶粒的间歇性形核和周期性长大，进而引起了溶质渗透率和瑞利数的周期性振荡。此外，在溶质流和对流作用的共同影响下，溶质浓度和形核数的振荡幅度一般呈正弦变化。

向上滑动阅览英文摘要

The presence of natural convection during solidification of alloys significantly influences the heat and mass transfer processes in the liquid phase, and thus affecting the nucleation and growth behaviors of grains. It is crucial to understand the impacts of thermo-solutal convection on the solidification process to control the final properties of casting ingots. In this study, the directional solidification of Al-15wt.%Cu alloy under different temperature gradients has been in-situ observed using synchrotron radiation X-ray radiography. The solute distribution in the field of view (FOV) and three dimensional solid microstructure are obtained by our proposed image processing technique, which aims to determine the permeability and solutal Rayleigh number in the mushy zone over time. Then the interplay between the thermo-solutal flow and microstructure is quantitatively studied. Results indicate the solute elements are periodically discharged out of and confined to the mushy zone owing to the solutal instability in the mushy zone, which results in the periodic oscillation of solute concentration. Therefore, the oscillatory constitutional undercooling gives rise to the intermittent nucleation and periodic growth of grains, which in turn cause the periodic oscillation of permeability and the associated solutal Rayleigh number, thereby in turn resulting in the oscillation of solute concentration. Moreover, owing to the superposed solute flow and convective flow, the oscillation amplitudes of solute concentration and nucleation number vary in a sinusoidal manner in general.

 

 

ACTA

Vol. 212，15 Jun. 2021, 116921

2. Kinetics of cyclically-induced mechanical twinning in γ-TiAl unveiled by a combination of acoustic emission, neutron diffraction and electron microscopy

γ-TiAl中循环应变诱导孪晶动力学的声射、中子衍射和电子显微研究

 

A. Vinogradov✉, M. Heczko, V. Mazánová, M. Linderov, T. Kruml

A. Vinogradov：alexei.vinogradov@ntnu.no

https://doi.org/10.1016/j.actamat.2021.116921

 

摘要

我们对主要为γ相的TiAl合金的循环响应和组织演变进行了实时研究。我们采用TEM和SEM - ECCI/EBSD对循环变形过程中位错和机械孪晶的演化特征进行了定性描述。由于TEM只能提供局部和非原位信息，因此我们采用了原位中子衍射技术表征循环过程中的晶格应变分布。此外我们还测量了孪晶体积分数随加载循环次数的变化规律。我们通过以下手段对每个变形循环中控制应变硬化的过程进行了分析：(i)磁滞回线形状的统计分析, 从而表征与变形机制有关的应力分布,(ii) 原位声学数据的统计分析，从而获取变形机制的动力学信息。每种实验方法在描述和解释方面都自身的优点和局限性。多种手段的结合促进了对孪晶、位错滑移等主要变形机制的全面了解。结果表明，在不同的加载周期内，这些机制间的相互作用可以全面地解释TiAl合金的循环力学行为。这种相互作用决定了早期的疲劳损伤演化机制，并可能对室温下γ -TiAl合金的整体疲劳响应有重要影响。

向上滑动阅览英文摘要

The cyclic response and the microstructure evolution of the near γ-TiAl alloy are investigated by a blend of contemporary experimental techniques centred around in-situ acoustic emission (AE) measurements reflecting the cyclically-induced structural changes in the real-time scale. TEM and SEM – ECCI/EBSD examinations provided an adequate qualitative description of microstructural features associated with populations of dislocations and mechanical twins evolving concurrently in the course of cyclic deformation. Since the TEM offers only local and post-mortem information, the in-situ neutron diffraction technique scanning a large part of the gauge length was employed to characterise the lattice strain distributions with cycling. The volume fraction of twins as a function of loading cycles was obtained after loading or unloading half-cycles. The processes controlling the cyclic strain hardening during each deformation cycle were assessed by (i) the statistical analysis of the shape of the hysteresis loop aiming at the characterisation of distribution internal stress barriers for deformation mechanisms involved and (ii) the spectral and statistical analysis of AE data providing information on the kinetics of these mechanisms. Each of the used experimental methods brings its own set of advantages and limitations in terms of characterisation and interpretation. Their unique combination ensures a host of benefits that promote a comprehensive understanding of primary deformation mechanisms - deformation twinning, dislocation slip and detwinning. It is shown that the cyclic mechanical behaviour of the TiAl alloy can be comprehensively explained by the interplay between these mechanisms co-operating during each loading cycle. This interplay governs the behaviour of underlying mechanisms in the early stages of the fatigue damage evolution and likely determines the overall fatigue response of near γ -TiAl alloy at room temperature.

 

 

ACTA

Vol. 212，15 Jun. 2021, 116882

3. Measuring simulated hydrogen diffusion in symmetric tilt nickel grain boundaries and examining the relevance of the Borisov relationship for individual boundary diffusion

镍对称倾侧晶界中的氢模拟扩散及其与Borisov模型的联系

 

David E. Page, Kathryn F. Varela, Oliver K. Johnson, David T. Fullwood, Eric R. Homer✉

E.R. Homer：eric.homer@byu.edu

https://doi.org/10.1016/j.actamat.2021.116882

 

摘要

晶界是金属中重要的扩散途径。本文研究了氢在镍中扩散时不同晶界类型的影响。我们模拟了26种[1 0 0]对称倾斜晶界在几种温度下的变化，并提出了一种改进的均方位移法对晶界的扩散系数进行计算。我们分析了不同晶界的扩散率，晶界和体扩散速率随温度的变化有一交点。Borisov等人将晶界扩散速率与界面能进行了练习，我们对其模型进行了测试。尽管从未有研究采用Borisov关系研究溶质原子的间隙扩散，但当晶界扩散速率高于体扩散速率时，该关系式与模拟值吻合良好。由于晶界几何形状和激活状态，Borisov关系中的一些参数难以测量而一直采用假设值。我们的模拟数据为这些参数提供了物理估计，结果表明其中的一些需要重新考虑。此外，这项工作还表明，虽然尚需进一步验证，但Borisov关系可以合理地将氢的间隙扩散率与单个[1 0 0]对称倾斜镍晶界的界面能联系起来。

向上滑动阅览英文摘要

Grain boundaries are known to act as important diffusion pathways in metals. Here we examine how hydrogen diffusion in nickel grain boundaries is affected by different grain boundary types. We simulate 26 [1 0 0] symmetric tilt grain boundaries at several temperatures and develop a modified mean squared displacement method for isolating the grain boundary diffusivity from the bulk diffusivity. We analyze the diffusivity data for the different boundaries and find the grain boundary diffusivity to be higher than the bulk diffusivity up to a temperature where the two converge. We test a model developed by Borisov et al. (Phys. Met. Metallogr. 17, 1964, 80-84) that relates grain boundary diffusion to grain boundary interfacial energy. Despite the fact that the Borisov relationship has never been used to examine solute interstitial diffusion before, it fits the simulated diffusion data well for temperatures where the grain boundary diffusivity is higher than the bulk diffusivity. Some parameters in the Borisov relationship, related to the geometry of the grain boundary and its activated states, have always taken on assumed values because they are hard to measure or acquire. The fit of the simulated data provides estimates for these values that are physically realistic and provides evidence that the use of the traditionally assumed values should be reconsidered. This work also demonstrates that while there is a need for further validation, the Borisov relationship can reasonably relate solute interstitial diffusivity of hydrogen to the interfacial energy of individual [1 0 0] symmetric tilt nickel grain boundaries, whereas in the past it has been used to relate self diffusion and interfacial energy of a grain boundary network as a whole.

 

 

ACTA

Vol. 212，15 Jun. 2021, 116811

4. Mechanisms of Ti3Al precipitation in hcp α-Ti

密排六方α-Ti中的Ti3Al析出机理

 

Felicity F. Dear, Paraskevas Kontis, Baptiste Gault, Jan Ilavsky, David Rugg, David Dye✉

D. Dye：david.dye@imperial.ac.uk

https://doi.org/10.1016/j.actamat.2021.116811

 

摘要

我们采用透射电镜、原子探针和小角X射线散射相结合的方法对α-Ti-Al-X合金中Ti3Al α2有序畴的形核和长大进行了表征。我们将含有O、V或Mo的Ti-7Al (wt.%)模型合金在550℃时效最多120天，在中间时间点观察析出相。结果表明，合金中的析出长大至约30nm，体积分数根据成分不同达到6-10%不等。间隙O原子增加了α2相的平衡体积分数，而V、Mo对α2平衡体积分数的影响较小。添加任何一种溶质元素都可以增加形核密度，减小析出相尺寸和粗化速率，但Mo的效果最显著。粗化过程可以用LSW模型描述，这表明析出粗化主要由基体扩散控制，而非界面控制。固溶温度对形核密度有影响，这一结果支持了空位浓度影响α2形核的假说。所有溶质均增加成核数密度，这也与空位控制形核机制相符。

向上滑动阅览英文摘要

Nucleation and growth of Ti3Al α2 ordered domains in α-Ti–Al–X alloys were characterised using a combination of transmission electron microscopy, atom probe tomography and small angle X-ray scattering. Model alloys based on Ti–7Al (wt.%) and containing O, V and Mo were aged at 550◦C for times up to 120d and the resulting precipitate dispersions were observed at intermediate points. Precipitates grew to around 30nm in size, with a volume fraction of 6–10% depending on tertiary solutes. Interstitial O was found to increase the equilibrium volume fraction of α2, while V and Mo showed relatively little influence. Addition of any of the solutes in this study, but most prominently Mo, was found to increase nucleation density and decrease precipitate size and possibly coarsening rate. Coarsening can be described by the Lifshitz-Slyozov-Wagner model, suggesting a matrix diffusion-controlled coarsening mechanism (rather than control by interfacial coherency). Solutionising temperature was found to affect nucleation number density with an activation energy of Ef = 1.5 ± 0.4 eV, supporting the hypothesis that vacancy concentration affects α2 nucleation. The observation that all solutes increase nucleation number density is also consistent with a vacancy-controlled nucleation mechanism.

 

 

ACTA

Vol. 212，15 Jun. 2021, 116851

5. Microstructure evolution under [110] creep in Ni-base superalloys

镍基高温合金[110]蠕变过程中的组织演变

 

M. Cottura✉, B. Appolaire, A. Finel, Y. Le Bouar

M. Cottura：maeva.cottura@univ-lorraine.fr

https://doi.org/10.1016/j.actamat.2021.116851

 

摘要

我们采用二维和三维相场模拟研究了[110]方向蠕变加载过程中Ni基高温合金的微观组织演变。我们将相场模型和基于位错密度的晶体塑性模型进行了耦合。该模型中，每个滑移系统的位错密度遵循存储-恢复定律，并采用硬化矩阵来考虑位错之间的短程相互作用。研究表明，拉伸轴的微小取向差对组织演化有显著影响。完美对齐加载方向时，组织中形成棒状析出，而有微小偏差时，则形成筏状析出。机械载荷的精确方向不同，宏观蠕变行为也不同，这解释了实验结果的偏差。我们研究了非均匀和各向异性的弹塑和塑性驱动力的相对作用，发现塑性是筏状析出形成的主要驱动力。此外，我们的计算还表明，初始位错密度对析出形貌影响较小，但对蠕变曲线影响显著。

向上滑动阅览英文摘要

Microstructure evolutions in Ni-base superalloys are investigated during [110] creep loading using 3D and 2D phase field simulations. A recently developed phase field model coupled to a crystal plasticity model based on dislocation densities is employed. The model uses a storage-recovery law for the dislocation density of each glide system and a hardening matrix to account for the short-range interactions between dislocations. We show that small misorientations of the tensile axis strongly modify the evolution: rafting is observed for small deviations, as opposed to a microstructure made of rod-like precipitates when loading is performed along a perfectly aligned [110] direction. Depending on the precise direction of the mechanical load, different evolutions are obtained accompanied by strong modification of the macroscopic creep behavior, explaining the variety of results observed experimentally. The relative role of inhomogeneous and anisotropic elastic and plastic driving forces is also investigated, plasticity being the main driving force for rafting in the considered case. In addition, our calculations show that the initial dislocation density slightly modifies the precipitates morphology but the creep curve is significantly impacted.

 

 

 

ACTA

Vol. 212，15 Jun. 2021, 116917

6. Modeling solid solution strengthening in high entropy alloys using machine learning

高熵合金固溶强化的机器学习研究

 

Cheng Wen, Changxin Wang, Yan Zhang, Stoichko Antonov, Dezhen Xue, Turab Lookman, Yanjing Su✉

Y. Su：yjsu@ustb.edu.cn（北京科技大学）

https://doi.org/10.1016/j.actamat.2021.116917

 

摘要

固溶强化对单相高熵合金(HEAs)的力学性能至关重要。而由于高熵合金的成分范围极广，因此通过识别控制固溶强化的潜在因素来加速高熵合金的设计是一项具有重大意义的工作。本研究中，我们通过机器学习方法，包括特征构建和特征选择，证明了可以通过元素的电负性差导来表征高熵合金的固溶强化作用。与现有的物理模型相比，我们的模型在预测高熵合金的强度/硬度上表现出更加优越的性能。我们对模型在AlCoCrFeNi, CoCrFeNiMn, HfNbTaTiZr和MoNbTaWV这四种合金体系中的应用和预测进行了讨论。

向上滑动阅览英文摘要

Solid solution strengthening (SSS) influences the exceptional mechanical properties of single-phase high entropy alloys (HEAs). Thus, given the vast compositional space, identifying the underlying factors that control SSS to accelerate property-oriented design of HEAs is an outstanding challenge. In the present work, we demonstrate a relationship derived in terms of the electronegative difference of elements to characterize SSS for HEAs. We propose a model which shows superior performance in predicting solidsolution strength/hardness of HEAs compared to existing physics-based models. We discuss applications of our SSS model to HEA design and predict alloys with potentially high SSS in the four alloy systems AlCoCrFeNi, CoCrFeNiMn, HfNbTaTiZr and MoNbTaWV. Our findings are based on the use of machine learning (ML) methods involving feature construction and feature selection, which we employ to capture salient descriptors.

 

 

ACTA

Vol. 212，15 Jun. 2021, 116922

7. Precipitation in reactor pressure vessel steels under ion and neutron irradiation: On the role of segregated network dislocations

离子和中子辐照条件下反应堆压力容器钢铁材料中析出、偏聚和位错网状的演化及相互作用

 

G.R. Odette✉, N. Almirall, P.B. Wells, T. Yamamoto

G.R. Odette：odette@engineering.ucsb.edu

https://doi.org/10.1016/j.actamat.2021.116922

 

摘要

辐照后反应堆压力容器(RPV)中的高密度Mn-Ni-Si-Cu析出会引起硬化和脆化，从而限制反应堆使用寿命。本研究中，我们对辐照后低合金RPV钢中位错网状处的元素偏聚和析出进行了定量分析。分析主要基于热力学框架，该框架能够较好地描述辐照引起的非平衡扰动效应，如辐射诱导偏聚(RIS)。我们首次将Cu、Mn、Ni、Si的偏聚量化为了5 - 10nm的网状位错段，这些位错段通常被MnNiSi析出相(MNSPs)隔开;在含铜钢中，MNSPs常常附着形成富铜共析出(CRPs)。我们报道了16种RPV钢的原子探针(APT)数据，这些钢具有较宽的成分范围，分别在320℃和290℃受到中子和6.4 MeV Fe3+辐照。这项研究的关键在于，非极高的损伤剂量和辐照导致的扩散增强，有助于区分热力学平衡态和非平衡态效应导致。我们用一套完整的描述符来描述离子和中子辐照下的偏聚和析出，包括：a)位错处的溶质富集因子(EFs)及其随成分的变化; b)基体与位错析出相的各自特征。这些位错特征的形成可能是由于辐射诱导偏析，或热力学因素，或两者兼有。结合简单的模型，我们发现低铜钢中，偏聚促进了MNSP的形核。而在典型过饱和RPV钢中，析出相的快速生长由热力学驱动，直至达到可预测的平衡摩尔分数。

向上滑动阅览英文摘要

 

The ultrahigh density of Mn-Ni-Si-Cu precipitates that form in irradiated reactor pressure vessels (RPV) result in hardening and embrittlement, which may limit the service life of aging nuclear reactors. Here, we quantitatively analyze solute segregation to, and precipitation on, network dislocations in irradiated low alloy RPV steels. The analysis is based on a broad thermodynamic framework, which allows proper identification of possible non-equilibrium perturbative effects of irradiation, like radiation induced segregation (RIS). For the first time, we quantify the segregation of Cu, Mn, Ni and Si to ≈ 5–10 nm network dislocation segments, typically separated by a string-of-pearl type array of MnNiSi precipitates (MNSPs); the MNSPs are appended to Cu rich co-precipitates (CRPs) in steels bearing this element. Detailed atom probe tomography (APT) data are reported for 16 RPV steels, with a wide matrix of tailored compositions, irradiated by both neutrons and 6.4 MeV Fe3+ ions at 320 and 290℃, respectively. A key aspect of this study is that the very high displacement per atom (dpa) doses and radiation enhanced diffusion (RED) result in nearly full phase separation, allowing isolation of thermodynamic (equilibrium or non-equilibrium) effects. We characterize segregation and precipitates with a comprehensive set of descriptors under both ion and neutron irradiation, including: a) solute enrichment factors (EFs) at dislocations, as a function of alloy composition; and, b) matrix versus dislocation precipitates and their respective characteristics. Formation of these dislocation features can be due to RIS, or thermodynamic in origin, or both. Coupled with simple models, we show that the nucleation MNSP features in low Cu steels is enhanced by segregation. However, in typical supersaturated RPV steels, rapid growth of the precipitates is thermodynamically driven to a quantitatively predictable, nearly full phase separation mole fraction

.

 

 

ACTA

Vol. 212，15 Jun. 2021, 116929

8. Revealing Nanoscale deformation mechanisms caused by shear-based material removal on individual grains of a Ni-based superalloy

镍基高温合金单一晶粒在剪切加工中的纳米尺度变形机制研究

 

Dongdong Xu, Thomas E.J. Edwards, Zhirong Liao, Xavier Maeder, Rajaprakash Ramachandramoorthy, Manish Jain, Johann Michler, Dragos Axinte✉

D. Axinte：Dragos.axinte@nottingham.ac.uk

https://doi.org/10.1016/j.actamat.2021.116929

 

摘要

剪切去除工艺对工件表面质量和工件性能有重要影响。我们通过原位扫描电子显微镜(SEM)对多晶镍基高温合金在切削过程中的晶体流变和晶格旋转进行了研究。对单晶进行纳米切削时，会出现一个变形纳米层，它由只在切削平面内旋转的晶格组成的；随着晶粒剪切引起的纳米切屑增加，变形纳米层的深度增加。当切削多个晶粒时，大角度晶界处发生纳米再结晶，并伴随着沿切削方向的晶界(GB)弯曲，这一现象也显著影响了晶粒的变形行为。在纳米尺度阐明以上问题对于理解切削后工件表面的损伤形成至关重要。

向上滑动阅览英文摘要

Shear-based material removal processes significantly influence the quality of workpiece surface and implicitly the component functional performance. An in-situ SEM nano-cutting enabled the study of crystal flow and lattice rotation occurring below the cutting edge in a polycrystalline Nickel superalloy. When nano-cutting within single grains a deformed nanolayer appears that consists of a crystal lattice rotated exclusively within the cutting plane which is delimited from the bulk of the grain by high angle boundary (HAB); the depth of deformed nanolayer increases with the material pile-up (nano-chip) caused by the grain shearing. Upon nano-cutting multiple grains, nano-recrystallisation at the HAB occurs, accompanied by the bending of the grain boundary (GB) in the cutting direction, a phenomenon that also significantly influences the deformation behaviour of the grains cut after passing the GB. Clarifying these aspects at the nanoscale is crucial for understanding the formation of workpiece surface damage after material removal operations.

 

 

ACTA

Vol. 212，15 Jun. 2021, 116918

9. Strength, plasticity, thermal stability and strain rate sensitivity of nanograined nickel with amorphous ceramic grain boundaries

非晶陶瓷晶界强化镍纳米晶材料的强度、塑性、热稳定性和应变率敏感性研究

 

Bingqiang Wei, Wenqian Wu, Dongyue Xie, Michael Nastasi, Jian Wang✉

J. Wang：jianwang@unl.edu

https://doi.org/10.1016/j.actamat.2021.116918

 

摘要

纳米晶(NC)金属材料中的大量晶界使得材料具有极高的强度。但纳米晶高温下的组织热稳定性较低，导致强度显著降低。因此，需要保持组织在高温下的稳定。本研究中，我们通过75 at.%Ni和25 at.% SiOC共溅射，在晶粒尺寸13 nm的纳米晶Ni中形成了1 ~ 2nm厚的非晶SiOC晶界，即制备得到了具有核壳结构的非晶陶瓷增强金属(NiSiOC ACRMs)。我们对材料的原始态、400℃退火态和压缩变形后的显微组织进行了表征，证实核壳结构的热稳定性。我们采用SEM下的原位微柱压缩实验测量了材料在室温至400℃范围内的机械性能，应力-应变响应和应变率敏感性。这一非晶陶瓷晶界增强材料具有极高的强度（室温~2.5 GPa，400℃~1.6 GPa）、优异的塑性（均匀压缩应变大于35%，无剪切失稳）和良好的热稳定性。材料的应变速率敏感性高（室温~0.015, 400℃~0.042），激活体积小（约13b3），且无明显的应变硬化/软化行为，这表明晶粒中存在位错滑移。非晶陶瓷晶界能够有效阻碍和捕获位错，强化材料，并促进Ni纳米晶与非晶陶瓷晶界的塑性协同变形; 位错沿非晶界面堆积，有效抑制了纳米晶间局部剪切带的形成。

向上滑动阅览英文摘要

A large fraction of grain boundaries imparts high strength to nanocrystalline (NC) metals but causes the poor thermal stability of microstructures and a significant reduction of strength with increasing deformation temperature. Stabilizing the microstructure is thus desired. In this work, we self-patterned 1-2 nm thick amorphous ceramic SiOC as grain boundaries in NC Ni with grain size of 13 nm through co-sputtering 75 at.%-Ni and 25 at.%-SiOC, producing Ni-SiOC amorphous ceramic reinforced metals (NiSiOC ACRMs) with a core-shell structure. Microscopic characterizations of Ni-SiOC ACRMs before and after 400℃ annealing and after compression deformation confirmed the thermally and mechanically stable core-shell structure. Mechanical properties, such as stress-strain responses and strain rate sensitivity of Ni-SiOC ACRMs over a range of temperatures from room temperature (RT) to 400℃ were measured using in situ micropillar testing in a scanning electron microscope (SEM). We demonstrated that amorphous ceramic SiOC grain boundaries impart a high strength (2.5 GPa at RT and 1.6 GPa at 400℃), large compressive plasticity (uniform compression strain greater than 35% without shear instability) and thermal stability to Ni-SiOC ACRMs. High strain rate sensitivity (0.015 at RT to 0.042 at 400℃), small activation volume (about 13b3) and no obvious strain hardening/softening behavior suggest that plastic deformation is accommodated by dislocation slips in Ni grains. Amorphous ceramic grain boundaries act as strong barriers and sinks for impeding and trapping dislocations, strengthening the ACRMs and promoting plastic co-deformation between Ni nanograins and amorphous ceramic grain boundaries; the accumulated dislocations are smeared along the amorphous-crystal interfaces, preventing formation of localized shear bands across multiple nanograins.

 

 

ACTA

Vol. 212，15 Jun. 2021, 116938

10. Tuning the degree of chemical ordering in the solid solution of a complex concentrated alloy and its impact on mechanical properties

多主元合金中的化学有序调控及其对力学性能的影响

 

S. Dasari, A. Jagetia, A. Sharma, M.S.K.K.Y. Nartu, V. Soni, B. Gwalani, S. Gorsse, R. Banerjee✉

R. Banerjee：raj.banerjee@unt.edu

https://doi.org/10.1016/j.actamat.2021.116938

 

摘要

我们基于二元混合焓，在Co-Cr-Fe-Ni体系中成功发现了一种高熵合金，即等原子比CoFeNi合金。随后的实验证实，该合金确实是一种接近理想状态的面心立方(FCC)随机固溶体。我们基于相同的热力学分析，通过添加适量的Al和Ti，对随机CoFeNi合金的化学有序状态，包括短程有序和长程有序进行了设计，因为这些元素与Co、Fe、Ni有很强的有序倾向(负混合焓)。基于3d过渡族金属之间的混合焓，我们设计了7种合金。研究表明，化学有序状态对合金屈服强度有显著影响，在相同的晶粒尺寸下，CoFeNi合金的屈服强度为~181 MPa, 而Al0.3Ti0.2Co0.7FeNi1.7合金的屈服强度为~793 MPa。实验测得的候选高熵合金屈服强度与简单强化模型的预测值基本一致。

向上滑动阅览英文摘要

Using the binary enthalpies of mixing in a Co-Cr-Fe-Ni base alloy system, a high entropy alloy (HEA) or complex concentrated alloy (CCA), the equiatomic CoFeNi has been identified, which should form a random solid solution. Subsequent experimental validation established that this alloy is indeed a near-ideal, random face centered cubic (FCC) solid solution. The same thermodynamic basis has been employed to systematically engineer the degree of chemical ordering within the random CoFeNi alloy, from localized domains of short-range ordering (SRO), also referred to as clustered ordering, to well-defined long-range ordered (LRO) domains, by adding controlled amounts of Al and Ti, since these elements have a strong ordering tendency (negative enthalpy of mixing) with Co, Fe, and Ni. A series of seven alloys were designed in this study, based on enthalpies of mixing among 3d transition metals. This change in the degree of chemical ordering has a strong influence on the tensile yield strength of the alloy, for the same nominal grain size, ranging from ~181 MPa in case of CoFeNi to ~793 MPa in case of the Al0.3Ti0.2Co0.7FeNi1.7 CCA. These experimentally measured yield strengths of the candidate CCAs are in close agreement with predicted values afforded by simple strengthening models.

 

 

ACTA

Vol. 212，15 Jun. 2021, 116876

11. Unique crystallographic texture formation in Inconel 718 by laser powder bed fusion and its effect on mechanical anisotropy

激光粉末熔炼Inconel 718中的独特织构及其对机械性能各向异性的影响

 

Ozkan Gokcekaya, Takuya Ishimoto, Shinya Hibino, Jumpei Yasutomi, Takayuki Narushima, Takayoshi Nakano✉

T. Nakano：nakano@mat.eng.osaka-u.ac.jp

https://doi.org/10.1016/j.actamat.2021.116876

 

摘要

增材制造的工艺参数有很高的自由度，因此很够很好地对各向异性组织进行调控。本研究中，我们用双向激光扫描，制备了一种具有特殊织构的IN718合金，从而调控其力学性能。我们在IN718中实现了3中不同的织构：< 110 >方向平行于制备方向的类单晶组织SCM,具有特定取向的层状组织CLM和弱织构的多晶组织。组织表征和有限元模拟表明，SCM和CLM的织构演变主要受熔池形状和相应的热流方向控制。与铸态IN718相比，由于层间界面的作用，CLM试样具有更好的力学性能。通过改变加载方向来调整应力传递系数和施密特系数，可以对CLM构件的强度-延性平衡进行调控。综上所述，我们为提高结构材料的力学性能提出了一种有前景的新方法。

向上滑动阅览英文摘要

Additive manufacturing offers an exclusive way of anisotropic microstructure control with a high degree of freedom regarding variation in process parameters. This study demonstrates a unique texture formation in Inconel 718 (IN718) using a bidirectional laser scan in a laser powder bed fusion (LPBF) process for tailoring the mechanical properties. We developed three distinctive textures in IN718 using LPBF: a single-crystal-like microstructure (SCM) with a <110> orientation in the build direction (BD), crystallographic lamellar microstructure (CLM) with a <110>-oriented main layer and <100>-oriented sub-layer in the BD, and polycrystalline with a weak orientation. The microstructure observations and finite element simulations showed that the texture evolution of the SCM and CLM was dominated by the melt-pool shape and related heat-flow direction. The specimen with CLM exhibited a simultaneous improvement in strength and ductility owing to the stress-transfer coefficient between the <110>-oriented main and <100>-oriented sub-grains, showing superior mechanical properties compared to cast-IN718. This behavior is largely attributed to the presence of the boundary between the main and sub-layers (crystallographic grain boundary) lying parallel to the BD uniquely formed under the LPBF process. Furthermore, the strength–ductility balance of the part with the CLM can be controlled by changing the stress-transfer coefficient and the Schmidt factor through an alteration of the loading axis. Control of the crystallographic texture, including the CLM formation, is beneficial for tailoring and improving the mechanical performance of the structural materials, which can be a promising methodology.

 

 

ACTA

Vol. 212，15 Jun. 2021, 116916

12. Vapor phase dealloying kinetics of MnZn alloys

MnZn合金的气相脱合金动力学

 

Zhen Lu, Fan Zhang, Daixiu Wei, Jiuhui Han, Yanjie Xia, Jing Jiang, Mingwang Zhong, Akihiko Hirata, Kentaro Watanabe, Alain Karma✉, Jonah Erlebacher✉, Mingwei Chen✉

A. Karma：alainkarma@gmail.com

J. Erlebacher：jonah.erlebacher@jhu.edu

M. Chen：mwchen@jhu.edu

https://doi.org/10.1016/j.actamat.2021.116916

 

摘要

气相脱合金化(VPD)是一种环保的纳米多孔材料制备方法，它利用元素饱和蒸气压不同的特点选择性对合金中一种或多种组分进行升华。目前关于复杂结构中固-气相变速率控制因素和VPD动力学的研究较少。我们以Mn-Zn合金为例，系统研究了脱合金速度随温度和压力的变化关系，并建立了定量的动力学模型。研究发现，由于动力学与微观组织的相互作用，脱合金速度的变化规律在某一临界深度将发生线性到幂律的转变。这种转变将早期蒸发过程和孔道中的Zn蒸气扩散联系了起来，而孔道中前沿的Zn分压处于固气平衡状态。我们通过比较VPD和Zn升华的活化能，测定了整个VPD过程的能量分布。以上VPD动力学研究对VPD材料的设计和组织优化提供了有效指导。

向上滑动阅览英文摘要

Vapor phase dealloying (VPD) is an environmentally-friendly method for fabricating nanoporous materials by utilizing the saturated vapor pressure difference of elements to selectively drive sublimation of one or more components from an alloy. VPD kinetics has not been explored and rate-controlling factors of the solid-gas transformation within complex nanostructure remain unknown. Using manganese-zinc alloys as a prototype system, we systematically investigated the dependence of dealloying velocity on temperature and pressure and presented a model to quantitatively describe the dealloying kinetics. We found that the dealloying velocity exhibits a linear to power law transition at a critical dealloying depth, resulting from the interplay between the kinetic process of dealloying and dealloyed microstructure. This transition bridges ballistic evaporation at early time to Knudsen diffusion of Zn vapor in developed pore channels where the Zn partial pressure at the dealloying front reaches the local equilibrium between the solid and vapor phases. By comparing activation energies for VPD and bulk zinc sublimation, the entire energy landscape of VPD is measured. The fundamental understanding of VPD kinetics paves an effective way to design dealloyable precursor alloys and to optimize dealloyed microstructure of VPD materials for a wide range of applications.