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金属顶刊双语导读丨Acta Mater. Vol.202，1 Jan. 2021（下）

2021-02-24 来源：Goal Science

本期包含金属材料领域论文13篇，涵盖了低合金钢、镁合金、多元合金、形状记忆合金与高温合金等，国内科研单位包括西安交通大学、上海交通大学、国立台湾大学等（通讯作者单位）。

 

Vol. 202 目录

1. In Situ Micro-Pillar Compression to Examine Radiation-Induced Hardening Mechanisms of FeCrAl Alloys

FeCrAl合金辐照诱导硬化机制的原位微柱压缩实验研究

 

2. 3D arrangement of atomic polyhedra in tilt grain boundaries

倾侧晶界中原子多面体的三维排布

 

3. An unexpected role of atomic oxygen dopants in Au evolution from clusters to a layer

氧原子掺杂剂在金团簇-层演化中的作用

 

4. Atomic scale understanding of the defects process in concurrent recrystallization and precipitation of Sm-Co-Fe-Cu-Zr alloys

Sm-Co-Fe-Cu-Zr合金同时发生再结晶和析出过程时缺陷演化的原子尺度研究

 

5. Isothermal bainite transformation in low-alloy steels: Mechanism of transformation

低合金钢的等温贝氏体相变机制研究

 

6. Interphase boundary layer-dominated strain mechanisms in Cu+ implanted Zr-Nb nanoscale multilayers

经Cu+注入的Zr-Nb纳米多层结构中受中间界面层控制的应变机制研究

 

7. Dissecting functional degradation in NiTi shape memory alloys containing amorphous regions via atomistic simulations

含非晶区NiTi形状记忆合金功能退化的原子尺度模拟研究

 

8.  Fracture mechanism and toughness of a rolled magnesium alloy under dynamic loading

轧制镁合金在动态载荷下的韧性与断裂机理

 

9. Intermediate structural evolution preceding growing BCC crystal interface in deeply undercooled monatomic metallic liquids

高度过冷的单一金属液体中BCC晶体生长前沿的中间态结构演化

 

10. Coupled crystal plasticity finite element-phase field model with kinetics-controlled twinning mechanism for hexagonal metals

六方金属中动力学控制孪晶机制的有限元-相场耦合模型

 

11. Alloys-by-design: Application to new superalloys for additive manufacturing

利用增材制造方法设计制备新型高温合金

 

12. Recovery of cold-worked Al0.3CoCrFeNi complex concentrated alloy through twinning assisted B2 precipitation

B2析出诱导孪晶引起的冷加工Al0.3CoCrFeNi多组元合金回复过程研究

 

13. Dendritic needle network modeling of the Columnar-to-Equiaxed Transition. Part II: three dimensional formulation, implementation and comparison with experiments

柱状晶向等轴晶转变的枝状针形网络三维模型模拟与实验对比

 

 

ACTA

Vol. 202，1 Jan. 2021, P255-265

1. In Situ Micro-Pillar Compression to Examine Radiation-Induced Hardening Mechanisms of FeCrAl Alloys

FeCrAl合金辐照诱导硬化机制的原位微柱压缩实验研究

 

Yuchi Cui, Eda Aydogan, Jonathan G. Gigax, Yongqiang Wang, Amit Misra, Stuart A. Maloy, Nan Li✉

N. Li：nanli@lanl.gov

https://doi.org/10.1016/j.actamat.2020.10.047

 

摘要

我们研究了300℃下5MeV Fe2+离子辐照对FeCrAl C26M合金组织演变和形变行为的影响。结果表明，当损伤剂量从1 dpa增加到16 dpa时，位错环的密度增加了一个数量级，而位错环的尺寸则逐渐饱和。我们制备了直径600 nm、高1.3μm的微柱，并对<001>、<011>和<111>取向的晶粒进行了压缩。在未辐照和经辐照的合金中，初始滑移系统均为{112}<111>。辐照后，沿<001>和<011>方向的屈服强度相比<111>方向有明显增加。Orowan势垒模型的相关分析表明，屈服强度的增加主要是由于辐射产生的缺陷环具有滑移抗力。我们通过TEM对应力升高时辐照诱导位错的分布和Burgers矢量进行了表征。结果表明，局部切变失稳是由于大量½<111>位错滑出实验柱引起的。同时，滑移带附近形成的大量<100>位错导致了合金在的应变硬化。

向上滑动阅览英文摘要

The effects of 5 MeV Fe2+ ion irradiation at 300°C on the microstructure evolution and deformation behavior of a FeCrAl C26M alloy are presented. It has been found that dislocation loop density increases an order of magnitude from 1 dpa to 16 dpa irradiations, whereas, the dislocation loop size saturates with increasing damage. Micropillars, 600 nm in diameter and 1.3 μm in height, were fabricated and compressed inside grains with <001>, <011> and <111> crystallographic orientations, respectively. {112} <111> has been identified as the primary slip system in both unirradiated and irradiated alloys. The increase in yield stress after irradiation is observed with measurable variation along <001> and <011> vs. along <111>. By applying the Orowan dispersed barrier model, the increase of yield stress is found mainly due to the slip resistance of radiation generated defect loops. Detailed transmission electron microscopy (TEM) studies were performed to quantify the Burgers vector and the distribution of irradiation induced dislocations at elevated strains. It is revealed that localized shear instability is caused by avalanche slip events of ½<111> dislocations gliding out of tested pillars. Simultaneously, a large number of sessile/immobile <100> dislocations formed in the vicinity of slip band, leading to the hardening at elevated strains.

 

 

ACTA

Vol. 202，1 Jan. 2021, P266-276

2. 3D arrangement of atomic polyhedra in tilt grain boundaries

倾侧晶界中原子多面体的三维排布

 

Kazutoshi Inoue✉, Kazuaki Kawahara, Mitsuhiro Saito, Motoko Kotani, Yuichi Ikuhara✉

K. Inoue：kinoue@wpi-aimr.tohoku.ac.jp

Y. Ikuhara：ikuhara@sigma.t.utokyo.ac.jp

https://doi.org/10.1016/j.actamat.2020.10.017

 

摘要

多晶材料的宏观性能与其晶体结构中的缺陷密切相关。晶界的独特性质取决于其附近及纳米的空间结构，因此对于构成晶界的原子多面体的类型和结构的研究就至关重要，尤其是晶界原子排布的数学规律和结构-性能关系。在本研究中，我们对[001]、[110]和[111]对称倾侧晶界的三维结构进行了分析。我们对这些多面体结构进行了严格定义，以区别二维模型中的多边形排布。研究表明，晶界区域只能由特定类型的多面体单元构成，且这些多面体之间的差异不大。我们通过数值分析对晶界的三维原子排布进行了系统的定量描述。不仅如此，我们还发现晶界层级遵循修正后的Farey图中所呈现的有理数分布规律。我们将由不超过两种多面体单元构成的晶界定义为奇异晶界，而任何晶界均可以由组成奇异晶界的多面体单元构成。

向上滑动阅览英文摘要

Polycrystalline materials have been used throughout the recorded history, and their macroscopic properties strongly depend on the defects in their crystalline structures. Unique properties of the grain boundaries (GBs) should result from nearby nano-scale space, leading to the questions regarding the type of atomic polyhedra that pack the GB region as well as the universal set of structural units. It is essential to reveal the underlying mathematical framework for the polyhedral arrangement of GB structures and identify the origin of structure-property relationships in polycrystalline materials, which is a fundamental aspect but important for designing high-performance materials. Herein, 3D atomic structures of [001], [110], and [111] symmetrical tilt GBs are analyzed in the face-centered cubic (fcc) crystals, where the polyhedral units are rigorously defined in contrast to the polygonal arrangement within the 2D structural unit model. It is concluded that the GB region can only be packed by the bulk or GB-type polyhedral units with minor variations. In this study, the 3D arrangement of atomic polyhedra around the GBs is quantitatively determined and systematically described by numerical analysis. Moreover, the GB hierarchy directly follows the distribution of rational numbers that is represented by the modified Farey diagram, which represents the 3D atomic structure of the symmetrical tilt GBs in an fcc crystal. The definition of singular GB is proposed as the GB packed by at the most two types of polyhedral units, and any GB can be packed by the polyhedral units that form the singular GBs.

 

 

ACTA

Vol. 202，1 Jan. 2021, P277-289

3. An unexpected role of atomic oxygen dopants in Au evolution from clusters to a layer

氧原子掺杂剂在金团簇-层演化中的作用

 

Eunwook Jeong, Eun-Ae Choi✉, Yoshifumi Ikoma✉, Seung Min Yu, Jong-Seong Bae,Sang-Geul Lee, Seung Zeon Han, Gun-Hwan Lee, Jungheum Yun✉

E.-A. Choi：eunae.choi@kims.re.kr

Y. Ikoma：ikoma@zaiko.kyushuu.ac.jp

J. Yun：jungheum@kims.re.kr

https://doi.org/10.1016/j.actamat.2020.10.063

 

摘要

结构调控是实现金的化学、电学和光学性能调控的重要手段。然而，由于缺乏有效手段避免Au在气相沉积过程（或之后）的本征结构演化，因此设计金的纳米结构一直是一个难题。在此，我们提出了一种方法：利用氧化诱导Au的聚集和分层。由于O对纳米金几何结构的最外层具有强烈的干涉效应，因此金的团簇以及和氧高度浸润的表层的演化显著加快。通过这一调控方式，我们成功制备出了4纳米厚的外延Au层结构，它比Ag具有更高的光学透明度，体电阻率接近于8×10−8Ω，并对化学腐蚀和机械变形的具有极好的抗性。这一结果为解决透明金属电极在工作环境中容易发生损坏导致性能劣化的问题提供了一个明确的解决方案。

向上滑动阅览英文摘要

Structure engineering is essential for manipulating the chemical, electrical, and optical properties of Au. However, it is challenging to design nanoscopic structures because no effective method is available to deviate from the intrinsic evolution behavior during and after synthesis via vapor deposition. Here, we propose an approach that utilizes the oxidation-induced clustering and layering of Au due to the strong O interference at the outmost surfaces of nanoscopic Au geometries. This promotes the evolution of Au clusters and layers that are highly wetted on their oxide supports. A 4-nm-thick epitaxial Au layer eventually evolved from the proposed growth mode, simultaneously exhibiting higher optical transparency than Ag, a near-bulk resistivity of 8 × 10−8Ω, and extreme resilience to chemical corrosion and mechanical deformation. This result provides a definite solution to transparent metal electrodes that are highly vulnerable to degradation in ambient and working environments.

 

 

ACTA

Vol. 202，1 Jan. 2021, P290-301

4. Atomic scale understanding of the defects process in concurrent recrystallization and precipitation of Sm-Co-Fe-Cu-Zr alloys

Sm-Co-Fe-Cu-Zr合金同时发生再结晶和析出过程时缺陷演化的原子尺度研究

 

Xin Song, Tianyu Ma✉, Xianglong Zhou, Fan Ye, Tao Yuan, Jingdong Wang, Ming Yue, Feng Liu, Xiaobing Ren

T. Ma：matianyu@xjtu.edu.cn （西安交通大学）

https://doi.org/10.1016/j.actamat.2020.10.067

 

摘要

理解过饱和固溶体时效时同时发生的再结晶和析出过程中的缺陷演化，对于理解它们的相互作用机制和组织调控至关重要，但在原子尺度上的相关研究却少有报导。我们通过透射电子显微镜对过饱和六方Sm(Co, Fe, Cu, Zr)7.5合金中，由于层错、空位、间隙原子等缺陷形成/分解导致的再结晶、亚晶形成、析出过程进行了详细研究。研究表明，扩散控制的<a>型分位错滑移不仅导致了基体由六方Sm(Co, Fe, Cu, Zr)7 (1:7H) 和Sm2(Co, Fe, Cu, Zr)17 (2:17H)的混合状态转变为了贫Sm的斜方Sm2(Co, Fe, Cu, Zr)17 (2:17R) ，并且提供了连续的扩散通道，抑制了点缺陷形成富Sm六方 Sm(Co, Fe, Cu, Zr)5 (1:5H) 晶胞界面析出和富Zr斜方(Sm, Zr)(Co, Fe, Cu)3 (1:3R)片晶。这表明存在一种扩散控制的相变机制，可以通过2:17R’ 中间相的成分进行描述表征，而成分取决于不完全基面滑移和元素偏聚。再结晶晶胞和析出相长大的速度都与缺陷密度密切相关，时效早期阶段缺陷密度高，长大速度快；后期阶段缺陷密度低，长大速度慢。我们提出了一种基面滑移模型对缺陷的分解/形成、以及同时形成的连续原子扩散通道进行了解释。以上研究可以帮助我们加深对再结晶和析出相互作用的了解。

向上滑动阅览英文摘要

Identifying the defects process in concurrent recrystallization and precipitation during aging a supersaturated solid solution is essential for understanding their interaction mechanisms and for manipulating the microstructure, but was rarely done at the atomic scale. Herein, the concurrent recrystallization and precipitation in the supersaturated hexagonal Sm(Co, Fe, Cu, Zr)7.5 alloys were studied through detailed transmission electron microscopy investigations, where the recrystallization, growth of recrystallized subgrains (cells) and precipitates stem from the gradual formation and dissociation of defects, including basal stacking faults (SFs), vacancies and excess interstitial atoms. The diffusion-controlled glides of <a>-type partial dislocations associated with the SFs not only transform the matrix from the mixture of hexagonal Sm(Co, Fe, Cu, Zr)7 (1:7H) and Sm2(Co, Fe, Cu, Zr)17 (2:17H) to Sm-depleted rhombohedral Sm2(Co, Fe, Cu, Zr)17 (2:17R) cells but also provide continuous diffusion channels to reduce the point defects to form the Sm-enriched hexagonal Sm(Co, Fe, Cu, Zr)5 (1:5H) cell boundary precipitates and Zr-enriched rhombohedral (Sm, Zr)(Co, Fe, Cu)3 (1:3R) platelets. It indicates a diffusion-controlled displacive phase transformation mechanism, characterized by the composition-dependent 2:17R’ intermediate phase due to incomplete basal slip and incomplete solute partitioning. The growth velocities of both recrystallized cells and precipitates are closely related to the defects density, being faster due to the high defects density at early stage, and being slower due to the reduced defects density at later stage. A basal slip model is proposed to explain the formation and dissociation of defects along with the stacking period change and the simultaneous formation of continuous atomic diffusion channels. These new findings may yield a deep understanding of the interaction between recrystallization and precipitation.

 

 

ACTA

Vol. 202，1 Jan. 2021, P302-316

5. Isothermal bainite transformation in low-alloy steels: Mechanism of transformation

低合金钢的等温贝氏体相变机制研究

 

Ravi Ranjan✉, Shiv Brat Singh✉

R.Ranjan：ravi.ranjan5@tatasteel.com, ravi.ranjan.9007@gmail.com

S.B. Singh：sbs22@metal.iitkgp.ac.in

https://doi.org/10.1016/j.actamat.2020.10.048

 

摘要

我们研究了奥氏体碳浓度对贝氏体等温相变的影响。结果表明，当奥氏体碳浓度较低且相变温度高于Zener有序温度时，贝氏体中的碳含量较低；而母奥氏体中碳含量较高且相变温度低于Zener有序温度时，贝氏体中的碳含量较高。我们基于碳原子的Zener有序会导致具有较高碳溶解度的BCT铁素体形成的相关理论，对实验结果进行了合理解释。类似地，我们发现在前一种情况中，未转变奥氏体中的碳含量接近T0线，而在后一种情况下，则高于T0线。我们基于BCT铁素体和奥氏体的平衡理论对这种碳浓度相对于T0的偏离进行了解释。最后，我们对贝氏体和奥氏体中碳含量的计算进行了修正，以便更好地计算当相变温度低于Zener有序温度时贝氏体和奥氏体的相对体积分数。

向上滑动阅览英文摘要

Effect of carbon concentration of parent austenite on isothermal transformation to bainite has been studied. It has been shown that when the carbon concentration of parent austenite is low and the transformation temperature is higher than the Zener ordering temperature, the carbon content of bainitic ferrite is low. On the other hand, it is unusually high when parent austenite has higher carbon and the transformation temperature is less than the Zener ordering temperature. The results have been rationalised on the basis of Zener ordering of carbon atoms resulting in the formation of BCT ferrite with higher solubility of carbon. Similarly, the carbon content of untransformed austenite in the former case was found to closely follow the T0 curve line whereas it was higher than T0 in the latter case. A theoretical framework based on the equilibrium between BCT ferrite and austenite has been proposed to explain the shift of the T0 curve to higher carbon concentration. Finally, the revised limits of carbon concentration of bainitic ferrite and austenite have been suggested for the calculation of the relative fractions of these phases when transformation temperature is less than the Zener ordering temperature.

 

 

ACTA

Vol. 202，1 Jan. 2021, P317-330

6. Interphase boundary layer-dominated strain mechanisms in Cu+ implanted Zr-Nb nanoscale multilayers

经Cu+注入的Zr-Nb纳米多层结构中受中间界面层控制的应变机制研究

 

N. Daghbouj✉, M. Callisti✉, H.S. Sen✉, M. Karlik, J. Cech, M. Vronka, V. Havránek, J. Capek, P. Minárik, P. Bábor, T. Polcar

N. Daghbouj：Nabil.Daghbouj@fjfi.cvut.cz

M. Callisti：m.callisti@hotmail.it

H.S. Sen：senhusey@fel.cvut.cz

https://doi.org/10.1016/j.actamat.2020.10.072

 

摘要

我们在高、低两种不同通量下，对溅射沉积制备的具有不同单层厚度（27nm或96nm）的Zr/Nb纳米金属多层薄膜注入了Cu+，随后采用了多种表征手段结合第一性原理计算，对其进行了研究。研究表明，注入Cu+后，薄层样品的Nb层中出现了沿c轴的拉伸应变，而Zr层中出现压缩应变，而厚层样品在Nb层和Zr层中均出现压缩应变。应变在薄层样品中较高，且随辐照通量的增加而增大。我们提出了一种数学方法来描述辐射损伤后，金属多层膜结构中的变形机制。在该模型中，单层累积的应变由界面应变和内部应变组成。模型的半解析解预测，界面应变占主导地位，并在界面周围的一定区域内扩展。这一结论得到了第一性原理计算的支持。第一性原理计算表明，空位和间隙原子在界面附近和Zr一侧比在Nb一侧具有更高的迁移率，因此具有更高的复合率，从而导致界面Zr侧的应变比Nb侧的应变小。我们将模型预测结果和第一性原理结合，得到了不同类型缺陷在不同离子损伤区的密度和分布。

向上滑动阅览英文摘要

Sputter-deposited Zr/Nb nanoscale metallic multilayers with a periodicity of 27 (thin) and 96 nm (thick) were subjected to Cu+ implantation with low and high fluences and then studied using various experimental techniques in combination with DFT calculations. After Cu+ implantation, the thinner multilayer exhibited a tensile strain along c-axis in Nb layers and a compressive strain in Zr layers, while the thicker multilayer showed a compressive strain in both layers. The strain is higher in the thin multilayer and increases for higher fluences. We developed a mathematical method for the fundamental understanding of the deformation mechanisms in metallic multilayers subjected to radiation damage. In the model, the cumulative strain within a layer is described as the combination of two contributions coming from the interfacial region and the inner region of the layers. The semi-analytical model predicts that the interfacial strain is dominant and extends over a certain region around the interface. Predictions are well supported by ab-initio calculations which show that in the vicinity of the interface and in the Zr side, vacancies and interstitials (low energy barriers) exhibit high mobility compared to the Nb side, thus resulting in a high recombination rate. As a consequence, less strain occurs in the Zr side of the interface compared to the Nb side. The density and distribution of various types of defects along the ion profile (low and high damaged regions) are obtained by combining DFT results and the predictions of the model.

 

 

ACTA

Vol. 202, 1 Jan. 2021, P331-349

7. Dissecting functional degradation in NiTi shape memory alloys containing amorphous regions via atomistic simulations

含非晶区NiTi形状记忆合金功能退化的原子尺度模拟研究

 

Won-Seok Ko✉, Won Seok Choi✉, Guanglong Xu, Pyuck-Pa Choi, Yuji Ikeda, Blazej Grabowski

W.-S. Ko：wonsko@ulsan.ac.kr

P.-P. Choi：p.choi@kaist.ac.kr

https://doi.org/10.1016/j.actamat.2020.10.070

 

摘要

我们使用分子动力学模拟，对含非晶区的纳米NiTi形状记忆合金的性能劣化进行了详细研究。通过对相关原子过程的深入理解，我们对实验观测到的现象，即材料在循环载荷下的塑性变形积累和残余应变突然增加，进行了解释。研究表明，形状记忆合金微柱在循环压缩下的力学响应显著地受非晶晶界或表面的影响。在循环加载下超弹性退化的主要原因是塑性变形的累积和由非晶区、晶体区协同作用产生的残留马氏体。而由于非晶相的存在，增加了马氏体的稳定性，导致了循环载荷下应力平台和滞回的减小。我们基于上述的性能劣化机制，对已报导的恢复超弹性方法进行了验证，并提出了新的方法来阻止非晶和晶体区的协同作用，例如在小尺度上实现形状记忆合金功能的稳定运行。

向上滑动阅览英文摘要

 

Molecular dynamics simulations are performed to provide a detailed understanding of the functional degradation of nano-scaled NiTi shape memory alloys containing amorphous regions. The origin of the experimentally reported accumulation of plastic deformation and the anomalous sudden increase of the residual strain under cyclic mechanical loading are explained by detailed insights into the relevant atomistic processes. Our work reveals that the mechanical response of shape-memory-alloy pillars under cyclic compression is significantly influenced by the presence of an amorphous-like grain boundary or surface region. The main factor responsible for the observed degradation of superelasticity under cyclic loading is the accumulated plastic deformation and the resultant retained martensite originating from a synergetic contribution of the amorphous and crystalline shape-memory-alloy regions. We show that the reported sudden diminishment of the stress plateaus and of the hysteresis under cyclic loading is caused by the increased stability of the martensite phase due to the presence of the amorphous phase. Based on the identifified mechanism responsible for the degradation, we validate reported methods of recovering the superelasticity and propose a new method to prohibit the synergetic contribution of the amorphous and crystalline regions, such as to achieve a sustainable operation of shape memory alloys at small scale.

 

 

ACTA

Vol. 202, 1 Jan. 2021, P350-365

8. Fracture mechanism and toughness of a rolled magnesium alloy under dynamic loading

轧制镁合金在动态载荷下的韧性与断裂机理

 

Arjun Sreedhar S, Suraj Ravindran, Gyan Shankar, S. Suwas, R. Narasimhan✉

R. Narasimhan：narasi@iisc.ac.in

https://doi.org/10.1016/j.actamat.2020.10.059

 

摘要

我们使用了液压试验机和Hopkinson杆装置分别对轧态AZ31镁合金的疲劳预裂三点弯试样进行了静态和动态断裂试验，并采用原位光学成像结合数字分析对实验结果进行了解释。研究发现，试样在静态加载下的断裂机制为孪晶诱导准脆性断裂，而在动态加载下则转变为微孔洞长大聚集。且随着加载速率的增加，试样尖端附近的拉伸孪晶减少；而远端的孪晶密度和织构则显著增加。在高加载速率下，由于背景塑性区的能量耗散增加，使得材料的断裂韧性显著增强。

向上滑动阅览英文摘要

Static and dynamic fracture experiments are performed using fatigue pre-cracked three-point bend specimens of a rolled AZ31 Mg alloy on a servo-hydraulic universal testing machine and a Hopkinson bar setup, respectively. The results are interpreted using in-situ optical imaging along with digital image correlation analysis. Microstructural analysis reveals that the fracture mechanism changes from twin-induced quasi-brittle cracking for static loading to micro-void growth and coalescence under dynamic loading accompanied by decrease in tensile twinning near the tip with loading rate. By contrast, the density of twins near the far-edge of the ligament and associated texture change enhance strongly with loading rate. The fracture toughness increases dramatically at high loading rates which is attributed to enhanced work of separation and dissipation in the background plastic zone.

 

 

ACTA

Vol. 202, 1 Jan. 2021, P387-398

9. Intermediate structural evolution preceding growing BCC crystal interface in deeply undercooled monatomic metallic liquids

高度过冷的单一金属液体中BCC晶体生长前沿的中间态结构演化

 

Zhenzhen Yan, Howard Sheng, Evan Ma✉, Bin Xub, Jinfu Li, Lingti Kong✉

E. Ma：ema.matscieng@gmail.com

L.Kong：konglt@sjtu.edu.cn （上海交通大学）

https://doi.org/10.1016/j.actamat.2020.11.001

 

摘要

我们对高度过冷的单质金属液体凝固时，晶体/液体界面的结构演化进行了理论分析。具体来说，我们使用了分子动力学模拟了BCC晶体长大前沿哑铃状间隙原子对（DILPs）的演化过程。这种方法使我们能够详细研究DILPs在并入晶格前的分布、相互联系、能量、以及动力学状态。研究表明，在高度过冷条件下，DILP并入生长中的晶体需要大量的原子协同作用和重排，因此需要激活能垒。相比之下，对于FCC晶体的长大，这种中间态结构能以一维链的形式通过简单滑移并入晶格。以上过渡模态和活化能垒的差异，能够帮助我们从结构演化的角度，解释BCC和FCC金属在高度过冷液体中晶体生长的速度差异。

向上滑动阅览英文摘要

We analyze the structural evolution at the arriving crystal/liquid interface in deeply undercooled elemental metallic liquids. Specifically, we use molecular dynamics simulations to monitor the intermediate dumbbell-interstitial-like pairs (DILPs) preceding the growing BCC crystal. This new defect-mediated approach has enabled us to examine in detail the population and interconnection, as well as the energetics and dynamics, of the DILPs before they join the crystal lattice. Under large undercooling the transition of the DILP motifs into the expanding crystal is found to require cooperative and collective rearrangement and hence thermal activation with an appreciable energy barrier. In comparison, the intermediate structural motifs in FCC-forming cases are primarily in the form of 1D chains, which can be incorporated into the growing lattice via easy slide. These differences in the transitional motifs and associated activation energy barrier offer a perspective from structural evolution standpoint to explain the very different crystal growth speed for BCC and FCC metals in deeply undercooled liquids.

 

 

ACTA

Vol. 202, 1 Jan. 2021, P399-416

10. Coupled crystal plasticity finite element-phase field model with kinetics-controlled twinning mechanism for hexagonal metals

六方金属中动力学控制孪晶机制的有限元-相场耦合模型

 

Guisen Liu✉, Hanxuan Mo, Jian Wang, Yao Shen✉

G. Liu：liuguisen@sjtu.edu.cn（上海交通大学）

Y. Shen：yaoshen@sjtu.edu.cn（上海交通大学）

https://doi.org/10.1016/j.actamat.2020.11.002

 

摘要

六方金属借助位错和孪晶的演化发生塑性变形。变形孪晶导致与晶体取向有关的孪晶畴的形成。在原子尺度上，孪晶畴通过孪晶位错/断点(TDs)的形核和运动来实现生长，而在微观/宏观尺度上，可以通过孪晶界(TBs)的迁移来对此进行描述。在本研究中，我们通过在微观尺度上耦合具有各向异性孪晶界迁移率的孪晶模型，建立了孪晶界迁移动力学的晶体塑性有限元-相场(CPFE-PF)模型。我们通过晶体塑性有限元(CPFEM)求解了位错滑移和孪生引起的弹性场和塑性变形。随后采用相场(PF)方法对孪晶畴与基体进行空间上的区分，并对孪晶界的迁移进行跟踪。孪晶界的迁移受孪晶驱动力和各向异性的晶界迁移率共同控制，其中迁移率借由实验测得的孪晶应变速率估计，而驱动力由晶体塑性有限元计算得到的应变能和由有限体积方法计算得到的界面能变化组成。值得一提的是，相场模型采用了实验测得的孪晶界面能和临界梯度准则来限制孪晶界的宽度。我们的CPFE-PF模型能够很好地预测实验观测到的孪晶长大行为，并可被进一步用于研究六方金属中与孪晶相关的组织演化和力学行为。

向上滑动阅览英文摘要

Hexagonal metals plastically deform through evolution of dislocations and twins. Deformation twinning is unidirectional and results in twin domain associated with crystal reorientation. Growth of a twin domain is accomplished through nucleation and motion of twinning dislocations/ disconnections (TDs) at atomic scale, and described by migration of twin boundaries (TBs) at micro/macro-scales. Corresponding to kinetics-controlled migration mechanisms of twin boundaries, a coupled crystal plasticity finite element-phase field (CPFE-PF) model was developed through implementing microscale twinning model with anisotropic mobilities of twin boundaries. Crystal plasticity finite element model (CPFEM) is used to solve elastic fields and plastic deformation (carried by both dislocation slip and twinning). Phase field (PF) method is adopted to spatially distinguish twin domains from matrix and track the migration of TBs. Migration of TBs is controlled by both anisotropic mobility coefficients that are correlated to experimental measured twinning strain rate, and the twin driving force contributed by strain energy that is calculated from CPFEM, and change of interface energy including chemical energy and gradient energy that is calculated using finite volume method. It is worth mentioning that experimental measured interface energies of TBs and a critical gradient criterion are adopted in PF model to confine the width of TBs. Our CPFE-PF model exhibits the capability of predicting twin growth with experimental observed twin morphologies, and can be further developed to study twinning related microstructural evolution and mechanical behavior for hexagonal metals.

 

 

ACTA

Vol. 202, 1 Jan. 2021, P417-436

11. Alloys-by-design: Application to new superalloys for additive manufacturing

利用增材制造方法设计制备新型高温合金

 

Yuanbo T. Tang, Chinnapat Panwisawas, Joseph N. Ghoussoub, Yilun Gong, John W.G. Clark, André A.N. Németh, D. Graham McCartney, Roger C. Reed✉

R.C. Reed：roger.reed@eng.ox.ac.uk

https://doi.org/10.1016/j.actamat.2020.09.023

 

摘要

我们使用了计算方法，设计出了可使用增材制造方法制备的新型γ/γ′镍基高温合金。在此过程中，我们充分考虑到了凝固和固态相变引起的裂纹和缺陷。我们使用激光粉末选区熔化方法对材料进行了试制，并将其与传统的IN939和CM247LC合金进行了比较。我们对材料进行了组织表征、热差分析和高温拉伸，结果表明设计出的新型合金具有优异的可加工性和力学性能。此外，我们对合金的设计模拟提出了一些可供改进的建议。

向上滑动阅览英文摘要

New grades of γ/γ′ nickel-based superalloy for the additive manufacturing process are designed using computational approaches. Account is taken of the need to avoid defect formation via solidification and solid-state cracking. Processing trials are carried out using powder-based selective laser melting, comparing with the heritage alloys IN939 and CM247LC. Microstructural characterisation, calorimetry and hot tensile testing are used to assess the approach employed. The superior processability and mechanical behaviour of the new alloys are demonstrated. Suggestions are made for refinements to the modelling approach.

 

 

ACTA

Vol. 202, 1 Jan. 2021, P448-462

12. Recovery of cold-worked Al0.3CoCrFeNi complex concentrated alloy through twinning assisted B2 precipitation

B2析出诱导孪晶引起的冷加工Al0.3CoCrFeNi多组元合金回复过程研究

 

S. Dasari, A. Sarkar, A. Sharma✉, B. Gwalani, D. Choudhuri, V. Soni, S. Manda, I. Samajdar✉, R. Banerjee✉

A. Sharma：abhishek.sharma@unt.edu

I. Samajdar：indra@iitb.ac.in

R. Banerjee：raj.banerjee@unt.edu

https://doi.org/10.1016/j.actamat.2020.10.071

 

摘要

虽然对纯金属和简单合金退火过程中的回复再结晶理论研究已经较为完善，但在高熵合金或多组元合金中(HEA/CCAs)，对这一过程的系统研究却相当有限。本文研究了经冷加工的Al0.3CoCrFeNi合金在等温退火回复过程中，位错湮没、孪晶形成和析出相形成之间的复杂相互作用。冷加工后，合金中含有高密的形变孪晶；等温退火后 Σ3孪晶界的比例进一步增加，并成为B2有序相的非均匀形核位点。等温退火后的非均匀组织由为粗大的非再结晶FCC晶粒和均匀分布在晶界、变形带和孪晶处的B2析出相组成。拉伸屈服强度随退火时间的延长而增加，我们认为这是由于Σ3孪晶界增加和晶界处的B2相修饰共同导致的。在700°C长时间退火后，合金屈服强度约为1010MPa，延伸率约为15%，同时伴随应变硬化的大幅恢复。

向上滑动阅览英文摘要

While the theory of recovery and recrystallization processes during annealing of pure metals and simple alloys is relatively well charted, systematic investigation of these processes in high entropy alloys or complex concentrated alloys (HEA/CCAs) is rather limited. The present paper focuses on the complex interplay between traditional recovery via dislocation annihilation, formation of annealing twins, and precipitation processes during isothermal annealing of a cold-worked candidate Al0.3CoCrFeNi HEA/CCA. While the cold-worked alloy contained a large number density of deformation twins, subsequent isothermal annealing resulted in a further increase in the fraction of Σ3 twin boundaries, which in turn acted as heterogeneous nucleation sites for ordered B2 precipitates. The heterogeneous microstructure obtained after isothermal annealing consists of coarse non-recrystallized FCC grains with high lattice curvature, and uniform distribution of B2 precipitates at prior grain boundaries, deformation bands and twins. The tensile yield stress increased with annealing time and this trend was attributed to the coupled effect of increasing fraction of Σ3 twin boundaries, and ordered B2 precipitates decorating these defects. After long-term annealing at 700°C the alloy exhibits an excellent combination of tensile yield stress ∼1010MPa and ductility ∼15%, as well as substantial recovery of the strain hardenability.

 

 

ACTA

Vol. 202, 1 Jan. 2021, P463-477

13. Dendritic needle network modeling of the Columnar-to-Equiaxed Transition. Part II: three dimensional formulation, implementation and comparison with experiments

柱状晶向等轴晶转变的枝状针形网络三维模型模拟与实验对比

 

Chih-Hung Chen✉, Amirhossein Molavi Tabrizi, Pierre-Antoine Geslin, Alain Karma✉

C.-H. Chen：chchen@iam.ntu.edu.tw （国立台湾大学）

A. Karma：a.karma@northeastern.edu

https://doi.org/10.1016/j.actamat.2020.10.012

 

摘要

枝状针形网络(DNN)模型通过追踪枝晶网络层级结构中枝晶前沿的扩散控制长大，可以很好地将不同尺度上的相场模型和粗晶模型联系起来。特别是，DNN模型放宽了粗晶模型中，对枝晶生长动力学和晶粒结构的假设。在本文的第一部分，我们提出了DNN模型的二维形式，并将其应用到了柱状晶-等轴晶转变(CET)的研究，阐明了这些假设对CET预测的影响。为了克服二维模型固有的局限性，在本文的第二部分，我们介绍了DNN模型的三维形式及其在CET中的应用。在验证了三维模型的有效性后，我们对Al-7wt.% Si合金的凝固过程进行了模拟，并将其与在国际空间站上进行的凝固项目实验结果进行了比较。结果表明，现有的三维DNN模型能够在实验的时间和长度尺度上定量地CET的位置和类型，而不需要任何可调参数。

向上滑动阅览英文摘要

The dendritic needle network (DNN) model tracks the diffusion-controlled growth of branches in the hierarchically structured dendritic network, thereby bridging the well-separated scales traditionally simulated by phase-field and coarse-grained models. In particular, the DNN model relaxes the assumptions on the dendrite growth kinetics and grain structures commonly used in the coarse-grained models. In part I of this paper, we proposed a two-dimensional (2D) version of the DNN model and applied it to investigate the Columnar-to-Equiaxed Transition (CET) to clarify the influence of these assumptions on the prediction of the CET. In order to overcome the limitations inherent in a 2D model, part II presents here a fully three-dimensional (3D) version of the DNN model and its application to the CET. After validation of the 3D model, we perform simulations to study the solidification of Al-7 wt.% Si alloy and compare the results to the experimental measurements conducted on board of the International Space Station in the framework of the CET in SOLidification processing (CETSOL) project. The comparison shows that the present 3D DNN model is able to provide quantitative prediction of the position and the type of CET at experimental time and length-scales, without any adjustable parameters.