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

2021-08-08 来源：Goal Science

 

本期包含金属材料领域论文11篇，涵盖了奥氏体、孪晶、高熵合金等，国内科研单位包括深圳大学等（通讯作者单位）。

 

Vol. 212 目录

1. A novel 3D mixed-mode multigrain model with efficient implementation of solute drag applied to austenite-ferrite phase transformations in Fe-C-Mn alloys

Fe-C-Mn合金奥氏体-铁氧体相变过程中溶质拖曳的3D混合模型

 

2. Atomic structures of interfacial solute gateways to θ’ precipitates in Al-Cu alloys

Al-Cu合金中θ′相界面溶质通道的原子结构研究

 

3. Columnar grain-driven plasticity and cracking in nanotwinned FCC metals

FCC纳米孪晶柱状晶的塑性与开裂

 

4. Dynamic recrystallization of Silver nanocubes during high-velocity Impacts

银纳米立方体在高速冲击下的动态再结晶

 

5. Dynamic strain aging mechanisms in a metastable austenitic stainless steel

亚稳奥氏体不锈钢的动态应变时效机制研究

 

6. Effect of sulfur on the glass-forming ability, phase transformation, and thermal stability of Cu-Zr-Al bulk metallic glass

硫对Cu-Zr-Al块体金属玻璃形成能力、相变和热稳定性的影响

 

7. Free surface impact on radiation damage in pure nickel by in-situ self-ion irradiation: can it be avoided?

能否避免自由表面对纯镍原位自离子辐照损伤的影响？

 

8. Increased magnetocaloric response of FeMnNiGeSi high-entropy alloys

FeMnNiGeSi高熵合金的磁热响应研究

 

9. Influence of microstructure and atomic-scale chemistry on the direct reduction of iron ore with hydrogen at 700°C

铁矿石在700℃氢气还原过程中的微观结构和成分演化

 

10. In situ study of non-equilibrium solidification of CoCrFeNi high-entropy alloy and CrFeNi and CoCrNi ternary suballoys

CoCrFeNi、CrFeNi和CoCrNi合金非平衡凝固的原位研究

 

11. Intercritical annealing of cold-rolled ferrite-pearlite steel: Microstructure evolutions and phase transformation kinetics

冷轧珠光体-铁素体钢临界退火过程中的组织演变和相变动力学研究

 

 

ACTA

Vol. 212，15 Jun. 2021, 116897

1. A novel 3D mixed-mode multigrain model with efficient implementation of solute drag applied to austenite-ferrite phase transformations in Fe-C-Mn alloys

Fe-C-Mn合金奥氏体-铁氧体相变过程中溶质拖曳的3D混合模型

 

H. Fang✉, S. van der Zwaag, N.H. van Dijk

H. Fang：h.fang@tudelft.nl, hfang@mek.dtu.dk, haixingfang868@gmail.com

https://doi.org/10.1016/j.actamat.2021.116897

 

摘要

同时考虑形核和界面迁移的三维模型是研究低合金钢复杂组织的有效工具。本研究中，我们开发了一个能在任意热处理路线下跟踪扩散界面，从而模拟奥氏体-铁素体相变和铁素体-奥氏体相变的三维多晶混合模型。模型考虑了置换型元素的溶质拖曳效益，并且当材料发生从加热到冷却的转变时，相变的方向也能够自发地随之改变。我们给出了计算溶质拖曳能量耗散的解析解，并结合化学势的多元回归逼近，大大加快了计算速度。我们首先以Fe-0.1C-0.5Mn (wt.%)合金为例，在不同的连续冷却和等温条件进行了计算。模型能够很好地模拟由于相邻晶粒的相互作用而导致的单一晶粒相变动力学差异。随后我们应用该模型对一系列Fe-C-Mn合金在循环相变过程中的动力学进行了预测。与实验结果的比较很好地验证了该模型关于铁素体相变动力学随Mn含量变化的预测。模型的创新点在于能够高效计算溶质拖曳的能量耗散、预测晶粒组织状态、且需要拟合的参数少。模型代码已公开。

向上滑动阅览英文摘要

A computational 3D model that accounts for both nucleation and interface migration is a very useful tool to monitor and grasp the complexity of microstructure formation in low-alloyed steels. In the present study we have developed a 3D mixed-mode multigrain model for the austenite-ferrite and the austenite-ferrite-austenite formation capable of following diffusional phase transformations under arbitrary thermal routes. This new model incorporates the solute drag effect of a substitutional element (in this case Mn) and ensures an automatic change in transformation direction when changing from heating to cooling and vice-versa. An analytical solution for calculating the energy dissipation of solute drag together with multiple regression approximations for chemical potentials are proposed which significantly accelerate the computation. The modelling results are first benchmarked for an Fe-0.1C-0.5Mn (wt.%) alloy under different continuous cooling and isothermal holding conditions. The model revealed relatively large variations in transformation kinetics of individual grains as a result of interactions with neighboring grains. Then the model is applied to predict the transformation kinetics of a series of Fe-C-Mn alloys during cyclic partial phase transformations. The comparison with experimental dilatometer results nicely validates the predictions of this model regarding the change in overall transformation kinetics of the ferrite transformation as a function of the Mn content. New features of this model are its efficient algorithm to compute energy dissipation by solute drag, its capabilities of predicting the microstructural state for spatially resolved grains and the minimal fine tuning of modelling parameters. The code to implement this model is publicly available.

 

 

ACTA

Vol. 212，15 Jun. 2021, 116891

2. Atomic structures of interfacial solute gateways to θ’ precipitates in Al-Cu alloys

Al-Cu合金中θ′相界面溶质通道的原子结构研究

 

M.F. Chisholm✉, D. Shin, G. Duscher, M.P. Oxley, L.F. Allard, J.D. Poplawsky, A. Shyam

M.F. Chisholm：chisholmmf@ornl.gov

https://doi.org/10.1016/j.actamat.2021.116891

 

摘要

亚稳强化相在高温下的转变或溶解对于材料性能至关重要。我们利用畸变校正扫描透射电子显微镜和第一性原理计算，对Al-Cu体系中的典型θ析出相Al2Cu的高移动性半共格界面的原子结构进行了研究。研究表明，半共格{110}界面由两种在不同结构单元中排列的错配配位错列组成。位错是铝基体和强化相间几乎所有错配的产生原因。Cu在界面特定位置的位错核受压边缘偏聚。第一性原理计算从能量角度对Cu原子在半共格界面处的运动进行了解释。研究揭示了影响析出强化合金热稳定性的半共格界面的关键特征。

向上滑动阅览英文摘要

Many materials employed in critical structural applications depend upon metastable strengthening precipitates that transform or dissolve at elevated temperatures. Herein, aberration-corrected scanning transmission electron microscopy and first-principles calculations are used to accurately determine the atomic structure of the highly mobile, semi-coherent precipitate interfaces that control this process in the classic θ’ (Al2Cu) precipitate in the Al-Cu system. Semi-coherent {110} interfaces are found to be composed of an array of unexpected misfit dislocations that are arranged in two different structural units. Dislocations accommodate nearly all of the misfit between the Al matrix and strengthening phase. Cu is observed to segregate to the compressed edge of the dislocation cores at specific sites in this interface. First-principles calculations revealed the energetic landscape that facilitates these sites to become entry and exit gateways of Cu atoms in this semi-coherent interface. This investigation reveals critical features within semi-coherent interfaces that determine the thermal stability of precipitation-hardened alloys.

 

 

ACTA

Vol. 212，15 Jun. 2021, 116925

3. Columnar grain-driven plasticity and cracking in nanotwinned FCC metals

FCC纳米孪晶柱状晶的塑性与开裂

 

Qiongjiali Fanga, Frederic Sansoz✉

F. Sansoz：frederic.sansoz@uvm.edu

https://doi.org/10.1016/j.actamat.2021.116925

 

摘要

研究者通常是从位错角度对含有特定取向纳米孪晶(nt)的柱状晶强塑性机制进行研究，而很少从晶界(GB)变形的角度进行研究。我们采用了大尺度分子动力学模拟方法，研究了四种BCC纳米孪晶柱状晶(Cu、Ag、Al、Ni)中晶界应变调节对塑性变形的影响。结果表明，在平行于共格孪晶界(CTB)的拉伸变形中，金属中的位错机制相同，并且与小CTB间距下的晶界扭结发射和大CTB间距下的位错缠结有关。随着剪切模量的增加，柱状晶孪晶金属的CTB强化效果越来越明显，这是由于GB应力集中与孪晶尺寸、金属类型和应变速率有关。随着CTB间距的减小，nt-Cu、nt-Ag和nt-Al的流动应力呈线性增加，而在nt-Ni在6 nm临界CTB间距下达到最大强度极限。这一强度极限是由GB滑移引起的柱状GB开裂造成的。对于柱状晶组织，nt-Ag和nt-Al中的GB滑动相当，nt-Cu中稍低，nt-Ni中则非常显著。以上发现强调了GB变形机制对柱状晶nt金属塑性和断裂的影响，对于加深对FCC金属中CTB强化的理解也有重要意义。

向上滑动阅览英文摘要

The mechanisms of strengthening and plasticity in columnar-grained metals with preferentially oriented nano-sized twins have been examined traditionally by considering dislocation processes, but rarely from the perspective of grain boundary (GB) deformation. Here, the effects of GB strain accommodation on plastic deformation in four different columnar-grained nanocrystalline nanotwinned (nt) face-centeredcubic metals (Cu, Ag, Al, and Ni) were studied by large-scale molecular dynamics simulations. It is observed that in tensile deformation parallel to coherent twin boundaries (CTBs), the dislocation mechanisms in each metal are identical and associated with GB emissions of jog and threading dislocations at small and large CTB spacings, respectively. However, CTB strengthening effects are increasingly more pronounced in columnar-grained nt metals as their shear modulus increases, which is rationalized by the dependence of GB stress concentrations on twin size, metal type and strain rate. Also, while flow stresses in nt-Cu, nt-Ag, and nt-Al metals increase linearly with decreasing CTB spacing, a maximum strength limit is reached in nt-Ni below a critical CTB spacing of 6 nm. The strength limit in nt-Ni results from columnar GB cracking induced by prominent GB sliding. For columnar-grained microstructures, GB sliding is equivalent in nt-Ag and nt-Al and slightly lower in nt-Cu but markedly higher in nt-Ni. These findings underscore the importance of new GB deformation mechanisms on plasticity and fracture in columnargrained nt metals and enrich our understanding of CTB strengthening in fcc metals synthesized in the literature.

 

 

ACTA

Vol. 212，15 Jun. 2021, 116892

4. Dynamic recrystallization of Silver nanocubes during high-velocity Impacts

银纳米立方体在高速冲击下的动态再结晶

 

David Funes Rojas, Okan K. Orhan, Mauricio Ponga✉

M. Ponga：mponga@mech.ubc.ca

https://doi.org/10.1016/j.actamat.2021.116892

 

摘要

我们通过分子动力学结合第一性原理计算，研究了银(Ag)单晶纳米立方体在高速冲击下的组织演变、动态再结晶和冲击后的晶格结构。我们的研究表明，在冲击作用下，在某些取向上能够形成由不同尺寸晶粒组成的复杂结构。这些取向的选择对应于至少八个或更多滑移系统的同时激活和位错雪崩。位错相互作用，并能够产生大量塑性变形促进纳米立方中的再结晶。另一方面，对于不同时激活滑移系统的取向，则没有观察到动态再结晶。通过高温下的第一性原理模拟，我们发现剧烈的塑性变形可以诱发面心立方结构向4H密排六方相的相变，而4H密排六方相比2H密排六方相在热力学上更加稳定。这些结果与实验结果吻合较好。我们的系统数值实验揭示了促进动态再结晶的因素，并为在冲击过程中通过取向调控材料的组织结构提供了指导。

向上滑动阅览英文摘要

We study microstructural evolution of Silver (Ag) single-crystal nanocubes during high-velocity impacts, their dynamic recrystallization, and post-impact lattice structure using a combination of molecular dynamics and ab-initio simulations. Our study shows that, upon the impact, some preferential orientations can develop intricate, architected microstructures with grains of different sizes. These selected orientations correspond to the cases where at least eight or more slip systems are simultaneously activated, leading to an avalanche of dislocations. These dislocations interact and have the ability to produce severe plastic work, stimulating recrystallization in the nanocubes. On the other hand, dynamic recrystallization is not observed for the orientations with asynchronously activated slip systems besides large shock-wave pressures, plastic deformation, and large dislocation densities. Using thermalized ab-initio simulations, we find that the severe plastic deformation can trigger phase transformation of the initial face-centered cubic lattice structure to the 4H hexagonal closed-packed phase, which is thermodynamically more stable than the 2H hexagonal closed-packed phase. These results are in good agreement with experimental works. Our systematic numerical experiments shed light on the factors that promote dynamic recrystallization and provide a pathway to control the microstructure and atomic structure simultaneously by orienting nanocubes during the impact.

 

 

ACTA

Vol. 212，15 Jun. 2021, 116888

5. Dynamic strain aging mechanisms in a metastable austenitic stainless steel

亚稳奥氏体不锈钢的动态应变时效机制研究

 

Javad Mola✉, Guoqing Luan, Qiuliang Huang, Christiane Ullrich, Olena Volkova, Yuri Estrin

J. Mola：j.mola@hs-osnabrueck.de

https://doi.org/10.1016/j.actamat.2021.116888

 

摘要

我们采用单轴拉伸试验对Fe-13Cr-3.4Mn-0.47C亚稳不锈钢在20 ~ 500℃范围内动态应变时效(DSA)引起的不连续塑性流变进行了研究。我们在已有模型上进行了改进，对中温区的复杂不连续流变及其消失进行了解释。不同温度区间的DSA机制不同。200°C以下，DSA由滑移带内的变形诱导马氏体相变引起。这一过程中，马氏体/奥氏体界面处的位错不发生运动，且界面不断向邻近的奥氏体发射新的位错。碳从马氏体向马氏体/奥氏体界面的快速扩散被认为是连续塑性流变中的一种钉扎机制。200-300°C区间内变形曲线上出现锯齿，这与奥氏体中碳扩散引起的位错钉扎有关。尽管在350-450°C，碳扩散速率增加，但此时无锯齿现象，碳原子持续拖拽溶质元素。而在500°C时，由于发生铬、锰原子对位错的钉扎，因此锯齿现象重新出现。

向上滑动阅览英文摘要

Discontinuous plastic flow due to dynamic strain aging (DSA) in a Fe–13Cr–3.4Mn–0.47C metastable stainless steel was studied by uniaxial tensile tests in the temperature range from 20 °C to 500 °C. A complex picture of the discontinuous flow and its disappearance in an intermediate temperature interval was interpreted in terms of an existing model, which had to be modified. Different mechanisms of DSA were proposed for different temperature intervals. DSA at temperatures up to 200 °C was attributed to deformation-induced martensitic transformation within glide bands. Immobilization of dislocations at martensite/austenite boundaries and emission of fresh dislocations into the adjacent austenite was considered as a major process in this temperature regime. Rapid diffusion of carbon from martensite to the martensite/austenite boundaries was considered as an additional pinning mechanism contributing to discontinuous plastic flow. Serrations on the deformation curves at temperatures between 200 °C and 300 °C were associated with dislocation pinning due to carbon diffusion in austenite. This regime of DSA did not involve high diffusivity martensite. In spite of an increase in the diffusivity of carbon in the temperature range of 350-450 °C, a serration-free regime was observed there. The absence of intermittent dislocation pinning/unpinning events responsible for serrations implied continuous solute drag by carbon atoms according to the Cottrell mechanism. Serrations reappeared at 500 °C and were attributed to dislocation pinning by substitutional chromium and manganese atoms.

 

 

 

ACTA

Vol. 212，15 Jun. 2021, 116923

6. Effect of sulfur on the glass-forming ability, phase transformation, and thermal stability of Cu-Zr-Al bulk metallic glass

硫对Cu-Zr-Al块体金属玻璃形成能力、相变和热稳定性的影响

 

Hao-Ran Jiang, Jing-Yi Hu, Nico Neuber, Benedikt Bochtler, Bastian Adam, Sascha S. Riegler, Maximilian Frey, Lucas Ruschel, Wen-Fei Lu, Ai-Han Feng✉, Ralf Busch, Jun Shen✉

A.-H. Feng：aihanfeng@tongji.edu.cn （同济大学）

J. Shen：junshen@szu.edu.cn（深圳大学）

https://doi.org/10.1016/j.actamat.2021.116923

 

摘要

我们通过常规XRD、高能原位同步辐射XRD、SEM、热差分析、热力学分析等方法研究了少量添加硫对Cu47.5Zr45.1Al7.4块体金属玻璃(BMG)的玻璃形成能力(GFA)、相组成、热稳定性和力学性能的影响。结果表明，硫对Cu-Zr-Al合金的GFA和热稳定性同时具有正反两方面的影响。一方面，硫可以减缓流体动力学，抑制熔体铸造和玻璃加热过程中共晶相析出，从而有利于含硫合金的玻璃相形成和热稳定性。另一方面，硫的加入促进了富Al的τ3相的形成，对GFA和熔体稳定性具有显著的负面效应。这两个因素相互作用，使得Cu-Zr-Al合金中的最佳硫含量约为0.75at.%。与原合金相比，添加硫后材料具有更好的玻璃形成能力、更大的过冷液相区和优异的机械性能，是一种富有前景的工业结构材料。此外，我们根据实验结果，阐明了时间-温度-相变图随硫浓度的变化。

向上滑动阅览英文摘要

The effects of minor sulfur addition on the glass-forming ability (GFA), phase formation, thermal stability, and mechanical properties of the Cu47.5Zr45.1Al7.4 bulk metallic glass (BMG) were studied by conventional X-ray diffraction (XRD), in-situ high-energy synchrotron XRD, calorimetry, thermomechanical analysis, and scanning electron microscopy. Results show that sulfur has positive and negative effects on the GFA and thermal stability of Cu-Zr-Al alloys. On the one hand, sulfur can slow down the liquid dynamics, thus inhibiting the precipitation of eutectic phases during casting from the melt and heating from the as-cast glass, and hence favoring the glass formation and thermal stability of the sulfur-bearing alloys. On the other hand, the addition of sulfur promotes the formation of an Al-rich τ3 phase, which easily precipitates and is therefore catastrophic for the GFA and melt stability. The two factors compete with each other and ultimately lead to an optimal sulfur content of 0.75 at.% for the investigated Cu-Zr-Al alloys. Compared with the base alloy, this novel sulfur-containing BMG possesses improved GFA, enlarged supercooled liquid region, and comparable mechanical strength and toughness, making it a promising candidate for industrial applications as structural material. Furthermore, the schematics of the change in time–temperature–transformation diagrams with increasing sulfur concentration were proposed on the basis of experimental results.

 

 

ACTA

Vol. 212，15 Jun. 2021, 116874

7. Free surface impact on radiation damage in pure nickel by in-situ self-ion irradiation: can it be avoided?

能否避免自由表面对纯镍原位自离子辐照损伤的影响？

 

Kan Ma, Brigitte Décamps, Anna Fraczkiewicz, Thomas Jourdan, Frédéric Prima, Marie Loyer-Prost✉

M. Loyer-Prost：marie.loyer-prost@cea.fr

https://doi.org/10.1016/j.actamat.2021.116874

 

摘要

自由表面的表面效应是原位辐照损伤研究中的难点之一。因此，我们需要对表面效应进行详细研究，从而对已有实验结果进行验证并为未来实验提供指导。由于Ni中的自间隙原子具有较高的迁移率，因此我们选择以Ni为对象对表面效应进行研究。我们采用2MeV的Ni2+离子在400-700°C下对超高纯度Ni薄膜进行原位辐照。根据试样厚度对位错环的影响，对其进行了微观组织演化分析和详细表征。研究取得的成果包括：(i)厚度对组织演变和辐照效应影响显著，且存在一个与温度有关的临界厚度;(ii)利用空位浓度计算模型很好地预测辐照厚度;(iii)自由表面对位错环的Burgers矢量分布有影响;(iv)通过考虑无环区域随温度的变化确定了Ni中的空位迁移能;(v)我们首次在510°C观察到，间隙原子减少10%有利于Ni中空位环的生长。

向上滑动阅览英文摘要

A major issue of in-situ radiation damage studies is related to the influence of free surfaces. Free surfaces in thin foils are indeed strong sinks for radiation-induced defects. Nevertheless, in-situ irradiationis a powerful tool to study real-time microstructural evolution and obtain insight into dynamic mechanisms of radiation damage. Thus, a detailed evaluation of surface effects is essential to validate existing results and provide guideline for future comparative experiments. In this work, nickel is chosen as model material to conduct systematic studies on surface effects due to the high mobility of its selfinterstitials. Ultra-high purity Ni thin foils are in-situ irradiated by 2 MeV Ni2+ ions at high temperatures (400-700°C). Microstructural evolution analysis and detailed characterization of dislocation loops are performed in function of specimen thickness.

The present work shows: (i) a drastic influence of thickness on the microstructural evolution and irradiated microstructure with the existence of a critical thickness depending on temperature; (ii) a good prediction of an adequate irradiation thickness with a vacancy concentration calculation model; (iii) an impact of free surfaces on the fine distribution of loop Burgers vectors; (iv) a first determination of migration energy of vacancies in Ni considering the temperature dependence of the loop-depleted zones; (v) a production bias model showing that a loss of 10% interstitials favors the growth of vacancy loops observed for the first time in Ni at 510°C.

 

 

ACTA

Vol. 212，15 Jun. 2021, 116931

8. Increased magnetocaloric response of FeMnNiGeSi high-entropy alloys

FeMnNiGeSi高熵合金的磁热响应研究

 

Jia Yan Law✉, Álvaro Díaz-García, Luis M. Moreno-Ramírez, Victorino Franco✉

J.Y. Law：jylaw@us.es

V. Franco：vfranco@us.es

https://doi.org/10.1016/j.actamat.2021.116931

 

摘要

具有优异磁热性能的高熵合金(HEAs)可能成为一种优异的功能材料。高熵合金的成分范围很大，磁热高熵合金通常在二级相变时表现出明显的磁热响应。本研究中，我们通过一种性能导向的搜索方法，发现多种具有不同Ge/Si比的FeMnNiGeSi高熵合金具有磁性结构一级相变。合金的等温熵变最高可达13 J kg-1K-1 (2.5T条件下)，这是迄今为止报道的具有最大磁热效应的高熵合金。这一性能已能与许多传统的磁热材料体系相媲美。以上研究为具有优异力学性能的高熵合金功能材料设计提供了指导。

向上滑动阅览英文摘要

The search for high-entropy alloys (HEAs), a new class of materials, with high magnetocaloric performance can address the open question about their potential in functional applications. HEAs exist in a vast compositional space but magnetocaloric HEAs typically exhibit modest magnetocaloric response as they undergo second-order magnetic phase transitions. In this work, through a property-directed search approach, FeMnNiGeSi HEAs with varying Ge/Si ratio are found in the large HEA space to exhibit magnetostructural first-order phase transition. Isothermal entropy change as large as 13 J kg-1K-1 (for 2.5T) is achieved, which is the largest reported to date for magnetocaloric HEAs. When compared to conventional high-performance magnetocaloric materials, our work is observed to be comparable to many of the conventional systems, closing the gap between magnetocaloric HEAs versus conventional magnetocaloric materials for the first time. This opens a new path for the search of functional materials with the optimal mechanical properties of HEAs.

 

 

ACTA

Vol. 212，15 Jun. 2021, 116933

9. Influence of microstructure and atomic-scale chemistry on the direct reduction of iron ore with hydrogen at 700°C

铁矿石在700℃氢气还原过程中的微观结构和成分演化

 

Se-Ho Kim, Xue Zhang, Yan Ma, Isnaldi R. Souza Filho, Kevin Schweinar, Katja Angenendt, Dirk Vogel, Leigh T. Stephenson, Ayman A. El-Zoka, Jaber Rezaei Mianroodi, Michael Rohwerder, Baptiste Gault✉, Dierk Raabe✉

B. Gault：b.gault@mpie.de

D. Raabe：d.raabe@mpie.de

https://doi.org/10.1016/j.actamat.2021.116933

 

摘要

人们使用碳作为还原剂提炼矿石中的铁，而钢铁冶炼目前已经是最大的单一工业温室气体排放源之一。因此，使用氢作还原剂具有广阔的发展前景。尽管相关反应已经被研究了几十年，但其动力学仍不清楚，且原慢过程及其缓慢。矿石的微观结构和局部化学性质限制了反应速率。我们对采用纯H2从赤铁矿中炼铁过程中矿石的结构和成分演变进行了研究。在还原过程中，由于氧的减少和非体积守恒相变，矿石中产生了复杂的孔隙和结构演变。还原后的高纯铁中含有孔隙和裂纹。我们观察到了几种晶格缺陷，这些缺陷对传质有加速作用，以及多种杂质元素(Na, Mg, Ti, V)以未被还原的氧化物岛形式存在。本研究对低碳铁生产过程具有重要意义。

向上滑动阅览英文摘要

Steel is the most important material class in terms of volume and environmental impact. While it is a sustainability enabler, for instance through lightweight design, magnetic devices, and effiffifficient turbines, its primary production is not. Iron is reduced from ores by carbon, causing 30% of the global CO2 emissions in manufacturing, qualifying it as the largest single industrial greenhouse gas emission source. Hydrogen is thus attractive as alternative reductant. Although this reaction has been studied for decades, its kinetics is not well understood, particularly during the wüstite reduction step which is much slower than hematite reduction. Some rate-limiting factors of this reaction are determined by the microstructure and local chemistry of the ores. Here, we report on a multi-scale structure and composition analysis of iron reduced from hematite with pure H2, reaching down to near-atomic scale. During reduction a complex pore- and microstructure evolves, due to oxygen loss and non-volume conserving phase transformations. The microstructure after reduction is an aggregate of nearly pure iron crystals, containing inherited and acquired pores and cracks. We observe several types of lattice defects that accelerate mass transport as well as several chemical impurities (Na, Mg, Ti, V) within the Fe in the form of oxide islands that were not reduced. With this study, we aim to open the perspective in the field of carbon-neutral iron production from macroscopic processing towards better understanding of the underlying microscopic transport and reduction mechanisms and kinetics.

 

 

ACTA

Vol. 212，15 Jun. 2021, 116880

10. In situ study of non-equilibrium solidification of CoCrFeNi high-entropy alloy and CrFeNi and CoCrNi ternary suballoys

CoCrFeNi、CrFeNi和CoCrNi合金非平衡凝固的原位研究

 

Angelo F. Andreoli✉, Olga Shuleshova, Victor T. Witusiewicz, Yuhao Wu, Yanzhao Yang, Oleh Ivashko, Ann-Christin Dippel, Martin v. Zimmermann, Kornelius Nielsch, Ivan Kaban✉

A.F. Andreoli：a.fernandes.andreoli@ifw-dresden.de

I. Kaban：i.kaban@ifw-dresden.de

https://doi.org/10.1016/j.actamat.2021.116880

 

摘要

我们利用高速视频和同步X射线衍射技术，对CoCrFeNi、CrFeNi和CoCrNi三种高熵/中熵合金的凝固行为进行了原位研究。在所有合金中，如果熔体过冷度较高，则可以观察到初生亚稳BCC相的形成。稳定FCC相在BCC晶体中形核的孕育期与熔体过冷度成反比。相关的稳态和亚稳态相图计算证实了实验结果。基于高速视频技术得到的CrFeNi、CoCrNi和CoCrFeNi晶体生长素体与文献中Fe-Ni和Fe-Cr-Ni合金的数据相当，两者具有相同的结晶动力学。此外，我们分析和讨论了熔体过冷对凝固样品组织的影响。

向上滑动阅览英文摘要

The solidification behavior of the CoCrFeNi high-entropy alloy and the ternary CrFeNi and CoCrNi medium-entropy suballoys has been studied in situ using high-speed video and synchrotron X-ray diffraction on electromagnetically levitated samples. In all alloys, the formation of a primary metastable bcc phase was observed if the melt was sufficiently undercooled. The delay time for the onset of the nucleation of the stable fcc phase, occurring within bcc crystals, is inversely proportional to the melt undercooling. The experimental findings are corroborated by thermodynamic calculations of stable and metastable phase diagrams for the (CoCrNi)-Fe section. Crystal-growth velocities for the CrFeNi, CoCrNi, and CoCrFeNi medium- and high-entropy alloys extracted from the high-speed video sequences in the present study are comparable to the literature data for Fe-rich Fe-Ni and Fe-Cr-Ni alloys, evidencing the same crystallization kinetics. The effect of melt undercooling on the microstructure of solidified samples is analyzed and discussed.

 

 

ACTA

Vol. 212，15 Jun. 2021, 116920

11. Intercritical annealing of cold-rolled ferrite-pearlite steel: Microstructure evolutions and phase transformation kinetics

冷轧珠光体-铁素体钢临界退火过程中的组织演变和相变动力学研究

 

J. Teixeira✉, M. Moreno✉, S.Y.P. Allain✉, C. Oberbillig✉, G. Geandier✉, F. Bonnet✉

J. Teixeira：julien.teixeira@univ-lorraine.fr

M. Moreno：m_moreno@hotmail.fr

S.Y.P. Allain：sebastien.allain@univ-lorraine.fr

C. Oberbillig：carla.oberbillig@arcelormittal.com

G. Geandier：guillaume.geandier@univlorraine.fr

F. Bonnet：frederic.bonnet@arcelormittal.com

https://doi.org/10.1016/j.actamat.2021.116920

 

摘要

冷轧铁素体珠光体(F/P)组织的退火是双相钢制备的关键步骤，涉及许多相互作用的机制，即铁素体的回复/再结晶、球化、锰的富集、渗碳体的粗化和奥氏体相变。我们重点研究了奥氏体转变，考虑了奥氏体与铁素体再结晶的相互作用以及渗碳体化学成分的影响。我们通过组织观察和原位高能X射线衍射研究了冷轧F/P组织在三种加热速率下的演变，以阐明不同机制之间的相互作用。结果表明，奥氏体在缓慢加热条件下呈链状，而在快速加热条件下呈带状。铁素体基体中大量的晶间(或孤立的)碳化物是导致这种特殊的组织形貌的主要原因。这些碳化物是在热轧过程中形成的。渗碳体成分的热动力学分析表明，珠光体相变过程中发生置换型元素的配分。而孤立碳化物的溶解则在加热过程中由配分型相变变为无配分相变。渗碳体溶解后，发生铁素体-奥氏体相变，相变动力学随加热速率的增加而增加。我们通过DICTRA软件对相变动力学进行了模拟和解释。

向上滑动阅览英文摘要

The manufacturing of Dual-Phase steels includes as a crucial step the annealing of a cold-rolled ferritepearlite (F/P) microstructure, which involves numerous and interacting metallurgical mechanisms, namely recovery/recrystallization of ferrite, globularization, manganese enrichment, coarsening of cementite and finally austenite transformation. Present study focuses on the austenite transformation considering its interaction with the ferrite recrystallization and the influence of the chemical composition of the cementite. The behavior of a cold-rolled F/P microstructure is studied at three heating rates to induce weak and strong interactions between the mechanisms, in particular using post mortem microstructure observations but also in situ High Energy X-Ray Diffraction experiments on a synchrotron beamline. Slow heating leads to a necklace austenite distribution whereas fast heating conducts to a banded topology. This particular microstructure morphogenesis is explained by the presence of numerous intergranular (or isolated) carbides inside the ferrite matrix, inherited from the hot-rolling. Thermokinetic analysis accounting for the cementite composition shows that the pearlite islands transformation necessarily involves the partition of substitutional elements. Conversely, the dissolving isolated carbides undergo a partition/partitionless transition on heating. After the dissolution of the cementite, a final ferrite/austenite transformation takes place. The phase transformation kinetics increases with increasing heating rates, despite the thermal-activated nature of the austenite growth process. This is interpreted thanks to kinetic simulations with DICTRA software, which allow to analyze the austenite growth regimes involving or not the partition of the alloying elements.