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

2021-06-04 来源：GS_Metals

 

本期包含金属材料领域论文13篇，涵盖了形状记忆合金、不锈钢、高熵合金、高温合金等，国内科研单位包括哈尔滨工业大学、台湾国立交通大学、浙江大学等（通讯作者单位）。

 

Vol. 206 目录

1. Competing Interactions between Mesoscale Length-Scales, Order-Disorder, and Martensitic Transformation in Ferromagnetic Shape Memory Alloys

铁磁形状记忆合金中中尺度相变、有序-无序转变和马氏体相变之间的相互竞争

 

2. Role of Hydrogen in the Separation of Interfaces in S13Cr Supermartensitic Stainless Steel

氢在S13Cr超级马氏体不锈钢界面失效中的作用

 

3. Enhanced strength in pure Ti via design of alternating coarse- and fine-grain layers

通过粗晶、细晶交替叠层结构设计提高纯钛的强度

 

4. Effect of thermal stress on anisotropic grain growth in nano-twinned and un-twinned copper films

热应力对纳米孪晶和无孪晶铜薄膜中晶粒各向异性长大的影响

 

5. Characteristics and mechanisms of hydrogen-induced quasi-cleavage fracture of lath martensitic steel

板条马氏体钢氢致准解理断裂的特征及机理研究

 

6. Mechanical response of dislocation interaction with grain boundary in ultrafine-grained interstitial-free steel

超细晶无间隙钢中位错与晶界的相互作用和力学响应研究

 

7. Chemical-Affinity Disparity and Exclusivity Drive Atomic Segregation, Short-Range Ordering, and Cluster Formation in High-Entropy Alloys

化学亲和力差异和排斥对高熵合金中元素偏聚、短程有序和团簇形成的驱动作用

 

8. The nucleation sequence of α-Al on TiB2 particles in Al-Cu alloys

Al-Cu合金中α-Al在TiB2颗粒上的形核顺序研究

 

9. The nature of yielding and anelasticity in metals

金属屈服和滞弹性的本质

 

10. Critical cooling rates for amorphous-to-ordered complexion transitions in Cu-rich nanocrystalline alloys

富铜纳米合金中非晶-有序转变的临界冷却速率

 

11. Formative and controlled mechanisms of nano-sized γ′ precipitates with local phase-transition within dislocation networks of nickel-based single crystal superalloys

镍基单晶高温合金中位错网络局域相变过程中纳米γ′析出的形成及控制机制

 

12. Deformation modes during room temperature tension of fine-grained pure magnesium

细晶纯镁室温拉伸的形变模式研究

 

13. Enhancing the flow resistance and sound absorption of open-cell metallic foams by creating partially-open windows

通过开窗设计增强金属泡沫的流体阻力和吸声能力

 

 

ACTA

Vol. 206，1 Mar. 2021, 116616

1. Competing Interactions between Mesoscale Length-Scales, Order-Disorder, and Martensitic Transformation in Ferromagnetic Shape Memory Alloys

铁磁形状记忆合金中中尺度相变、有序-无序转变和马氏体相变之间的相互竞争

 

D. Salas, Y. Wang, T.C. Duong, V. Attari, Y. Ren, Y. Chumlyakov, R. Arróyave, I. Karaman✉

I. Karaman：ikaraman@tamu.edu

https://doi.org/10.1016/j.actamat.2020.116616

 

摘要

我们研究了NiCoMnIn超磁形状记忆合金的组成、热处理及由此引起的组织演化对其马氏体相变和铁磁转变的影响。这一合金体系在较宽的温度范围内进行热处理过程中，都可观测到马氏体相变起始温度随热处理时间呈非单调变化，且这种非单调变化的特征也根据成分不同而不同。这一行为不能简单地用析出、析出引起的局部成分变化和/或材料整体的有序度变化解释。在此，我们通过系统的制备、热处理、热物性能测量、透射电子显微镜和原位同步X射线衍射表征，对非单调变化的铁磁转变和马氏体相变温度，与有序-无序转变引起的L21畴演化之间的关系进行了研究。将磁性-结构转变的热力学模型与经典形核理论相结合，进一步确定了组织的空间尺度对马氏体相变开始温度的影响。本研究为基于热力学和动力学对NiCoMnIn超磁形状记忆合金的耦合磁性-结构转变进行调控提供了指导。

向上滑动阅览英文摘要

In the present work, the effects of composition and heat treatments and the resulting microstructural changes on the martensitic transformation and ferromagnetic transition have been investigated in NiCoMnIn metamagnetic shape memory alloys. In this shape memory alloy system, it is observed that upon heat treatments at a wide temperature range, the onset temperature of the martensitic transformation follows a non-monotonic behavior with respect to heat treatment time, and the nature of the non-monotonic behavior is also a function of composition. This behavior cannot be attributed to well-known factors such as precipitation, change in local composition due to the precipitation and/or global degree of order. In this work, a systematic investigation through synthesis, thermal processing and characterization via thermo-physical measurements, transmission electron microscopy and in-situ synchrotron x-ray diffraction experiments has been used to correlate the non-monotonic dependence of the martensitic transformation and ferromagnetic transition temperatures to the evolution of L21 domains arising from a order/disorder phase transition. A thermodynamic model for the magneto-structural transition is combined with classical nucleation theory to further ascertain the role of microstructural length-scales on the onset of the martensitic transformation. This work thus provides understanding of the thermodynamic and kinetic factors that can be controlled to tune the coupled magneto-structural transformations in NiCoMnIn metamagnetic shape memory alloys.

 

 

ACTA

Vol. 206，1 Mar. 2021, 116614

2. Role of Hydrogen in the Separation of Interfaces in S13Cr Supermartensitic Stainless Steel

氢在S13Cr超级马氏体不锈钢界面失效中的作用

 

Debora Lima Molter, Mario Augusto Lopes de Castro, Dilson Silva dos Santos✉

D. Silva dos Santos：dilson@metalmat.ufrj.br

https://doi.org/10.1016/j.actamat.2020.116614

 

摘要

我们对S13Cr超级马氏体不锈钢(SMSS)在不同阴极电位下进行了氢脆(HE)实验和数值分析。我们采用双恒电位法(DPM)和步进法(SM)两种电化学技术以及热吸收光谱(TDS)研究了氢的扩散行为，测得表观氢扩散系数为1.4 × 10−13 ~ 4.7 × 10−12 m2/s。TDS实验表明存在较深的H陷阱，例如析出相界面、残余奥氏体/铁素体界面等。我们通过拉伸试验和断口分析，研究了氢脆对材料韧性的影响。在-1.5 V/SCE和-1.7 V/SCE的预充测试样品中，延伸率最大降低约14%，且沿整个截面观察到大量脆性断裂。我们基于试验数据，进行了有限元模拟，对韧性损失进行了预测。模型采用了静态结构条件下的断裂控制方法，在试样延伸率的降低与临界断裂能的降低之间建立联系，其中临界断裂能的降低通过热力学过剩变量的平均场方法计算得到。结果表明，S13Cr具有良好的抗氢脆性能，计算模型可靠，实验和模拟结果之间的误差约为5%。

向上滑动阅览英文摘要

This paper outlines experimental procedures and numerical analyses to investigate hydrogen embrittlement (HE) of S13Cr supermartensitic stainless steel (SMSS) subjected to various cathodic potentials. The hydrogen diffusion behavior was investigated using two electrochemical permeation techniques, namely, the double potentiostatic method (DPM) and the step method (SM), along with thermal desorption spectroscopy (TDS) tests. The apparent hydrogen diffusion coefficients varied from 1.4 × 10−13 to 4.7 × 10−12 m2/s, and TDS revealed the existence of deep traps, such as interfaces around precipitates and between retained austenite and ferritic matrix. The effects of HE in terms of a reduction in ductility were analyzed through tensile tests and fractographic analysis. A maximum reduction in elongation of approximately 14% was measured, and a majority of brittle fracture along the entire net section was observed in test samples pre-charged under -1.5 V/SCE and -1.7 V/SCE. A computational simulation was performed using the finite element method to predict the loss of ductility using the obtained experimental data. The computational model used a fracture-controlled method under static structural conditions, which links the reduction in elongation of the tensile specimens to the decrease in critical fracture energies, which, in turn, were calculated through a new mean field approach that used thermodynamic excess variables. The observations presented here suggest that S13Cr has good resistance to HE and that the computational model is reliable because only slight deviations in the magnitude (5%) were observed between the experimental and numerical results.

 

 

ACTA

Vol. 206，1 Mar. 2021, 116627

3. Enhanced strength in pure Ti via design of alternating coarse- and fine-grain layers

通过粗晶、细晶交替叠层结构设计提高纯钛的强度

 

Danyang Li, Guohua Fan✉, Xiaoxu Huang, Dorte Juul Jensen, Kesong Miao, Chao Xu, Lin Geng✉, Yubin Zhang, Tianbo Yu✉

G. Fan：ghfan@njtech.edu.cn（南京工业大学）

L. Geng：genglin@hit.edu.cn（哈尔滨工业大学）

T. Yu：tiyu@mek.dtu.dk

https://doi.org/10.1016/j.actamat.2021.116627

 

摘要

金属的屈服强度与平均晶粒尺寸有关，遵循Hall-Petch公式，而层状复合材料的强度则通常遵循混合规则(ROM)。在本研究中，我们制备了一种经特别设计的Ti基多层复合材料。该复合材料又交替的细晶层和粗晶层组成，且不论是细晶层还是粗晶层，层厚均与晶粒尺寸相当。材料实现了极高的屈服强度，远超Hall-Petch公式和混合规则的预测值。我们通过多种实验表征手段，包括使用纳米硬度仪测量硬度、使用拉伸过程中的原位同步辐射XRD测量晶格应变、使用TEM测量材料屈服后的位错结构，对这种多层复合材料的强化机制进行了研究。我们发现，粗晶层中层界面附近的硬度明显高于层中区域，屈服后只在界面区域观察到了<c+a>位错和密集的<a>位错堆积。这说明，在HCP材料的变形过程中，界面具有很强的约束作用，<a>滑移和<c+a>滑移的临界剪切应力之间存在较大差异。粗晶/细晶多层复合Ti结构可以同时实现细晶的强度和粗晶的韧性，这为单相HCP材料的性能优化提供了一种新的设计策略。

向上滑动阅览英文摘要

The yield strength of metals is typically governed by the average grain size through the Hall-Petch relation, and it usually follows the rule of mixture (ROM) for layered composite materials. In the present study, an extraordinarily high yield strength, far beyond the predicted values from the Hall-Petch relation and the ROM, is achieved in a specially designed layered titanium that is characterized by alternating coarse- and fine-grain layers (C/F-Ti) where the grain sizes match the layer thicknesses in both the coarse- and fine-grained layers. The strengthening mechanism of such a layered C/F-Ti is investigated based on detailed experimental characterizations, including nanoindentation tests of local hardness, in-situ synchrotron Laue X-ray microdiffraction (μXRD) measurement of the lattice strain distribution during tensile testing, and transmission electron microscopy (TEM) analysis of the dislocation structure after yielding. In the coarse-grain layers, significantly higher hardness values are observed next to the layer interfaces compared to the layer center regions, and <c+a> dislocations and densely populated pile-ups of <a> dislocations are exclusively observed in the interface regions after yielding. These experimental results point to an enhanced interface constraint effect on the deformation mechanism in hexagonal close-packed (hcp) materials with a large difference in the critical resolved shear stress between <a> slip and <c+a> slip. The C/F-Ti combines the strength of fine grains and the ductility of coarse grains, demonstrating a new structural design strategy for property optimization of single-phase hcp materials.

 

 

ACTA

Vol. 206，1 Mar. 2021, 116637

4. Effect of thermal stress on anisotropic grain growth in nano-twinned and un-twinned copper films

热应力对纳米孪晶和无孪晶铜薄膜中晶粒各向异性长大的影响

 

I-Hsin Tseng, Yun-Ting Hsu, Jihperng Leu, K N Tu, Chih Chen✉

C. Chen：chih@mail.nctu.edu.tw （台湾国立交通大学）

https://doi.org/10.1016/j.actamat.2021.116637

 

摘要

我们在Si基底上电化学沉积了3.8µm厚的特定取向的纳米孪晶铜(nt-Cu)。我们采用弯曲梁法在室温到400℃范围内对其进行了热应力测量，并研究了铜薄膜经热处理后的微观组织演化。结果表明，150℃时，最大压应力达到150 MPa，(111)取向的纳米孪晶铜开始向(200)取向转变。超过150°C，(200)晶粒的各向异性生长加快。我们发现，纳米孪晶铜薄膜能承受比无纳米孪晶的随机取向铜薄膜大1.5倍的压应力。这一巨大的热应力为定向纳米孪晶Cu晶粒的各向异性生长提供了驱动力，晶粒尺寸最终可达几百µm。

向上滑动阅览英文摘要

Oriented and nanotwinned copper (nt-Cu) of 3.8 µm thickness was electroplated on a Si wafer substrate for thermal stress measurement from room temperature to 400 °C by bending beam method. Microstructure transformation in the copper thin film was studied after the thermal process. At 150 °C, the maximum compressive stress reached 150 MPa, and the (111) oriented nanotwinned copper began to transform to (200) orientation. Beyond 150 °C, anisotropic grain growth of (200) grains is faster. For comparison with the random-oriented copper thin films without nanotwins, we discover that the nanotwinned films can withstand a compressive stress of 1.5 times greater than the random copper thin films. This large thermal stress provides the driving force for anisotropic grain growth in the oriented nano-twin Cu, which can reach several hundred µm.

 

 

ACTA

Vol. 206，1 Mar. 2021, 116635

5. Characteristics and mechanisms of hydrogen-induced quasi-cleavage fracture of lath martensitic steel

板条马氏体钢氢致准解理断裂的特征及机理研究

 

L. Cho✉, P.E. Bradley, D.S. Lauria, M.L. Martin, M.J. Connolly, J.T. Benzing, E.J. Seo, K.O. Findley, J.G. Speer, A.J. Slifka

L. Cho：lawrence.cho@nist.gov, cyc616@postech.ac.kr

https://doi.org/10.1016/j.actamat.2021.116635

 

摘要

我们对淬火态22MnB5的板条马氏体组织、晶体取向和氢致准解理断裂下的位错进行了深入表征。我们采用了扫描电子显微镜(SEM)、背散电子衍射(EBSD)、透射电子显微镜(TEM)、透射菊池衍射(TKD)等多种手段对氢脆马氏体试样的断口进行了分析。氢影响区的主要断裂方式为准解理断裂，撕裂脊附近有塑性区，准解理面存在高密度位错。马氏体的组织尺寸、变体取向和界面均对准解理表面形貌有一定影响。断口形貌表明，{100}α'理穿过马氏体板条，随后演化为相对“平坦”的准解理面，同时板条和区块边界处出现{110}α'裂纹，并沿非解理面断裂。随着马氏体组织尺寸的增大，形成相对“平坦”的准解理面的可能性也增大。在氢致解理断裂{100}α'面的断口下方，马氏体区块内的{112}α'滑移面上形成了大量的位错带。我们发现，准解理面上的河流条纹起源于复杂且层次分明的板条马氏体组织。准解理面上的台阶和脊通常与各种马氏体界面相连，表明它们是由于裂纹在这些边界处的偏离而产生的。我们基于Cottrell解理模型，结合氢的作用，对马氏体的准解理机制和断裂路径进行了讨论。

向上滑动阅览英文摘要

 

This study presents an in-depth characterization of the microstructures, crystallographic orientations, and dislocation characteristics beneath hydrogen-induced quasi-cleavage fracture features of an as-quenched, lath martensitic (α') 22MnB5 steel. The fracture surfaces of gaseous hydrogen-embrittled martensitic specimens were analyzed by a combination of multiple analytical tools: scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and transmission Kikuchi diffraction (TKD). The dominant fracture mode in the hydrogen-affected zones was quasi-cleavage fracture, which involved significant plasticity, evidenced by plastic zones near tear ridges and a high density of dislocations beneath the quasi-cleavage facets. The martensite constituent sizes, variant orientations, and boundaries influenced the quasi-cleavage surface morphologies. Fractography revealed the occurrence of {100}α'-type cleavage across martensitic laths, developing relatively “flat” quasi-cleavage surfaces, in addition to {110}α'-type cracking likely along lath and block boundaries, and fracture along non-cleavage planes. The likelihood of the formation of the relatively “flat” quasi-cleavage surfaces increased with increasing martensitic constituent sizes. Substantial dislocation bands formed on intersecting {112}α' slip planes within a martensite block below the hydrogen-induced cleavage fractures on {100}α' planes. River markings on the quasi-cleavage surfaces were found to originate from the complex, hierarchical lath martensitic microstructure. Steps and ridges on the quasi-cleavage facets generally linked with the various martensitic boundaries, suggesting that they were produced as a result of crack deviations at those boundaries. The fracture paths and martensite quasi-cleavage mechanisms are discussed in the context of the role of hydrogen and Cottrell cleavage model.

 

 

ACTA

Vol. 206，1 Mar. 2021, 116621

6. Mechanical response of dislocation interaction with grain boundary in ultrafine-grained interstitial-free steel

超细晶无间隙钢中位错与晶界的相互作用和力学响应研究

 

Hongxing Li✉, Si Gao, Yo Tomota, Seiichiro Ii, Nobuhiro Tsuji, Takahito Ohmura

H. Li：Li.Hongxing@nims.go.jp

https://doi.org/10.1016/j.actamat.2021.116621

 

摘要

我们以超细晶(UFG)无间隙(IF)钢为研究对象，阐明了Hall-Petch曲线表现出的“超硬化”行为和轴向拉伸试验中不连续屈服行为的潜在机制。我们采用透射电子显微镜(TEM)对不同拉伸应变下的超细晶IF钢试样进行了观察，发现在宏观屈服前，1.0%的微观拉伸应变后，晶粒内部的位错密度降低。宏观屈服后，晶粒内部位错密度增大，最终颈缩区的微观拉伸应变为15%。我们通过TEM微柱原位压缩试验，对超细晶IF钢中的位错运动及其与晶界的相互作用进行了直接观测。宏观屈服前，晶内位错向晶界移动，在晶界处被吸收。在预屈服过程中，位错密度由于湮没而显著降低，同时伴随载荷增加。微柱晶粒内位错密度的降低与块体样品中的观测结果一致。宏观屈服后，晶界处出现爆发式的位错发射，导致了屈服应力降低和不连续屈服行为。通过结合Orowan模型和Johnston-Gilman模型，可以较好地从位错密度的变化的角度，理解超细晶IF钢的高屈服应力和屈服下降行为。

向上滑动阅览英文摘要

Interstitial-free (IF) steel with ultrafine-grained (UFG) size was used to clarify the underlying mechanisms of the ‘extra-hardening’ behavior from the Hall-Petch plot and the discontinuous yielding behavior from axial tensile tests. Using transmission electron microscopy (TEM) at different tensile strains, it was found that the TEM micrographs for the bulk sample of the UFG IF steel showed a decrease in dislocation density in the grain interior after experiencing a micro tensile strain of 1.0% before macro-yielding. Additionally, an increase in dislocation density was found in the grain interior, with a micro tensile strain of 15% in the necking region after macro-yielding. In-situ compression tests in a TEM for micropillars were performed to directly observe the motion of dislocations and corresponding interactions with grain boundaries in UFG IF steel. Before macro-yielding, pre-existing dislocations in the grain interior moved toward the grain boundary, wherein they were then absorbed. The dislocation density decreased significantly due to the annihilation, which was accompanied by an increase in load during pre-yielding. The decrease in dislocation density in the grain interior of the micropillar is consistent with the results obtained from the bulk sample. After macro-yielding, the burst-like dislocation emission emerged from the grain boundary, leading to a yield drop and a discontinuous yielding behavior. Furthermore, the higher yield stress and the yield drop in the UFG IF steel can be understood by the decrease in dislocation density according to a combination of the Orowan model as well as the Johnston-Gilman model.

 

 

ACTA

Vol. 206，1 Mar. 2021, 116638

7. Chemical-Affinity Disparity and Exclusivity Drive Atomic Segregation, Short-Range Ordering, and Cluster Formation in High-Entropy Alloys

化学亲和力差异和排斥对高熵合金中元素偏聚、短程有序和团簇形成的驱动作用

 

Shuai Chen, Zachary H. Aitken, Subrahmanyam Pattamatta, Zhaoxuan Wu, Zhi Gen Yu, Rajarshi Banerjee, David J. Srolovitz✉, Peter K. Liaw✉, Yong-Wei Zhang✉

D.J. Srolovitz：srol@cityu.edu.sg（香港城市大学）

P.K. Liaw：pliaw@utk.edu

Y.-W. Zhang：zhangyw@ihpc.a-star.edu.sg

https://doi.org/10.1016/j.actamat.2021.116638

 

摘要

根据已有文献报导，在实验中观察到了高熵合金(HEAs)中的元素偏聚、近程有序和团簇形成。原子大小和元素的电负性差异被认为是这类现象的根本原因。我们使用了蒙特卡罗方法结合分子动力学模拟，对于两种高熵合金，CoCuFeNiPd和CoCuFeNiTi，进行了研究。结果表明，尽管Ti与其它元素之间的尺寸及电负性差异比Pd大，但CoCuFeNiPd中的元素偏聚和短程有序比CoCuFeNiTi更加显著，这表明仅仅原子尺寸和电负性的差异不足以解释模拟结果。我们发现，Ti（Pd）与其他元素之间的化学亲和力的差异和排斥性引起了这两种合金中不同的聚类行为。我们确定了出现显著元素偏聚和近程排序的三个条件：1. 化学元素之间的化学亲和力差异较大 ；2. 低、中、高能团簇具有较高的化学元素排斥性；3. 中、低能量团簇的形成会导致体系的能量减少，从而补偿高能团簇形成导致的能量增加。我们的研究结果与文献中报道的实验结果一致，强调了化学亲和力差异和排斥性高熵合金微观组织的影响，解释了高熵合金中高能团簇的成因，为高性能高熵合金的设计提供了指导。

向上滑动阅览英文摘要

Recently, atomic segregation, short-range ordering, and cluster formation have been observed experimentally in high-entropy alloys (HEAs). Differences in the atomic size and electronegativity of constituent elements were proposed to be the underlying cause of such ordering. Here, we investigated two HEAs, CoCuFeNiPd and CoCuFeNiTi, using a combination of Monte Carlo and molecular dynamic simulations. Our results show that the CoCuFeNiPd HEA exhibits much stronger atomic segregation and short-range ordering than the CoCuFeNiTi HEA, despite the larger differences in the relative atomic size and electronegativity of Ti with other constituent elements, as compared to those of Pd, suggesting that the differences in the atomic size and electronegativity alone are insufficient to explain the simulation results. We find that it is the chemical-affinity disparity and exclusivity between Ti (Pd) with the remaining species that lead to the different clustering behavior in these two HEAs. Specifically, three conditions for strong atomic segregation and short-range ordering are identified: 1. a large chemical-affinity disparity amongst the chemical elements; 2. a high chemical-element exclusivity in low-, medium-, and high-energy clusters; and 3. a net energy reduction associated with low- and medium-energy-cluster formation that compensates for the energy increase associated with high-energy-cluster formation. Our findings are in agreement with experimental results reported in literature, and highlight the importance of chemical-affinity disparity and exclusivity in influencing the microstructure of HEAs, explain the origin of high-energy-cluster formation in HEAs, and provide guidelines for designing HEAs with excellent properties.

 

 

ACTA

Vol. 206，1 Mar. 2021, 116652

8. The nucleation sequence of α-Al on TiB2 particles in Al-Cu alloys

Al-Cu合金中α-Al在TiB2颗粒上的形核顺序研究

 

Jiehua Li✉, Fredrik S. Hage, Quentin M. Ramasse, Peter Schumacher

J. Li：jiehua.li@unileoben.ac.at

https://doi.org/10.1016/j.actamat.2021.116652

 

摘要

近几十年来，TiB2对铝合金的细化作用在工业界和学术界都得到了广泛的研究。为了获得更好的晶粒细化能力，需要添加其他溶质元素，从而对TiB2颗粒界面处的非均匀形核进行调控。在此，我们报导了Al-Cu合金中TiB2非均匀形核界面的原子尺度实验结果，以及Al-5Ti-1B对Al-Cu合金的细化作用。其中着重研究了主要溶质元素(Ti、Cu)的偏聚对TiB2界面的影响，并试图其与其他成核、长大的影响因素分开。在Al-5Ti-1B细化剂中，TiB2粒子的基面上可以明显观察到Ti的偏聚，这一富Ti层为Al3Ti二维化合物，这与之前文献中的记录一致。在Al-Cu合金体系中，TiB2基面也普遍存在Ti的偏聚，当Cu浓度较高时，还存在原子尺度的富Cu层。基于以上观察，我们在添加了Al-5Ti-1B晶粒细化剂的Al-Cu合金中，提出了一种可能的成核顺序。Al在TiB2的富Ti层表面形核，当Cu含量足够时，这些核心借助共晶反应形成一层富Cu层，从而在随后的包晶反应中被保存下来。这一形核顺序有可以帮助我们在TiB2基面上的Al3Ti层与凝固后的工艺条件之间建立联系。虽然很难确切地知道，在凝固后组织中观测到的TiB2粒子在多大程度上对凝固过程中的非均匀形核起到了激活作用，但本研究着重强调了Cu的偏聚在Al-5Ti-1B细化Al-Cu 合金晶粒过程中的作用。

向上滑动阅览英文摘要

The refinement of Al alloys by TiB2 has been extensively investigated for decades, both in industry and academia. In order to achieve higher grain refinement potency, it is known that other solutes must be added alongside TiB2, thus tailoring the heterogeneous nucleation at the interface between the TiB2 particles and the Al matrix. Here, we report results from an atomic-scale experimental investigation of the heterogeneous nucleation interface of TiB2 in Al-Cu based alloys as well as in an Al-5Ti-1B grain refiner employed in these Al-Cu based alloys. We focus on the effect of segregation of the main solute elements (Ti, Cu) to the interface of TiB2 and attempt to disentangle this effect from other factors affecting the nucleation and growth. Significant Ti segregation in the form of a Ti-rich layer, identified as an Al3Ti two-dimensional compound, was unambiguously observed on the basal plane of TiB2 particles in the Al-5Ti-1B grain refiner, in agreement with prior literature. In the Al-Cu alloy system, prevalent Ti segregation was also observed on the basal plane of TiB2, accompanied in cases when the Cu concentration is high by the presence of a further atomic-scale Cu-rich layer. Based on these observations, a possible nucleation sequence for the Al-Cu based alloys with the addition of Al-5Ti-1B grain refiner is proposed whereby Al nucleation occurs on an Ti-rich layer on the surface of TiB2, which can then be preserved from a subsequent peritectic transformation by a surrounding eutectic reaction that forms a Cu-rich layer when sufficient Cu is present. This proposed nucleation sequence should help to link the absence or presence of Al3Ti layers on the basal plane of TiB2 to processing conditions in post-solidification studies. Although it is difficult to know with absolute certainty if a TiB2 particle observed in the post-solidification microstructure was active or inactive for heterogeneous nucleation during the solidification process, this experimental study highlights the possible role of Cu segregation on grain refinement of Al-Cu alloys by the Al-5Ti-1B grain refiner.

 

 

ACTA

Vol. 206，1 Mar. 2021, 116625

9. The nature of yielding and anelasticity in metals

金属屈服和滞弹性的本质

 

Dayong Li, Robert H. Wagoner✉

R.H. Wagoner：wagoner.2@osu.edu

https://doi.org/10.1016/j.actamat.2021.116625

 

摘要

最近有文献指出，金属在所有应力条件下，屈服前的应力-应变曲线总存在一定的非线性和迟滞性。这使得我们需要思考金属变形的中的一些基本问题。是否存在一个临界应力，在该应力以下位错是不动的？是否存在一个发生永久形变对应的临界应力？滞弹性和弹性、塑性有什么区别？为此，我们对11种商用合金板材（9种高强钢、2种Mg合金）施加了不同的预应变，随后进行了加载-卸载循环拉伸试验。我们提出了一个位错滞弹性耗散模型，模型与实验结果吻合较好。我们发现，材料施加预应变后，存在一个有限的屈服应力，在此应力之下不会发生永久变形或硬化。滞弹性不同于弹性和塑性：它是可恢复和耗散的；机械可逆而热力学不可逆。相应的初始加载试验得出了截然不同的结论。没有预应变时，材料在近零应力下，即发生塑性变形。基于以上结果，我们对弹性、塑性和滞弹性变形的局部和非局部相互作用提出了假设。

向上滑动阅览英文摘要

Recent reports in the literature identified pre-yield stress-strain nonlinearity and hysteresis (anelasticity) as occurring in metals at virtually all stresses. These observations raise foundational questions about metal deformation. Does a critical stress exist below which dislocations are immobile? Is there a critical stress for which permanent deformation occurs? Is anelasticity distinct from elasticity and plasticity? To answer such questions, special tensile tests with loading-unloading cycles after various prestrains were performed for 11 commercial sheet alloys: 9 AHSS (advanced high strength steels) and two Mg alloys. A dissipative dislocation bow-out model of anelasticity was derived that closely reproduces the experimental results and is consistent with the evolving experimental picture of anelasticity. Following prestrain, a finite yield stress was found to exist, below which no permanent deformation or hardening occurs. Anelasticity is distinct from elasticity and plasticity: it is recoverable and dissipative; mechanically reversible and thermodynamically irreversible. Corresponding tests of initial loading suggest radically different conclusions. Without prestrain, i.e. without a developed internal stress pattern, plastic deformation occurs near zero stress. A postulate of local and nonlocal interactions accounting for elastic, plastic and anelastic deformation was proposed.

 

 

ACTA

Vol. 206，1 Mar. 2021, 116650

10. Critical cooling rates for amorphous-to-ordered complexion transitions in Cu-rich nanocrystalline alloys

富铜纳米合金中非晶-有序转变的临界冷却速率

 

Charlette M. Grigorian, Timothy J. Rupert✉

T.J. Rupert：trupert@uci.edu

https://doi.org/10.1016/j.actamat.2021.116650

 

摘要

纳米晶金属中的非晶相能够提高材料的机械性能、抗辐照性能以及抑制晶粒长大。本文通过观察从高温冷却过程中，冷却速率对二元和三元铜基合金非晶态-有序态相变的影响，研究了非晶相的稳定性。我们首先对Cu-Zr和Cu-Zr- hf合金试样进行了退火使晶界预熔，随后将样品进行淬火。淬火过程中，采取特殊工艺使试样高度方向的局部冷却速度存在梯度。研究发现，Cu-Zr- hf合金中的非晶厚度分布与局部冷却速率无关，而Cu-Zr合金在缓慢冷却区的非晶层较薄，这表明Cu-Zr- hf合金中非晶相的稳定性优于Cu-Zr合金。我们基于实验结果绘制了二元和三元合金非晶态-有序态相变的时间-温度-相变图，加深了冷却速率和晶界化学对相变影响的认识。三元合金的临界冷却速率比二元合金至少慢三个数量级。

向上滑动阅览英文摘要

Amorphous complexions in nanocrystalline metals have the potential to improve mechanical properties and radiation tolerance, as well as resistance to grain growth. In this study, the stability of amorphous complexions in binary and ternary Cu-based alloys is investigated by observing the effect of cooling rate from high temperature on the occurrence of amorphous-to-ordered complexion transitions. Bulk Cu-Zr and Cu-Zr-Hf alloy samples were annealed to induce boundary premelting and then quenched through a procedure that induces a gradient of local cooling rate through the sample height. Amorphous complexion thickness distributions were found to be invariant to local cooling rate in the Cu-Zr-Hf alloy, demonstrating enhanced stability of the amorphous complexion structure compared to the Cu-Zr alloy, which had thinner amorphous complexions in the regions that were slowly cooled. The experimental results are used to construct time-temperature-transformation diagrams for the amorphous-to-ordered complexion transition in both the binary and ternary alloys, enabling a deeper understanding of the influence of cooling rate and grain boundary chemistry on complexion transitions. The critical cooling rate necessary to avoid complexion transitions in the ternary alloy is found to be at least three orders of magnitude slower than that for the binary alloy.

 

 

ACTA

Vol. 206，1 Mar. 2021, 116653

11. Formative and controlled mechanisms of nano-sized γ′ precipitates with local phase-transition within dislocation networks of nickel-based single crystal superalloys

镍基单晶高温合金中位错网络局域相变过程中纳米γ′析出的形成及控制机制

 

Wanshun Xia, Xinbao Zhao✉, Quanzhao Yue, Liang Yue, Jiangwei Wang, Qingqing Ding, Hongbin Bei, Ze Zhang✉

X. Zhao：superalloys@zju.edu.cn（浙江大学）

Z. Zhang：zezhang@zju.edu.cn（浙江大学）

https://doi.org/10.1016/j.actamat.2021.116653

 

摘要

我们对镍基单晶高温合金在1373K、137MPa蠕变过程中位错网络的成分和结构演化进行了研究。位错网络中的区域可分为两部分：网格线和中间的网格区域。随着位错网络的演化，网格区有纳米级γ′相(γ′n)析出，而网格线始终为FCC γ相。Cr、Co和Re在网格线处偏析增加，使网格区Al等γ′形成元素含量增加，引起了FCC-L12的局域相变，形成γ′n相。γ′n 的进一步长大需要大量的γ′形成元素扩散，然而这种扩散被网格线处Cr、Co、Re偏聚形成的化学屏障所阻挡。网格区域的γ′相和网格线处的γ相互相支撑，形成了一种稳定的蠕变位错结构。在较大的局部晶格失配条件下，枝晶内更容易形成更加致密的位错网络，从而促进γ/γ′亚结构的形成，提高材料的抗蠕变抗性能。

向上滑动阅览英文摘要

The chemical and structural evolution within dislocation networks are investigated in a nickel-based single crystal superalloy crept under 1373K and 137MPa. The local region within dislocation networks can be divided to two separated parts: gridlines which compose the arrangements of dislocation networks and mesh regions as intervals between gridlines. With evolution of dislocation networks, precipitation of nano-sized γ′ phase (γ′n) are observed in mesh region, while gridlines always display the FCC feature of γ phase. The formative mechanism of γ′n is revealed as increased segregations of Cr, Co and Re along gridlines which enhance the contents of γ′-rich elements such as Al in mesh region to promote the local phase transition from FCC to highly ordered L12. However, growth of γ′n requires massive diffusion of γ′-rich elements that is confined by the chemical barrier along gridlines with strong segregations of Cr, Co and Re. The mesh region of γ′n and gridlines of γ reinforce each other forming potential γ/γ′ substructures to stabilize the dislocation networks during creep. Denser dislocation networks formed in dendrite core under larger local lattice misfifit are accompanied with facilitated formation of γ/γ′ substructures which derive higher creep resistance than interdendritic region.

 

 

ACTA

Vol. 206，1 Mar. 2021, 116648

12. Deformation modes during room temperature tension of fine-grained pure magnesium

细晶纯镁室温拉伸的形变模式研究

 

Zhuoran Zeng✉, Mengran Zhou, Peter Lynch, Frédéric Mompiou, Qinfen Gu, Mohsen Esmaily, Yuanming Yan, Yao Qiu, Shiwei Xu, Hidetoshi Fujii, Chris Davies, Jian-Feng Nie, Nick Birbilis

Z. Zeng：zhuoran.zeng@anu.edu.au

https://doi.org/10.1016/j.actamat.2021.116648

 

摘要

挤压成型的细晶（晶粒尺寸~1.2 µm）多晶纯镁尽管存在较强的织构，但在室温下的延伸率仍可超过100%。在本研究中，我们通过多尺度原位表征技术揭示了其变形模式，以图揭示这种超塑性的成因。同步辐射XRD结果表明，当伸长率为55%时，细晶样品的弹性晶格应变比粗晶样品低3-10倍，表明细晶内没有明显的应变积累，样品内部没有晶间形变。原位SEM证实了晶间变形的主导作用，进一步揭示了晶间形变是由具有相似取向晶粒之间的相对滑移引起的。这种滑移引起的形变是巨大的，位于滑移晶粒组之间的晶粒通过旋转，使得位错滑移容易发生。原位TEM进一步证实了位错滑移的调节模式。位错容易向晶界滑移，并在晶界处湮灭。以上结果表明，细晶Mg的变形模式主要是由晶粒旋转和位错滑移导致的成组晶间滑移，这与粗晶Mg中的位错滑移模式显著不同。协调变形抑制了局部应力集中，从而大幅提高了纯Mg的室温塑性。

向上滑动阅览英文摘要

Extruded polycrystalline pure magnesium (Mg) with fine grain size (~1.2 µm) exhibits ductility of over 100% at room temperature, in spite of the presence of a strong basal texture. In this study, a set of complementary in-situ characterisation techniques over multiple-length scales were utilised to reveal the deformation modes enabling such ductility. Synchrotron X-ray diffraction results show that the elastic lattice strain of fine-grained sample for tensile elongation up to ~55% is 3–10 times lower than that in the coarse-grained sample, indicating the absence of significant strain accumulation inside fine grains and potential inter-granular deformation in bulk. In-situ scanning electron microscopy validates the predominant operation of the inter-granular deformation, and it further reveals that the inter-granular deformation occurs by the relative sliding between groups of grains having similar orientations. The deformation resulting from such sliding is substantial, and it is accommodated by the rotation of grains located between slid grouped grains, from hard to softer orientations to allowing dislocation slip to readily occur. The accommodating mode of dislocation slip is further supported by in-situ transmission electron microscopy observations. Dislocations glide readily to, and annihilate at, grain boundaries. The observations and direct evidences presented herein suggest that the major deformation mode is sliding between grouped grains that is accommodated by grain rotation and dislocation slip, in contrast to dislocation slip in coarse-grained Mg. The coordinated deformation processes postpone the occurrence of localised stress concentration and greatly increases the ductility of pure Mg at room temperature.

 

 

ACTA

Vol. 206，1 Mar. 2021, 116666

13. Enhancing the flow resistance and sound absorption of open-cell metallic foams by creating partially-open windows

通过开窗设计增强金属泡沫的流体阻力和吸声能力

 

Xiang Yu, Zhenbo Lu, Wei Zhai✉

W. Zhai：mpezwei@nus.edu.sg

https://doi.org/10.1016/j.actamat.2021.116666

 

摘要

具有高流体阻力的金属泡沫是一种实用的吸声材料。在此，我们报导了一种新型金属泡沫材料，该材料在相互连接的泡沫孔之间采用部分打开的窗口形貌，从而提高了流体阻力和吸声系数。这种组织是在制备过程中利用金属浆料的剪切剪薄行为形成的。我们还建立了一种新的微观组织模型，考虑了窗口处特定表面积的增加，以模拟这种新型泡沫材料的渗透率。模型的输入参数包括材料胞结构的几何形状，这一参数可以通过材料的形貌表征获取。结果表明，这种新型金属泡沫的流体阻力显著提高（1.5倍），且孔隙率损失较小（< 2.3%）。声学实验表明，材料在整个频率范围内的吸声系数均有所提升（平均为0.2）。以上研究展示了一种特殊微结构泡沫金属的设计方法，材料具有高流体阻力和高孔隙率(93%~97%)开路结构。提出的流体模型在其他的设计和表征方面也具有优异的应用潜力。

向上滑动阅览英文摘要

Metallic foams with high flow resistivity are of high interest as practical sound absorption materials. Herein, we report the novel open-cell metallic foams associated with a partially-open window morphology between interconnected pores for improved flow resistivity and sound absorption coefficient. Such a microstructure was produced through exploiting the shear thinning behavior of the metal slurry during the template replication fabrication process. A new microstructural model for permeability simulation is also developed for the new foam to account for the increased specific surface area from the windows. Input parameters to the model include cell geometries that are accessible via morphological characterization. Results showed that metallic foams with the window morphology have significantly increased flow resistivity (1.5 times) with little loss in porosity (< 2.3%). Impedance tube acoustic measurements confirmed such increments to improve the sound absorption coefficient (averaged as 0.2) throughout the entire frequency range. The concept explored in this study demonstrates a generic approach for the design of microstructure-specific foams with simultaneously increased flow resistance and a fully open-celled microstructure associated with high porosity (between 93%~97%). The proposed fluid model also has excellent potential to be adopted in a diverse range of applications for design and characterization.