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金属顶刊双语导读丨Acta Mater. Vol.195

2020-06-09 来源：Goal Science

        《Acta Materialia》本期（Volume 195, 15 August 2020）刊出9篇科研论文，涵盖高熵合金、铝铜合金、镁合金以及不锈钢等多个金属材料领域。

 

Vol. 195 目录

1. Dynamics of particle-assisted abnormal grain growth revealed through integrated three-dimensional microanalysis

集成三维微观尺度分析揭示第二相粒子对晶粒异常长大影响的动力学特征

 

2. Dislocations in {10-12} Twins in Mg: a Kinematic and Energetic Requirement

镁{10-12}孪晶中形成位错需要满足的动力学和能量要求

 

3. Kink Formation Process in Long-Period Stacking Ordered Mg-Zn-Y Alloy

长周期有序堆垛Mg-Zn-Y合金中的扭折形成过程

 

4. Diffusion, defects and understanding the growth of a multicomponent interdiffusion zone between Pt-modified B2 NiAl bond coat and single crystal superalloy

扩散、缺陷以及含铂B2 NiAl涂层与单晶高温合金间多组分互扩散区的长大

 

5. Twisting of pre-twinned α-Fe nanowires from mild to wild avalanche dynamics

孪晶 α-Fe 纳米线在扭转过程中从温和到剧烈的动力学“雪崩”

 

6. Effects of heat treatment and build orientation on the evolution of ϵ and α′ martensite and strength during compressive loading of additively manufactured 304L stainless steel

增材制造304L不锈钢热处理及打印方向对ϵ和α′组织演变和压缩性能的影响

 

7. Consideration of kinetics on intermetallics formation in solid-solution high entropy alloys

固溶态高熵合金中的金属间化合物形成动力学

 

8. Composition dependence of metallic glass plasticity and its prediction from anelastic relaxation – A shear transformation zone analysis

金属玻璃塑性的成分依赖以及基于非弹性弛豫的塑性预测——切变区分析

 

9. Radius-dependent homogeneous strain in uncoalesced GaN nanowires

非聚合GaN纳米线的径向相关均匀应变

 

 

ACTA Vol. 195, 15 Aug. 2020, P1-12

Dynamics of particle-assisted abnormal grain growth revealed through integrated three-dimensional microanalysis

集成三维微观尺度分析揭示第二相粒子对晶粒异常长大影响的动力学特征

 

Ning Lua, Jiwoong Kang, Nancy Senabulya, Ron Keinana, Nicolas Gueninchault, Ashwin J. Shahania

https://doi.org/10.1016/j.actamat.2020.04.049

 

摘要

        通常弥散分布在金属、陶瓷等多晶体材料中的第二相粒子会阻碍晶粒长大，使晶粒细化，提升材料的力学性能。然而，在较高温度下经常会观测到部分晶粒的优先长大或异常长大，使得材料的使用寿命大大降低。第二相粒子促进晶粒异常长大的成因和机理一直是学界争论的焦点。在本研究中，作者通过3D-XRD成像技术，揭示了Al-Cu模型合金中晶界和第二相粒子之间的复杂交互作用。在具有高度非随机分布粒子的体系中，观测到了晶粒的异常长大现象。初始晶粒尺寸受控于第二相粒子的集中分布情况，大晶粒往往产生在第二相粒子较少的区域，而某些特定尺寸的晶粒可能会“逃离”晶粒尺寸分布，与考虑了表面张力和粒子钉扎的理论模型预测结果一致。

英文摘要

Secondary-phase particles are routinely dispersed in metals and ceramics to prevent grain growth and take full advantage of the small grain size in the mechanical properties of polycrystals. Somewhat surprisingly, the preferential or abnormal growth of a few grains is observed in particle-containing systems at relatively high temperature, which will limit the lifetime of the material. The origins and mechanisms of particle-assisted abnormal grain growth are widely contested. Here, we employ integrated three-dimensional X-ray imaging to throw new light on the complex interactions between grain boundaries and particles in an Al–Cu alloy as a model system. We observe abnormal grain growth in the presence of a highly non-random distribution of particles. The incipient grain size is set by the local distribution of particles such that the larger grains come from particle-poor regions. Subsequently, grains with a size advantage may “run away” from the grain size distribution, in agreement with predictions from an analytical model that takes into account the competing capillary and particle pinning pressures.

 

 

ACTA Vol. 195, 15 Aug. 2020, P13-24

 

Dislocations in {10-12} Twins in Mg: a Kinematic and Energetic Requirement

镁{10-12}孪晶中形成位错需要满足的动力学和能量要求

 

 

Fulin Wang, Yejun Gu, Rodney J. McCabe, Laurent Capolungo, Jaafar A. El-Awady, Sean R.Agnew

https://doi.org/10.1016/j.actamat.2020.04.033

 

摘要

        根据已发表文献中关于密排六方金属中基体位错和{10-12}孪晶界相互作用的TEM和分子动力学研究结果，启发学界作出了如下猜想，即在孪晶中可以形成 柏氏矢量的位错。目前已有报道称，当基体中的基底位错被前进中的孪晶界扫过时，它们会转化为孪晶基底 I1层错上的分位错。在本研究中我们发现，从能量的角度而言，孪晶界附近的一对分位错在有在孪晶内形成一个 位错的倾向。原位TEM观测结果证实了这一假设，发现长位错偶极子的一端终止于孪晶界，另一端终止于I1 层错。产生的近似螺位错的位错偶极子是可滑动的，在某些情况下能够自我湮灭。因此，相较于利用一个高能量位错堆垛把两个位错通过一个孪晶界压成一个位错，位错更倾向于在孪晶界向基体内部迁移的过程中，在Mg的{10-12}孪晶中自发形成。这些观测结果有助于解释孪晶自身的后续变形，以及为什么它们在在塑性剪切应力集中的情况下特别容易表现出较大的脆性。

英文摘要

Consideration of published TEM and molecular dynamics studies of interactions between matrix dislocations and {10-12} twin boundaries (TB) in hexagonal close packed metals inspires a hypothesis regarding the formation of dislocations with Burgers vectors inside the twins. It was previously reported that when basal dislocations from the matrix are swept by an advancing TB, they are converted into partial dislocations bounding basal I1 stacking faults (SFs) within the twin. In the present work, we show that this dislocation configuration near TB renders it energetically favorable for a pair of partial dislocations to constrict into a dislocation within the twin. New in situ TEM observations confirm this hypothesis by revealing long dislocation dipoles terminated by the TB at one end and by I1 SFs within the twin at the other end. Finally, the resulting near-screw dislocation dipoles are observed to be glissile, enabling self-annihilation in some circumstances. Thus, rather than requiring a high energy dislocation pile-up to press two dislocations through a TB into a single dislocation, it is demonstrated that dislocations naturally form, within  {10-12} twins in Mg, as TB migrates into a matrix, which inevitably contains dislocations with Burgers vectors. These observations help to explain how the twins themselves may subsequently deform and why they may be particularly vulnerable to plastic, shear localization.

 

 

ACTA Vol. 195, 15 Aug. 2020, P25-34

Kink Formation Process in Long-Period Stacking Ordered Mg-Zn-Y Alloy

长周期有序堆垛Mg-Zn-Y合金中的扭折形成过程

 

英文摘要

The formation process of the kink bands in a directionally solidified, polycrystalline, long-period stacking ordered (LPSO) Mg85Zn6Y9 phase during compression deformation was investigated. In-situ compression observations by scanning electron microscopy and electron backscattered diffraction analysis revealed that regions with localized crystal orientation rotation appeared before ridge kinks formed as surface relief. In this paper, it is called as pre-kink The observed pre-kinks were composed of two separate regions rotated in opposite directions to each other and distinguished from one another by the three boundaries. A transmission electron microscopy observation revealed that the boundaries of the pre-kink are sub-boundaries consisting of edge dislocation array, and both its ends are terminated within the matrix. These characteristics match the reported that of regular ridge kink boundaries. In addition, while pre-kinks do not possess the ability of complete reversibility, its boundaries are capable of moving elastically.

 

 

ACTA Vol. 195, 15 Aug. 2020, P35-49

Diffusion, defects and understanding the growth of a multicomponent interdiffusion zone between Pt-modified B2 NiAl bond coat and single crystal superalloy

扩散、缺陷以及含铂B2 NiAl涂层与单晶高温合金间多组分互扩散区的长大

 

摘要

        在四元非均匀体系的条件下求解Onsager理论的相关方程是极其困难的，因此本研究采用了伪二元和伪三元扩散偶方法实验测定了B2-Ni(CoPt)Al体系中与组分有关的扩散系数，基于热力学选择合适的端元组分形成理想/近似理想的扩散分布。在有Co元素存在的情况下，Ni和Al的伪二元互扩散系数降低；而在有Pt元素存在的情况下，Ni和Al的伪二元互扩散系数增加。伪三元互扩散系数实验表明，在有Pt元素存在的条件下，主要的互扩散系数显著增加。同时交叉互扩散系数的变化较小，印证了组分间扩散相互作用的微小变化。与互扩散系数的变化相比，成分相关的热力学驱动力则表现出相反的趋势，Pt(Co)诱导的点缺陷浓度的改变可能起到主要作用。第一性原理计算表明，Pt的添加使Ni元素的空位浓度增加，降低了三重缺陷扩散机制的活化能。这些发现可以用于解释添加Pt元素导致B2-Ni(Pt)Al涂层和Rene N5单晶高温合金之间互扩散区厚度增加的现象。此外，EPMA和TEM分析揭示了富难熔元素的析出物长大过程。

英文摘要

Composition-dependent diffusion coefficients are determined in B2-Ni(CoPt)Al system following the pseudo-binary and pseudo-ternary diffusion couple methods, which would not be possible otherwise in a quaternary inhomogeneous material fulfilling the conditions to solve the equations developed based on the Onsager formalism. The end-member compositions to produce ideal/near-ideal diffusion profiles are chosen based on thermodynamic details. The pseudo-binary interdiffusion coefficients of Ni and Al decrease in the presence of Co but increase in the presence of Pt. The pseudo-ternary interdiffusion coefficients indicate that the main interdiffusion coefficients increase significantly in the presence of Pt. Marginal changes of the cross interdiffusion coefficients substantiate a minor change of the diffusional interactions between the components. The thermodynamic driving forces show opposite trends with respect to composition as compared to the changes of the interdiffusion coefficients advocating a dominating role of the Pt(Co)-induced modifications of point defect concentrations. DFT-based calculations revealed that Pt alloying increases the Ni vacancy concentration and decreases the activation energy for the triple defect diffusion mechanism. These findings explain the increase in the thickness of the interdiffusion zone between the B2-Ni(Pt)Al bond coat and the single crystal superalloy René N5 because of Pt addition. Furthermore, the EPMA and TEM analyses reveal the growth of refractory elements-enriched precipitates.

 

 

ACTA Vol. 195, 15 Aug. 2020, P50-58

Twisting of pre-twinned α-Fe nanowires from mild to wild avalanche dynamics

孪晶 α-Fe 纳米线在扭转过程中从温和到剧烈的动力学“雪崩”

 

摘要

        本研究利用分子动力学模拟了带有孪晶界的α-铁纳米线的扭转行为。扭转纳米线将导致孪晶璧上产生拓扑缺陷。当扭转角较小时，孪晶壁内会产生扭折扭折; 当扭转角较大时，会进一步在扭折之间形成结节。在扭转过程中，小扭转角条件下，扭折的运动表现为抽动且互不相关。抽动强度的概率密度函数近似为高斯分布，表现为一种“温和”的变形模式。当扭转角增大时，由于具有高密度结节的复杂孪晶模式的产生，扭折的动力学模式从温和变为剧烈。扭折的集体运动行为类似雪崩，其能量遵循幂律分布。剧烈程度可以通过在雪崩似的运动中应变能的释放比例进行描述，它与结节密度密切相关，并且同时受到外部长度范围（即纳米线直径）和内部长度范围（即孪晶界间距）的控制。在形成复杂孪晶之前卸载可使纳米线获得良好的应变-应力恢复能力。本研究将孪晶模式的演变与抽动过程的动力学统计分析联系起来，从而确定了纳米线中由孪晶边界运动所控制的独特力学特性。

英文摘要

We studied the torsion behavior of α-Fe nanowires seeded with twin boundaries (TBs) using molecular dynamics simulations. Twisting the wire generates topological defects in the twin walls, namely kinks inside the twin walls for small twist angles, and junctions between kinks for large twist angles. During twisting the kink motion is jerky and uncorrelated at small twist angles. The probability density function (PDF) of jerks strength follows approximately a Gaussian distribution, indicating a mild deformation mode. The kink dynamics transforms from mild to wild at larger twist angles when complex twin patterns with a high density of junctions are generated. The collective motion of kinks now shows avalanche behavior with the energy being power-law distributed. The wildness, which measures the proportion of strain energy relaxed through such avalanches, is correlated with the junction density, and controlled by the external length scale (wire diameter) as well as an internal length scale (twin boundary spacing). Good strain-stress recoverability is achieved when unloading the wire before the formation of complex twin patterns. We correlate the evolution of twin patterns with a statistical analysis of jerk dynamics, which identifies the unique mechanical properties governed by twin boundary motion in nanowires.

 

 

ACTA Vol. 195, 15 Aug. 2020, P59-70

Effects of heat treatment and build orientation on the evolution of ϵ and α′ martensite and strength during compressive loading of additively manufactured 304L stainless steel

增材制造304L不锈钢热处理及打印方向对ϵ和α′组织演变和压缩性能的影响

摘要

        作者研究了热处理和打印方向对增材制造304L不锈钢中马氏体相变的影响，并与常规锻造材料进行了比较。通过实验观测建立了材料组织与马氏体相变和力学性能之间的联系。通过高能X射线粉末衍射原位观测了压缩过程中ϵ 和α′马氏体的演化过程。使用背散电子衍射研究了初始组织的晶粒形貌，取向和织构。可通过热处理对增材制造样品的组织进行调控，不同的组织在压缩过程中的马氏体相变也不同。1100℃以下，马氏体相变比例随着热处理温度升高而降低；1100℃以上，由于再结晶的影响，导致马氏体相变比例随着热处理温度升高而升高。同时实验还观测到，当压缩方向平行于打印方向时（相比于垂直情况），应力诱导马氏体相变比例降低。这是由于在后者的加载条件下，晶粒取向的有利分布促进了马氏体相变。以上结果以及EBSD对晶粒尺寸，取向差等方面的实验观测均表明，使用增材制造方法制备的金属材料的显微组织对其力学性能有显著的影响。

英文摘要

The effect of heat-treatment and build orientation on martensitic phase transformation in additively manufactured (AM) 304L stainless steel is studied and compared with conventionally produced wrought material. The relationships between observed martensitic transformations and material microstructures and their effects on mechanical strength are established through experimental observations. In situ high-energy X-ray powder diffraction measurements were performed to monitor the evolution of ϵ and α′ martensite during compressive loading of stainless steel. Electron backscatter diffraction (EBSD) was used to provide insight on initial grain morphology, crystallographic misorientation within grains, and crystallographic texture. Heat treatment alters the microstructure of AM samples creating different initial conditions. This difference in starting microstructure resulted in variability in martensitic transformation during compressive deformation. The rate of martensitic transformation decreased for AM samples treated with temperatures up to 1100∘C, after which the AM microstructures recrystallized, resulting in increased rate of martensitic transformation for those samples treated at higher temperatures. It was also observed that aligning the axis of compression with the AM build direction resulted in a lower rate of strain-induced martensite formation as opposed to aligning the compression axis perpendicular to it. More favorable distribution of crystal orientations in the latter loading orientation promoted martensitic transformation. These and additional experimental observations from EBSD in terms of kernel average misorientation, mean grain orientation spread, and mean crystallite size reveal strong microstructural effects on strength of additively manufactured metallic materials.

 

 

ACTA Vol. 195, 15 Aug. 2020, P71-80

Consideration of kinetics on intermetallics formation in solid-solution high entropy alloys

固溶态高熵合金中的金属间化合物形成动力学

 

 

摘要

        已有大量的实验观测表明，高熵合金在中温区可生成金属间化合物在。在本研究中，作者提出了一种模型，用于描述动力学对热力学上可形成析出相的干预作用。这一模型很好地解释了文献中普遍观察到的高熵合金在中温范围内有金属间化合物形成的现象。为了进一步阐明动力学的影响，作者选择了等原子比的CrMnFeCoNi合金，即Cantor合金作为研究材料，使用DSC技术研究不同加热速率下合金中的金属间化合物形成情况。研究发现，在200℃-900℃区间内，有四种金属间化合物可能析出，分别是BCC-Cr, L10-NiMn, B2-FeCo 和富Cr 的σ相。而在900℃以上，合金为完全固溶态。基于DSC测量结果，研究者绘制了Cantor 合金的准平衡TTT 图，这也是首次在高熵合金中成功绘制TTT图。

英文摘要

There are overwhelming experimental observations indicating intermetallic (IM) phase formed in the intermediate temperatures in high entropy alloys. In this study, we proposed a model to show how kinetics could intervene the thermodynamic determination of phase formation. The model offers a good explanation for the prevalent formation of IM formation in the intermediate temperature range in high entropy alloys available in the literature. To further demonstrate the kinetic effect, we selected the equiatomic CrMnFeCoNi alloy (i.e., Cantor Alloy) as a surrogate material and employed differential scanning calorimetry (DSC) at different heating rates to investigate IM formation in this alloy. In this case, we found the presence of four IM compounds, BCC-Cr, L10-NiMn, B2-FeCo, and Cr-rich σ phases, in the temperature ranging from about 200 to 900°C, above which the alloy was a complete solid solution. From the DSC measurements, we were also able to build a quasi-equilibrium TTT diagram for Cantor Alloy. It was the first time that such a TTT diagram was established for a high entropy alloy.

 

 

ACTA Vol. 195, 15 Aug. 2020, P81-86

Composition dependence of metallic glass plasticity and its prediction from anelastic relaxation – A shear transformation zone analysis

金属玻璃塑性的成分依赖以及基于非弹性弛豫的塑性预测——切变区分析

 

摘要

        金属玻璃的力学弛豫行为对成分是十分敏感的。例如在动态力学分析中，La70Ni15Al15在高频和/或低温下存在一个明显的归一化损耗模量的二次峰，称为β弛豫；而La70Cu15Al15只有一个峰。作者通过准静态滞弹性弛豫测量，确定了这些合金在室温下超过11个量级时间范围内的弛豫-时间谱，用于描述α和β两种模态下的切变区域（STZ）的特性。与La70Cu15Al15相比，La70Ni15Al15合金中显著的β弛豫峰是由于大量快而小的切变区域和少量慢而大的切变区域共同导致的。室温拉伸试验表明材料的塑性随应变率的降低而提高，具有热激活过程的特征。La70Cu15Al15比La70Ni15Al15表现出更好的塑性，这种塑性与β弛豫强度之间的负相关关系与前人的研究结果相反。鉴于STZ谱常被用于解释两种合金的塑性差异，学界需要对损耗模量进行更加精确的测量，并且对基于这类测量结果进行的塑性预测进行修正。

英文摘要

The mechanical relaxation behavior of metallic glasses (MGs) is composition sensitive. For example, in dynamic mechanical analysis, La70Ni15Al15 shows a pronounced secondary peak, termed β relaxation, of the normalized loss modulus at high frequency and/or low temperature, while La70Cu15Al15 only exhibits a shoulder. We have determined relaxation-time spectra at room temperature for these alloys over eleven orders of magnitude of time from quasi-static anelastic relaxation measurements. These are employed to characterize shear transformation zone (STZ) properties in both the α and β regimes. The pronounced β relaxation peak, observed for La70Ni15Al15, is a result of both larger volume fraction of fast and small potential STZs and smaller volume fraction of slow and large potential STZs as compared to La70Cu15Al15. Room-temperature tensile tests show increasing plasticity with decreasing strain rates, characteristic of thermally activated processes. La70Cu15Al15 exhibits greater plasticity than La70Ni15Al15, a negative correlation with the intensity of the β relaxation that is opposite to that previously suggested. The STZ spectra are used to explain the plasticity difference between the two alloys. Plasticity predictions from loss modulus measurements need to be revised, and require absolute measurements.

 

 

ACTA Vol. 195, 15 Aug. 2020, P87-97

Radius-dependent homogeneous strain in uncoalesced GaN nanowires

非聚合GaN纳米线的径向相关均匀应变

 

摘要

         作者研究了通过等离子体辅助分子束外延技术，在Ti/Al2O3(0001)衬底上制备的低厚度、（几乎）无聚合的自组装GaN纳米线体系的应变状态。高分辨率X射线衍射中布拉格峰的偏移表明，在指向平面外方向存在均匀的拉伸应变。该应变与纳米线的平均半径成反比，由作用于纳米线侧壁的表面应力引起。不同半径的纳米线的应变叠加导致了在宏观尺度上类似非均匀应变的布拉格峰展宽。纳米线体系在光致发光光谱中出现了束缚激子跃迁的少量蓝移，反映了平面内的补偿压缩应变。掠入射状态下的同步辐射XRD测量结果进一步支持了这一观点。结合X射线衍射和光致发光光谱结果，可知构成纳米线侧壁的裸露氮化镓平面的表面应力分量fx和fz分别为2.25和-0.7 N/m。

英文摘要

We investigate the strain state of ensembles of thin and nearly coalescence-free self-assembled GaN nanowires prepared by plasma-assisted molecular beam epitaxy on Ti/Al2O3(0001) substrates. The shifts of Bragg peaks in high-resolution X-ray diffraction profiles reveal the presence of a homogeneous tensile strain in the out-of-plane direction. This strain is inversely proportional to the average nanowire radius and results from the surface stress acting on the nanowire sidewalls. The superposition of strain from nanowires with different radii in the same ensemble results in a broadening of the Bragg peaks that mimics an inhomogeneous strain on a macroscopic scale. The nanowire ensembles show a small blueshift of the bound-exciton transitions in photoluminescence spectra, reflecting the existence of a compensating in-plane compressive strain, as further supported by grazing incidence x-ray diffraction measurements carried out at a synchrotron. By combining X-ray diffraction and photoluminescence spectroscopy, the surface stress components fx and fz of the air-exposed GaN planes that constitute the nanowire sidewalls are determined experimentally to be 2.25 and -0.7 N/m, respectively.



 

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