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金屬頂刊雙語導讀丨Acta Mater. Vol.195

2020-06-09 來源：Goal Science

        《Acta Materialia》本期（Volume 195, 15 August 2020）刊出9篇科研論文，涵蓋高熵合金、鋁銅合金、鎂合金以及不銹鋼等多個金屬材料領域。

 

Vol. 195 目錄

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

集成三維微觀尺度分析揭示第二相粒子對晶粒異常長大影響的動力學特征

 

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

鎂{10-12}孿晶中形成位錯需要滿足的動力學和能量要求

 

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

長周期有序堆垛Mg-Zn-Y合金中的扭折形成過程

 

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

擴散、缺陷以及含鉑B2 NiAl涂層與單晶高溫合金間多組分互擴散區的長大

 

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

孿晶 α-Fe 納米線在扭轉過程中從溫和到劇烈的動力學“雪崩”

 

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

增材制造304L不銹鋼熱處理及打印方向對?和α′組織演變和壓縮性能的影響

 

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

固溶態高熵合金中的金屬間化合物形成動力學

 

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

金屬玻璃塑性的成分依賴以及基于非彈性弛豫的塑性預測——切變區分析

 

9. Radius-dependent homogeneous strain in uncoalesced GaN nanowires

非聚合GaN納米線的徑向相關均勻應變

 

 

ACTA Vol. 195, 15 Aug. 2020, P1-12

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

集成三維微觀尺度分析揭示第二相粒子對晶粒異常長大影響的動力學特征

 

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

        通常彌散分布在金屬、陶瓷等多晶體材料中的第二相粒子會阻礙晶粒長大，使晶粒細化，提升材料的力學性能。然而，在較高溫度下經常會觀測到部分晶粒的優先長大或異常長大，使得材料的使用壽命大大降低。第二相粒子促進晶粒異常長大的成因和機理一直是學界爭論的焦點。在本研究中，作者通過3D-XRD成像技術，揭示了Al-Cu模型合金中晶界和第二相粒子之間的復雜交互作用。在具有高度非隨機分布粒子的體系中，觀測到了晶粒的異常長大現象。初始晶粒尺寸受控于第二相粒子的集中分布情況，大晶粒往往產生在第二相粒子較少的區域，而某些特定尺寸的晶粒可能會“逃離”晶粒尺寸分布，與考慮了表面張力和粒子釘扎的理論模型預測結果一致。

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

鎂{10-12}孿晶中形成位錯需要滿足的動力學和能量要求

 

 

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

        根據已發表文獻中關于密排六方金屬中基體位錯和{10-12}孿晶界相互作用的TEM和分子動力學研究結果，啟發學界作出了如下猜想，即在孿晶中可以形成 柏氏矢量的位錯。目前已有報道稱，當基體中的基底位錯被前進中的孿晶界掃過時，它們會轉化為孿晶基底 I1層錯上的分位錯。在本研究中我們發現，從能量的角度而言，孿晶界附近的一對分位錯在有在孿晶內形成一個 位錯的傾向。原位TEM觀測結果證實了這一假設，發現長位錯偶極子的一端終止于孿晶界，另一端終止于I1 層錯。產生的近似螺位錯的位錯偶極子是可滑動的，在某些情況下能夠自我湮滅。因此，相較于利用一個高能量位錯堆垛把兩個位錯通過一個孿晶界壓成一個位錯，位錯更傾向于在孿晶界向基體內部遷移的過程中，在Mg的{10-12}孿晶中自發形成。這些觀測結果有助于解釋孿晶自身的后續變形，以及為什么它們在在塑性剪切應力集中的情況下特別容易表現出較大的脆性。

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

長周期有序堆垛Mg-Zn-Y合金中的扭折形成過程

 

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

擴散、缺陷以及含鉑B2 NiAl涂層與單晶高溫合金間多組分互擴散區的長大

 

摘要

        在四元非均勻體系的條件下求解Onsager理論的相關方程是極其困難的，因此本研究采用了偽二元和偽三元擴散偶方法實驗測定了B2-Ni(CoPt)Al體系中與組分有關的擴散系數，基于熱力學選擇合適的端元組分形成理想/近似理想的擴散分布。在有Co元素存在的情況下，Ni和Al的偽二元互擴散系數降低；而在有Pt元素存在的情況下，Ni和Al的偽二元互擴散系數增加。偽三元互擴散系數實驗表明，在有Pt元素存在的條件下，主要的互擴散系數顯著增加。同時交叉互擴散系數的變化較小，印證了組分間擴散相互作用的微小變化。與互擴散系數的變化相比，成分相關的熱力學驅動力則表現出相反的趨勢，Pt(Co)誘導的點缺陷濃度的改變可能起到主要作用。第一性原理計算表明，Pt的添加使Ni元素的空位濃度增加，降低了三重缺陷擴散機制的活化能。這些發現可以用于解釋添加Pt元素導致B2-Ni(Pt)Al涂層和Rene N5單晶高溫合金之間互擴散區厚度增加的現象。此外，EPMA和TEM分析揭示了富難熔元素的析出物長大過程。

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

孿晶 α-Fe 納米線在扭轉過程中從溫和到劇烈的動力學“雪崩”

 

摘要

        本研究利用分子動力學模擬了帶有孿晶界的α-鐵納米線的扭轉行為。扭轉納米線將導致孿晶璧上產生拓撲缺陷。當扭轉角較小時，孿晶壁內會產生扭折扭折; 當扭轉角較大時，會進一步在扭折之間形成結節。在扭轉過程中，小扭轉角條件下，扭折的運動表現為抽動且互不相關。抽動強度的概率密度函數近似為高斯分布，表現為一種“溫和”的變形模式。當扭轉角增大時，由于具有高密度結節的復雜孿晶模式的產生，扭折的動力學模式從溫和變為劇烈。扭折的集體運動行為類似雪崩，其能量遵循冪律分布。劇烈程度可以通過在雪崩似的運動中應變能的釋放比例進行描述，它與結節密度密切相關，并且同時受到外部長度范圍（即納米線直徑）和內部長度范圍（即孿晶界間距）的控制。在形成復雜孿晶之前卸載可使納米線獲得良好的應變-應力恢復能力。本研究將孿晶模式的演變與抽動過程的動力學統計分析聯系起來，從而確定了納米線中由孿晶邊界運動所控制的獨特力學特性。

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 ? and α′ martensite and strength during compressive loading of additively manufactured 304L stainless steel

增材制造304L不銹鋼熱處理及打印方向對?和α′組織演變和壓縮性能的影響

摘要

        作者研究了熱處理和打印方向對增材制造304L不銹鋼中馬氏體相變的影響，并與常規鍛造材料進行了比較。通過實驗觀測建立了材料組織與馬氏體相變和力學性能之間的聯系。通過高能X射線粉末衍射原位觀測了壓縮過程中? 和α′馬氏體的演化過程。使用背散電子衍射研究了初始組織的晶粒形貌，取向和織構。可通過熱處理對增材制造樣品的組織進行調控，不同的組織在壓縮過程中的馬氏體相變也不同。1100℃以下，馬氏體相變比例隨著熱處理溫度升高而降低；1100℃以上，由于再結晶的影響，導致馬氏體相變比例隨著熱處理溫度升高而升高。同時實驗還觀測到，當壓縮方向平行于打印方向時（相比于垂直情況），應力誘導馬氏體相變比例降低。這是由于在后者的加載條件下，晶粒取向的有利分布促進了馬氏體相變。以上結果以及EBSD對晶粒尺寸，取向差等方面的實驗觀測均表明，使用增材制造方法制備的金屬材料的顯微組織對其力學性能有顯著的影響。

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 ? 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

固溶態高熵合金中的金屬間化合物形成動力學

 

 

摘要

        已有大量的實驗觀測表明，高熵合金在中溫區可生成金屬間化合物在。在本研究中，作者提出了一種模型，用于描述動力學對熱力學上可形成析出相的干預作用。這一模型很好地解釋了文獻中普遍觀察到的高熵合金在中溫范圍內有金屬間化合物形成的現象。為了進一步闡明動力學的影響，作者選擇了等原子比的CrMnFeCoNi合金，即Cantor合金作為研究材料，使用DSC技術研究不同加熱速率下合金中的金屬間化合物形成情況。研究發現，在200℃-900℃區間內，有四種金屬間化合物可能析出，分別是BCC-Cr, L10-NiMn, B2-FeCo 和富Cr 的σ相。而在900℃以上，合金為完全固溶態。基于DSC測量結果，研究者繪制了Cantor 合金的準平衡TTT 圖，這也是首次在高熵合金中成功繪制TTT圖。

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

金屬玻璃塑性的成分依賴以及基于非彈性弛豫的塑性預測——切變區分析

 

摘要

        金屬玻璃的力學弛豫行為對成分是十分敏感的。例如在動態力學分析中，La70Ni15Al15在高頻和/或低溫下存在一個明顯的歸一化損耗模量的二次峰，稱為β弛豫；而La70Cu15Al15只有一個峰。作者通過準靜態滯彈性弛豫測量，確定了這些合金在室溫下超過11個量級時間范圍內的弛豫-時間譜，用于描述α和β兩種模態下的切變區域（STZ）的特性。與La70Cu15Al15相比，La70Ni15Al15合金中顯著的β弛豫峰是由于大量快而小的切變區域和少量慢而大的切變區域共同導致的。室溫拉伸試驗表明材料的塑性隨應變率的降低而提高，具有熱激活過程的特征。La70Cu15Al15比La70Ni15Al15表現出更好的塑性，這種塑性與β弛豫強度之間的負相關關系與前人的研究結果相反。鑒于STZ譜常被用于解釋兩種合金的塑性差異，學界需要對損耗模量進行更加精確的測量，并且對基于這類測量結果進行的塑性預測進行修正。

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納米線的徑向相關均勻應變

 

摘要

         作者研究了通過等離子體輔助分子束外延技術，在Ti/Al2O3(0001)襯底上制備的低厚度、（幾乎）無聚合的自組裝GaN納米線體系的應變狀態。高分辨率X射線衍射中布拉格峰的偏移表明，在指向平面外方向存在均勻的拉伸應變。該應變與納米線的平均半徑成反比，由作用于納米線側壁的表面應力引起。不同半徑的納米線的應變疊加導致了在宏觀尺度上類似非均勻應變的布拉格峰展寬。納米線體系在光致發光光譜中出現了束縛激子躍遷的少量藍移，反映了平面內的補償壓縮應變。掠入射狀態下的同步輻射XRD測量結果進一步支持了這一觀點。結合X射線衍射和光致發光光譜結果，可知構成納米線側壁的裸露氮化鎵平面的表面應力分量fx和fz分別為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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