Materials Characterization最新文献_第2页

Long-term thermal aging effects in ferritic-martensitic steel HT9 铁素体-马氏体钢 HT9 的长期热老化效应

IF 4.8 2区材料科学 Q1 MATERIALS SCIENCE, CHARACTERIZATION & TESTING

Materials Characterization

Pub Date : 2024-09-30 DOI: 10.1016/j.matchar.2024.114418

The ferritic-martensitic steel HT9 is a candidate material for fuel cladding and core components in advanced nuclear reactors, such as sodium-cooled fast reactors, thanks to their high temperature mechanical properties and low susceptibility to irradiation induced swelling phenomena. However, thermal stability and elevated temperature microstructural evolution in these alloys may impact their long-term behavior and reliability. In this work, the effects of thermal aging on the microstructural and mechanical properties of HT9 have been investigated through complementary electron microscopy, synchrotron X-ray diffraction, microhardness, and thermodynamic modeling. Plates of HT9 were aged up to 50 kh at relevant sodium-cooled fast reactor operational temperatures (360 °C - 700 °C). Trends in microstructure as a function of aging time and temperature were apparent from qualitative and quantitative analysis. These observations were further supported by thermodynamic modeling of the bulk and precipitate phases. Specific phases observed include BCC Fe, FCC M₂₃C₆, HCP and FCC MX phase and Laves M₂X phase. Through the application of our multi-scale and multi-modal approach, clear information on the aging mechanism of HT9 was obtained, allowing for a more informed prediction, and understanding of the long-term behavior, performance and thermal stability of ferritic-martensitic alloys exposed to elevated temperatures.

铁素体-马氏体钢 HT9 具有高温机械性能，不易受辐照诱导的膨胀现象影响，是钠冷快堆等先进核反应堆燃料包壳和堆芯部件的候选材料。然而，这些合金的热稳定性和高温微结构演变可能会影响其长期性能和可靠性。在这项工作中，通过补充电子显微镜、同步辐射 X 射线衍射、显微硬度和热力学建模，研究了热老化对 HT9 的微观结构和机械性能的影响。在相关的钠冷快堆运行温度（360 °C - 700 °C）下，对 HT9 板材进行了长达 50 kh 的老化。通过定性和定量分析，可以明显看出微观结构随老化时间和温度变化的趋势。这些观察结果得到了块状相和沉淀相热力学模型的进一步支持。观察到的特定相包括 BCC Fe、FCC M23C6、HCP 和 FCC MX 相以及 Laves M2X 相。通过应用我们的多尺度和多模态方法，获得了 HT9 老化机制的明确信息，从而可以对暴露在高温下的铁素体-马氏体合金的长期行为、性能和热稳定性进行更明智的预测和理解。

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引用次数: 0

Microstructure and mechanical property of Zr-3/CoCrFeMnNi high-entropy alloys joints brazed using a novel ZrCu alloys 使用新型 ZrCu 合金钎焊的 Zr-3/CoCrFeMnNi 高熵合金接头的显微结构和机械性能

IF 4.8 2区材料科学 Q1 MATERIALS SCIENCE, CHARACTERIZATION & TESTING

Materials Characterization

Pub Date : 2024-09-29 DOI: 10.1016/j.matchar.2024.114411

In this paper, the Zr53Cu47 (wt%) alloys were designed by vacuum melting for the joining Zirconium (Zr) alloys to equiatomic CoCrFeMnNi high entropy alloys (HEA). The wetting, microstructure, growth kinetics of reaction layer, shear strength and rupture behavior of joints evolved with temperature were specifically deliberated. The interfacial reactions were determined to be CrMn layer/Zr(Cr,Mn)₂ layer + corpuscular β-Zr/tuberous Zr₂(Cu,Ni,Co,Fe) + Zrss + tuberous Zr(Cr,Mn)₂ from HEA to Zr-3. Herein, the β-Zr precipitates with the sterling plasticity had the semi-coherent relationship with the matrix phase Zr(Cr,Mn)₂, and β-Zr precipitates developed with the elevated temperature, contributing to the plasticity improvement of Zr(Cr,Mn)₂ and the growth of joints properties. The activation energy (Q) of CrMn was 127.0 kJ/mol, significantly less than that that of Zr(Cr,Mn)₂ (159.7 kJ/mol), thereby the generation of CrMn was underlying to Zr(Cr,Mn)₂ during brazing. Moreover, grains orientations in CrMn and Zr(Cr,Mn)₂ were stochastically dispersed. The strength of Zr-3/Zr53Cu47/HEA achieved peak of 136.8 MPa when brazed at 970 °C/10 min. Cracks were preferably started at the non-coherent interface of Zr(Cr,Mn)₂/CrMn with the higher lattice mismatch degree of 26.0 % in I area, and propagated toward tuberous Zr₂(Cu,Ni,Co,Fe) in II area.

本文采用真空熔炼法设计了 Zr53Cu47 (wt%) 合金，用于连接锆 (Zr) 合金和等原子 CoCrFeMnNi 高熵合金 (HEA)。具体研究了湿润、微观结构、反应层生长动力学、剪切强度以及接头随温度变化的断裂行为。确定了从 HEA 到 Zr-3 的界面反应为 CrMn 层/Zr(Cr,Mn)2 层 + 团状 β-Zr/ 团状 Zr2(Cu,Ni,Co,Fe)+Zrss+团状 Zr(Cr,Mn)2。其中，具有立体塑性的β-Zr析出物与基体相Zr(Cr,Mn)2具有半相干性，β-Zr析出物随温度升高而发展，促进了Zr(Cr,Mn)2塑性的改善和接头性能的增长。铬锰的活化能（Q）为 127.0 kJ/mol，明显低于 Zr（Cr,Mn）2 的活化能（159.7 kJ/mol），因此在钎焊过程中，铬锰的生成是 Zr（Cr,Mn）2 的基础。此外，CrMn 和 Zr(Cr,Mn)2 的晶粒取向是随机分散的。在 970 °C/10 分钟的钎焊温度下，Zr-3/Zr53Cu47/HEA 的强度达到 136.8 兆帕的峰值。裂纹最好从晶格失配度较高的 Zr(Cr,Mn)2/CrMn（I 区）的非相干界面（26.0%）开始，并向 II 区的块状 Zr2(Cu,Ni,Co,Fe)扩展。

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引用次数: 0

Microstructure evolution mechanism of WB-doped Fe-based amorphous composite coating under proton beam irradiation 质子束辐照下 WB 掺杂铁基非晶复合涂层的微观结构演化机理

IF 4.8 2区材料科学 Q1 MATERIALS SCIENCE, CHARACTERIZATION & TESTING

Materials Characterization

Pub Date : 2024-09-27 DOI: 10.1016/j.matchar.2024.114414

Fe-based amorphous coatings exhibit exceptional irradiation resistance attributed to their distinct topologically disordered structure, rendering them highly attractive for advanced nuclear energy applications. The incorporation of WB secondary phase doping can notably alter the coating to enhance its operational safety. In this investigation, three different Fe-based composite coatings, with varying WB doping levels of 5 %, 10 %, and 15 % were fabricated through the High-Velocity Oxy-Fuel (HVOF) spraying technique. Irradiation tests were conducted at room temperature utilizing a proton beam with an energy of 1.52 MeV to simulate neutron irradiation environment in a nuclear reactor. The microstructure evolution before and after irradiation was systematically investigated with XRD, SEM, and TEM techniques. The results demonstrated that proton irradiation induced free volume, crystallization and H bubbles evolution. The doping of WB diminished the proton implantation dose threshold for segregation in irradiation plateaus while enhancing the growth of precipitates around the damage zone by inducing the production of M₂₃C₆ carbides and, at the same time, increasing the probability of H bubble nucleation and growth. These findings provide insights for iterative updates in Fe-based amorphous materials, informing their further development and application.

铁基无定形涂层因其独特的拓扑无序结构而表现出卓越的耐辐照性能，使其在先进核能应用中具有极高的吸引力。加入 WB 二相掺杂可以显著改变涂层，从而提高其运行安全性。在这项研究中，通过高速富氧燃料（HVOF）喷涂技术制造了三种不同的铁基复合涂层，其 WB 掺杂水平分别为 5%、10% 和 15%。利用能量为 1.52 MeV 的质子束在室温下进行了辐照试验，以模拟核反应堆中的中子辐照环境。利用 XRD、SEM 和 TEM 技术对辐照前后的微观结构演变进行了系统研究。结果表明，质子辐照诱导了自由体积、结晶和 H 气泡的演化。WB 的掺杂降低了辐照高原偏析的质子植入剂量阈值，同时通过诱导 M23C6 碳化物的产生，促进了损伤区周围沉淀物的生长，同时增加了 H 气泡成核和生长的概率。这些发现为铁基非晶材料的迭代更新提供了启示，为其进一步开发和应用提供了参考。

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引用次数: 0

Microstructure and property evolution of CuCr50 alloy prepared by aluminum thermal reduction-electromagnetic casting during hot forging process 铝热还原-电磁铸造制备的 CuCr50 合金在热锻过程中的显微组织和性能演变

IF 4.8 2区材料科学 Q1 MATERIALS SCIENCE, CHARACTERIZATION & TESTING

Materials Characterization

Pub Date : 2024-09-27 DOI: 10.1016/j.matchar.2024.114400

To address the problems of low performance and density in CuCr50 alloys prepared by aluminum thermal reduction-electromagnetic casting, a synergistic process involving hot forging deformation to eliminate micropores in the alloy and heat treatment to modify the alloy was proposed. The effect of hot forging temperature on the microstructure evolution and performance strengthening of CuCr50 alloys during heat treatment was studied. The results show that the properties of CuCr50 alloys forged at different temperatures after heat treatment are better than those after direct heat treatment. After heat treatment, the conductivity of CuCr50 alloys forged at 800 °C reaches 22.41 MS/m, the density reaches 7.94 g/cm³, and the hardness reaches 112 HB, which are 73.59 %, 4.75 % and 37.59 % greater than those of the as-cast alloy, respectively. The microstructure analysis showed that the nano-Cr phase precipitated during the aging process of CuCr50 alloys after hot forging at 750 °C–850 °C had a semi-coherent relationship with the Cu matrix, which played a role in coherent strengthening. After hot forging at 900 °C, the precipitated Cr phase has an incoherent relationship with the Cu matrix, which played a role of dispersion strengthening. The performance test of 40.5 kV simulated vacuum interrupter shows that the breaking and chopping performance of the prepared CuCr50 contact material is obviously better than that of commercial products, which is expected to become a new process for the preparation of high performance CuCr contact materials.

为解决铝热还原-电磁铸造制备的 CuCr50 合金的低性能和低密度问题，提出了一种协同工艺，即通过热锻变形消除合金中的微孔，并通过热处理对合金进行改性。研究了热锻温度对热处理过程中 CuCr50 合金微观结构演变和性能强化的影响。结果表明，不同温度下锻造的 CuCr50 合金经热处理后的性能优于直接热处理后的性能。热处理后，800 ℃锻造的 CuCr50 合金的电导率达到 22.41 MS/m，密度达到 7.94 g/cm3，硬度达到 112 HB，分别比铸造时的合金高 73.59 %、4.75 % 和 37.59 %。显微组织分析表明，750 ℃-850 ℃热锻后的 CuCr50 合金在时效过程中析出的纳米铬相与铜基体呈半相干关系，起到了相干强化的作用。在 900 ℃ 热锻后，析出的铬相与铜基体呈非相干关系，起到了分散强化的作用。40.5 kV 模拟真空灭弧室性能测试表明，制备的 CuCr50 触头材料的断裂和劈裂性能明显优于商用产品，有望成为制备高性能 CuCr 触头材料的新工艺。

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引用次数: 0

Laves phase control and tensile properties optimization of DED-arc repaired 718Plus components through the addition of TiC and Cr2C3 通过添加 TiC 和 Cr2C3 实现电弧放电修复 718Plus 部件的 Laves 相控制和拉伸性能优化

IF 4.8 2区材料科学 Q1 MATERIALS SCIENCE, CHARACTERIZATION & TESTING

Materials Characterization

Pub Date : 2024-09-27 DOI: 10.1016/j.matchar.2024.114415

Directed energy deposition-arc (DED-arc) additive manufacturing technology was used to repair the damaged 718Plus components. This work shows that TiC/Cr₂C₃ addition to 718Plus alloy is an effective way to suppress the formation of the unfavorable Laves phase. TiC additions to 718Plus alloy can alleviate the elemental segregation, refine the dendritic structure and promote the formation of blocky TiC-NbC core-shell carbides and NbC carbides, while Cr₂C₃ additions enable the precipitation of rod-like NbC carbides. During the deposition process, the TiC/Cr₂C₃ additions were dissolved into the molten pool and decomposed into Ti, Cr, and C. The introduction of additional carbon in the melt drastically consumed the Nb available for Laves phase. The tensile tests show that TiC addition to 718Plus alloy contributed to an increased tensile strength of about 120 MPa due to the reduced amount of Laves phase and the reinforced effect of carbides. The fracture behaviour of carbides was explained in detail. The critical shear stress for blocky carbides to crack is higher than that required for rod-like ones, suggesting that TiC additions were desirable for better ductility compared with Cr₂C₃ additions.

定向能沉积电弧（DED-arc）快速成型技术用于修复受损的 718Plus 组件。这项研究表明，在 718Plus 合金中添加 TiC/Cr2C3 是抑制不利拉维斯相形成的有效方法。在 718Plus 合金中添加 TiC 可减轻元素偏析、细化树枝状结构并促进块状 TiC-NbC 核壳碳化物和 NbC 碳化物的形成，而添加 Cr2C3 则可析出棒状 NbC 碳化物。在沉积过程中，TiC/Cr2C3 添加物溶解到熔池中并分解成 Ti、Cr 和 C。拉伸试验表明，在 718Plus 合金中添加 TiC 后，拉伸强度提高了约 120 兆帕，这是由于 Laves 相的数量减少以及碳化物的强化作用。详细解释了碳化物的断裂行为。块状碳化物开裂所需的临界剪切应力高于棒状碳化物，这表明与添加 Cr2C3 相比，添加 TiC 可获得更好的延展性。

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引用次数: 0

Enhancing charpy absorbed energy of aged duplex lightweight steel plates through TRIP and TWIP mechanisms 通过 TRIP 和 TWIP 机制提高时效双相轻质钢板的夏比吸收能

IF 4.8 2区材料科学 Q1 MATERIALS SCIENCE, CHARACTERIZATION & TESTING

Materials Characterization

Pub Date : 2024-09-25 DOI: 10.1016/j.matchar.2024.114413

Ensuring toughness in thick hot-rolled plates remains a challenge for lightweight steels in automotive, shipbuilding, military, and construction industries despite improved tensile properties. This study investigated the Charpy absorbed energy of thick hot-rolled Fe-0.4C-15Mn-6Al duplex lightweight steel plates exhibiting TRIP and TWIP mechanisms, aged at 450–500 °C to precipitate κ-carbides. Fracture initiation and propagation energies measured from instrumented Charpy impact testing were analyzed through microstructural and microfracture analyses. The 500 °C-aged (A500) specimen showed the highest Charpy absorbed energy, composed of the highest fracture initiation and propagation energies across all test temperatures, particularly due to active TWIP and TRIP mechanisms along with significant κ-carbide precipitation strengthening. Despite predominantly ductile fracture modes, regardless of aging temperature and test temperature, deformation mechanisms were influenced by stacking fault energy (SFE). Aging resulted in κ-carbide precipitation, reducing C and Mn contents in austenite and lowering SFE. At 25 °C, the superior energy absorption of the A500 specimen (296 J) was attributed to its high flow stress and extensive roughness in the fracture surface due to crack deflection in the fracture initiation region and zigzag crack propagation. The Charpy absorbed energy decreased significantly at lower temperatures due to limited development of slip line field and less zigzag crack propagation. Despite this, the A500 specimen maintained the highest energy absorption due to its optimized TWIP and TRIP mechanisms and κ-carbide precipitation strengthening.

尽管汽车、造船、军事和建筑行业的轻质钢材的拉伸性能有所改善，但如何确保热轧厚钢板的韧性仍然是一项挑战。本研究调查了在 450-500 °C 下老化以析出κ-碳化物的厚热轧 Fe-0.4C-15Mn-6Al 双相轻质钢板在 TRIP 和 TWIP 机制下的夏比吸收能。通过微观结构和微观断裂分析，对仪器夏比冲击试验测得的断裂起始和扩展能量进行了分析。500 °C 老化（A500）试样显示出最高的夏比吸收能，在所有测试温度下都具有最高的断裂萌发能和扩展能，特别是由于活跃的 TWIP 和 TRIP 机制以及显著的 κ 碳化物沉淀强化。尽管主要是韧性断裂模式，但无论老化温度和测试温度如何，变形机制都受到堆积断层能（SFE）的影响。时效导致κ-碳化物析出，减少了奥氏体中的C和Mn含量，降低了SFE。25 °C时，A500试样的能量吸收较好（296 J），这是因为其流动应力较高，断裂起始区域的裂纹偏转和之字形裂纹扩展导致断裂表面粗糙度较大。在较低温度下，由于滑移线场的发展有限，人字形裂纹扩展较少，夏比吸收能明显下降。尽管如此，由于优化了 TWIP 和 TRIP 机制以及 κ 碳化物沉淀强化，A500 试样仍保持了最高的能量吸收率。

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引用次数: 0

Impact of Hf alloying on the functional properties of Ni-Mn-Ga high temperature shape memory alloys Hf 合金对 Ni-Mn-Ga 高温形状记忆合金功能特性的影响

IF 4.8 2区材料科学 Q1 MATERIALS SCIENCE, CHARACTERIZATION & TESTING

Materials Characterization

Pub Date : 2024-09-24 DOI: 10.1016/j.matchar.2024.114410

The paper reports on the functional properties and microstructure of polycrystalline Ni-Mn-Ga-Hf high temperature shape memory alloys, in which different amounts of Hf up to 4 at.% are added in substitution of Mn and Ga, while the nominal Ni content is kept constant. The increase in the amount of Hf promotes a decrease in the valence electron concentration (e/a), tetragonality (c/a) of the martensitic unit cell, and martensitic transformation temperatures, as well as a significant decrease of the transformation hysteresis. The non-modulated tetragonal martensite, typical of Ni-Mn-Ga high temperature shape memory alloys, is formed in all the alloys studied here, though the alloy with 4 at.% of Hf also contains a small fraction of modulated 14M martensite. Hf addition improves the thermomechanical response of the alloys under compressive stress up to 300 MPa and leads to nearly closed cycles with minimal irrecoverable strain and low hysteresis (8 K) for the alloys with 3 and 4 at.% of Hf. These alloys also demonstrate excellent stability under repetitive thermal cycling and little change upon aging at 870 K. A second phase rich in Hf and Ni starts to precipitate at 1 at.% of Hf addition and its volume fraction experiences an abrupt and progressive increase for higher Hf contents. The structure of the second phase looks like the usual f.c.c. γ phase reported in other Ni-Mn-Ga-based alloys, but it has a double lattice parameter. Two structural models based on the A6 face-centered tetragonal unit cell with space group I4/mmm (No. 139), equivalent to the double f.c.c. lattice, are proposed for this new phase.

本文报告了多晶镍-锰-镓-铪高温形状记忆合金的功能特性和微观结构，其中在保持标称镍含量不变的情况下，加入了不同含量的铪（最高达 4%）以替代锰和镓。Hf 含量的增加促进了价电子浓度（e/a）、马氏体单元的四方性（c/a）和马氏体转变温度的降低，并显著减少了转变滞后。本文研究的所有合金都形成了非调制四方马氏体，这是典型的镍-锰-镓高温形状记忆合金，但含 4% Hf 的合金也含有一小部分调制 14M 马氏体。添加铪后，合金在高达 300 兆帕的压缩应力下的热机械响应得到改善，并且在含 3% 和 4% 铪的合金中，几乎实现了封闭循环，不可恢复应变最小，滞后（8 K）较低。这些合金在重复热循环下也表现出极佳的稳定性，在 870 K 下老化时几乎没有变化。当 Hf 含量为 1%时，富含 Hf 和 Ni 的第二相开始析出，随着 Hf 含量的增加，其体积分数突然逐渐增加。第二相的结构类似于其他镍锰镓基合金中常见的 f.c.c. γ 相，但它具有双晶格参数。针对这一新相，提出了两种基于空间群为 I4/mmm（编号 139）的 A6 面心四边形单胞（相当于双 f.c.c. 晶格）的结构模型。

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引用次数: 0

Microstructure characterization of plasma electrolytic oxidation coating on Hf-Nb-Ta-Zr high entropy alloy Hf-Nb-Ta-Zr 高熵合金等离子电解氧化涂层的微观结构表征

IF 4.8 2区材料科学 Q1 MATERIALS SCIENCE, CHARACTERIZATION & TESTING

Materials Characterization

Pub Date : 2024-09-24 DOI: 10.1016/j.matchar.2024.114403

The morphology, composition, and microstructure of plasma electrolytic oxidation (PEO) coating on Hf-Nb-Ta-Zr high entropy alloy (HEA) were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, glow discharge optical emission spectroscopy (GDOES) and transmission electron microscopy (TEM). The formation mechanism of PEO coating was analyzed. It was found that a dense PEO coating of ∼4 μm thick on the HEA surface was formed, which consisted of tetragonal and monoclinic ZrO₂ phases, tetragonal and monoclinic HfO₂ phases, Nb₂O₅ and Ta₂O₅ phases. The PEO coating from the alloy substrate to the surface contained five distinctive layers: amorphous barrier layer, nanocrystalline layer, columnar grain layer, amorphous outer layer, and top porous layer. Their formation was ascribed to the different cooling rates of the melt in the different depths of the discharge channel across the coating. Meanwhile, the formation of an amorphous barrier layer near the HEA substrate was also related to the mutual migration and diffusion of Hf⁴⁺, Nb⁵⁺, Ta⁵⁺, Zr⁴⁺ and O²⁻ besides the rapid cooling of melt in the bottom of the discharge channel. The columnar grains of ∼70 nm wide were mainly composed of the monoclinic ZrO₂ and monoclinic HfO₂ phases, but both the amorphous layers enrich the Ta and Nb elements. It was believed that the high-content Ta and Nb in the HEA enhanced the formation of the amorphous layers.

采用扫描电子显微镜（SEM）、X射线光电子能谱（XPS）、X射线衍射（XRD）、拉曼光谱、辉光放电光发射光谱（GDOES）和透射电子显微镜（TEM）对Hf-Nb-Ta-Zr高熵合金（HEA）上等离子体电解氧化（PEO）涂层的形貌、成分和微观结构进行了表征。分析了 PEO 涂层的形成机理。研究发现，在 HEA 表面形成了厚度为 4 μm 的致密 PEO 涂层，由四方和单斜 ZrO2 相、四方和单斜 HfO2 相、Nb2O5 和 Ta2O5 相组成。从合金基体到表面的 PEO 涂层包含五个不同的层，即非晶阻挡层、纳米晶层、柱状晶粒层、非晶外层和顶部多孔层。它们的形成是由于熔体在涂层上不同深度的放电通道中的冷却速度不同。同时，HEA 基底附近非晶阻挡层的形成除了与放电通道底部熔体的快速冷却有关外，还与 Hf4+、Nb5+、Ta5+、Zr4+ 和 O2- 的相互迁移和扩散有关。宽度为 70 nm 的柱状晶粒主要由单斜 ZrO2 和单斜 HfO2 相组成，但非晶层中都富含 Ta 和 Nb 元素。据认为，HEA 中的高含量 Ta 和 Nb 促进了非晶层的形成。

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引用次数: 0

Molten salt-assisted controlled synthesis of two-dimensional molybdenum carbide 熔盐辅助控制合成二维碳化钼

IF 4.8 2区材料科学 Q1 MATERIALS SCIENCE, CHARACTERIZATION & TESTING

Materials Characterization

Pub Date : 2024-09-24 DOI: 10.1016/j.matchar.2024.114412

The present investigation examines the carbothermal reduction synthesis of two-dimensional molybdenum carbide (2D Mo₂C) using sodium carbonate (Na₂CO₃) as a molten salt diffusion promoter and sodium sulfide (Na₂S) as a solid-state intercalation agent. Raw molybdenum disulfide (MoS₂) powder undergoes carbothermal reduction facilitated by activated carbon and Na₂CO₃ above 800 °C to produce 2D Mo₂C layers intercalated by Na₂S. The diffusion of Na₂S can be enhanced by the fluidity of molten salt Na₂CO₃, leading to the expansion of the Mo₂C layer spacing to 29 nm under the influence of the temperature field. Na₂S intercalation prevents layer shrinkage during cooling while molten Na₂CO₃ directs 2D growth, yielding 10 nm-thick sheets. The product maintains hexagonal β-Mo₂C structure up to 950 °C with microflowers of accordion-shaped nanosheets. Ultrasonication exfoliates the weakly bound Mo₂C layers into uniform, freely suspended flakes around 10–100 nm in lateral size. This work demonstrates the tuning of 2D Mo₂C morphology in high-temperature reactions by utilizing molten salts. The principal results are the synthesis of micrometer-sized Mo₂C sheets with controlled nanoscale thickness and uniform nanosheet dispersions, enabled by molten salt-directed diffusion of intercalated species. The major conclusion drawn is that solid-liquid synergistic diffusion can guide precision synthesis of layered nanomaterials.

本研究采用碳酸钠（Na2CO3）作为熔盐扩散促进剂，硫化钠（Na2S）作为固态插层剂，研究了二维碳化钼（2D Mo2C）的碳热还原合成。原料二硫化钼（MoS2）粉末在 800 °C 以上的温度下，在活性炭和 Na2CO3 的促进下进行碳热还原，生成由 Na2S 插层的二维 Mo2C 层。熔盐 Na2CO3 的流动性可增强 Na2S 的扩散，从而在温度场的影响下将 Mo2C 层间距扩大到 29 nm。Na2S 插层可防止冷却过程中的层收缩，而熔融 Na2CO3 则可引导二维生长，生成 10 纳米厚的薄片。该产品在 950 ℃ 时仍能保持六角形的 β-Mo2C 结构，并带有手风琴状纳米片的微花。超声波将弱结合的 Mo2C 层剥离成横向尺寸约为 10-100 纳米的均匀、自由悬浮的薄片。这项工作展示了利用熔盐在高温反应中调整二维二氯甲烷形态的方法。主要成果是通过熔盐引导的插层物种扩散，合成了具有可控纳米级厚度和均匀纳米片状分散的微米级 Mo2C 片。得出的主要结论是，固液协同扩散可以指导层状纳米材料的精确合成。

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引用次数: 0

CALPHAD-aided design for superior mechanical behavior in Ti40Zr20Hf40-xCrx eutectic refractory high-entropy alloys 通过 CALPHAD 辅助设计实现 Ti40Zr20Hf40-xCrx 共晶耐火高熵合金的卓越机械性能

IF 4.8 2区材料科学 Q1 MATERIALS SCIENCE, CHARACTERIZATION & TESTING

Materials Characterization

Pub Date : 2024-09-24 DOI: 10.1016/j.matchar.2024.114393

TiZrHf-based refractory high entropy alloys (RHEAs) are becoming the focus in advanced metal materials owing to the excellent mechanical properties under the condition of medium and high temperatures. Nevertheless, the strength of TiZrHf-based RHEAs at medium temperatures has hindered the further application. This work proposed a novel approach to improve the mechanical properties of TiZrHf-based RHEAs. An innovative series of Ti₄₀Zr₂₀Hf_40-xCr_x (x = 19, 24 and 29, denoted by HfCr19, HfCr24 and HfCr29, respectively) eutectic refractory high entropy alloys (ERHEAs) were designed and prepared. The designed Ti₄₀Zr₂₀Hf_40-xCr_x alloys can form lamellar eutectic structure including BCC/HCP phase and Laves precipitating phase in solidification with the decrease of Hf/Cr ratio. The microstructure of HfCr19 and HfCr24 alloys was composed of BCC, HCP and Laves phase, while the HfCr29 alloy consisted of BCC and Laves phase. The formation of HCP phase in the Ti₄₀Zr₂₀Hf_40-xCr_x alloy were attributed to the lattice of Ti_0.5Zr_0.5 phase reconstruction during the rapid cooling, which promoted the formation of isomers in the alloy. Hence, the part of BCC phase was transformed into HCP phase in the HfCr19 and HfCr24 alloys, and the lamellar eutectic structure consisted of BCC/HCP phase and Laves phase. In addition, compared with the near-eutectic HfCr19 and HfCr29 alloys, the HfCr24 alloy with a complete lamellar eutectic structure has higher compressive strength at room temperature, which can reach 1648.7 MPa. In addition, the compressive strength (1261.7 MPa) can still be achieved at 600 °C. This work successfully prepared a high-strength TiZrHf-based ERHEA, and the compression mechanical properties at room temperature and middle-high temperature were studied and analyzed.

TiZrHf 基难熔高熵合金（RHEAs）由于在中温和高温条件下具有优异的机械性能，正成为先进金属材料的焦点。然而，TiZrHf 基 RHEAs 在中温条件下的强度阻碍了其进一步应用。这项研究提出了一种改善 TiZrHf 基 RHEAs 机械性能的新方法。设计并制备了一系列创新的 Ti40Zr20Hf40-xCrx（x = 19、24 和 29，分别用 HfCr19、HfCr24 和 HfCr29 表示）共晶难熔高熵合金（ERHEAs）。所设计的 Ti40Zr20Hf40-xCrx 合金在凝固过程中可形成片状共晶结构，包括 BCC/HCP 相和拉韦斯析出相，且随着 Hf/Cr 比的降低而降低。HfCr19 和 HfCr24 合金的微观结构由 BCC、HCP 和 Laves 相组成，而 HfCr29 合金则由 BCC 和 Laves 相组成。Ti40Zr20Hf40-xCrx 合金中 HCP 相的形成是由于快速冷却过程中 Ti0.5Zr0.5 相的晶格重构，促进了合金中异构体的形成。因此，在 HfCr19 和 HfCr24 合金中，部分 BCC 相转变为 HCP 相，片状共晶结构由 BCC/HCP 相和拉韦斯相组成。此外，与近共晶的 HfCr19 和 HfCr29 合金相比，具有完整片状共晶结构的 HfCr24 合金在室温下具有更高的抗压强度，可达 1648.7 兆帕。此外，在 600 ℃ 时仍能达到抗压强度（1261.7 兆帕）。本研究成功制备了一种高强度的 TiZrHf 基 ERHEA，并对其室温和中高温下的压缩力学性能进行了研究和分析。

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