Pore defects present a significant challenge to the industrial application of high-strength aluminum alloy components produced via additive manufacturing. In this study, single-track, single-layer, and bulk 2024 Al samples were fabricated using the laser directed energy deposition (L-DED), and the evolution of porosity during the layer-by-layer deposition was analyzed. The results show that, despite employing the same optimized process parameters, the porosity in bulk samples reached 2.9 %-3.7 %, which is 6-10 times higher than that observed in single-layer samples. Pores were primarily concentrated in the columnar dendrite region near the solidification front after depositing 3-4 layers, with approximately 73.2 % located along the fusion line, exhibiting a spatial distribution characteristic of "fewer at the bottom, more at the top". This trend is attributed to the remelting of underlying layers by subsequent deposition passes, which releases existing pores into the melt pool. These bubbles are then repeatedly recaptured by the advancing solidification front. With each cycle of remelting and recapture, porosity accumulates layer by layer. Based on the inherent thermal-physical properties of the material, a dimensionless parameter Se was introducted to evaluate the probability of melt pool bubbles being captured by the solidification interface during L-DED deposition of different materials. Comparative analysis with common structural materials, such as iron-, nickel-, and titanium-based alloys, revealed that aluminum alloys exhibit an Se value >1 within the selected temperature range, indicating their naturally high susceptibility to porosity. Pore formation in L-DED is governed by the interplay between bubble generation and escape within the melt pool. Bubble formation is closely associated with hydrogen precipitation, the presence of porous powder, entrainment of shielding gas, and the remelting of subsurface pores. These findings provides a reliable reference for reducing porosity and optimizing the L-DED process for aluminum alloys.

A common challenge in laser additive manufacturing of metal-matrix composites is balancing hardness with impact toughness while preventing cracking. In this study, 35CrMoV steel was selected as the matrix, and titanium carbide (TiC) ceramic particles were applied to prepare TiC/ iron-matrix composites. This approach aimed to achieve an optimal combination of refined microstructure, enhanced hardness, and improved impact toughness. The results showed that adding ceramic particles significantly refines the grain size of the matrix. As the ceramic volume fraction increased, the average grain size of the metal matrix gradually decreased, and the proportion of high-angle grain boundaries (HAGBs) rose. At a ceramic volume fraction of 60 %, the average grain size of the matrix decreased to 3 mu m, while the proportion of HAGBs increased to 81.93 %. Additionally, the impact toughness of the composites initially decreases and subsequently improves as ceramic content increases. In this case, the composite achieves high hardness and good impact performance. The hardness of the composites reached 2 to 3 times that of the matrix metal, while the impact energy attained 84 % of the matrix's level. The combined effects of grain refinement and the increased ratio of HAGBs enhance the composites' hardness and toughness. This work demonstrated significant potential for producing metal matrix composites that exhibit a unique combination of excellent wear resistance and impact toughness, making them suitable for practical applications.

The intragranular second phase is expected to overcome the bottleneck of plasticity in metal matrix composites caused by grain boundary distribution induced stress concentration. In this study, Al3Ti fine second-phasereinforced SiCp/Al joint was successfully prepared using the laser-friction stir technique. The mechanical properties and deformation mechanism of laminar s SiCp/Al joint was studied in detail. The second-phase particles were encapsulated inside the grains by the rapid solidification characteristic of laser metallurgy. Subsequently, the grains and the second phase underwent further refinement and violent deformation under the friction stir technology. Finally, Al3Ti and alpha-(Al,Mn) intragranular reinforcement phases were prepared. Tensile property tests results show that the maximum tensile strength of SiCp/Al joint attained is 325 +/- 12 MPa and the fracture elongation is 4.49 % +/- 0.44 %, which exceeds the reported properties of SiCp/Al joint. This study presents a new strategy for preparing fine second-phase-reinforced metal matrix composites.

采用电子探针显微分析法对光纤预制棒进行元素线分析定量化,光纤预制棒心部Yb和Al等元素的含量较低、基体效应的复杂影响以及测试条件的差异等因素导致线分析定量化结果误差较大.采用多点法的测试结果对光纤预制棒中Yb、Al元素的线分析定量化结果进行校正.结果表明:在两点法的基础上引入修正因子,可以简化测试过程,快速、准确地得到元素线分析定量化结果.

The WC/W2C eutectic reinforecement was applied to suppress the formation of interfacial reaction layer TiC in titanium matrix composites due to the lower interfacial reactivity between W2C and Ti. W solid solution interface was successfully produced at the WC/Ti interface, while the most readily formed compact reaction layer TiC was completely delimitated. Such W solid solution interface is more effective to transfer stress from the matrix to the particles than that of the TiC layer. Decohesion of the W interface was never occurred.

In this paper, a deflected laser welded joint of 304 stainless steel and T2 copper was studied concerning structural arrangement, grain structure and texture evolution. According to SEM and EBSD results, the as-welded fusion zone contained a major fraction of Fe-Cr-Ni rich alpha structure and minor fraction of Cu-rich epsilon structure. Furthermore, three types of epsilon were observed including blocky, curved and spherical forms. Both grain size and crystalline orientation varied largely from 304 side to T2 side. Additionally, epitaxial zone was progressively wider on 304 side than T2. In mixed zone, epsilon possessed comparably dispersed orientation and fine grains. Based on solidification sequence of delta -> Fe-Cr-Ni rich delta/gamma -> Cu rich gamma in the fusion zone, the dispersed primarily solidified of Fe-Cr-Ni rich spheres with random orientation led to the formation of fine grains in epsilon. As for alpha, the continuous growth of Fe-Cr-Ni rich bulks with uniform orientation promoted the identical growth and orientation of inside Cu rich spheres.

The microstructure and phase composition of 304 stainless steel fabricated by laser cladding are studied by scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The results show that the cladding layer is mainly composed of austenite (gamma) phase and FeCr (sigma) phase, and the atomic ratio of Fe to Cr in the sphase is close to 1:1. The gamma-phase is in the form of fine and dense dendrites, while the s phase is mainly in the form of long strips with a width of about 200 nm and locates in the dendritic interstices. During the rapid solidification of the cladding layer, the s phase precipitates from the inter-dendritic eutectic ferrite (delta). A large amount of gamma/delta interfaces formed by the inter-dendritic eutectic can effectively reduce the difficulty of nucleation of the sigma-phase, and the enrichment of the inter-dendritic Cr element can promote the formation and coarsening of the sigma-phase. Therefore, compared with the sigma-phase precipitated in the solid solution process of stainless steel, the sigma-phase precipitated in the laser cladding process has short formation time and large size.

Thermal fatigue is the main failure mode for chromium hot-work steels. In this study, pre-alloyed chromium hot-work steel powders with three different Cr, Mo, and V addition levels (low content (LH), medium content (MH), and high content (HH)) were used for selective laser melting (SLM). The microstructure and thermal fatigue properties of these SLM-processed materials were investigated. After thermal fatigue tests, LH possessed the lowest hardness (approximately 573 HV5) and longest crack length, MH possessed the highest hardness (approximately 688 HV5) and HH (with the hardness of approximately 675 HV5) possessed the shortest crack length. It can be concluded that the increase of V content in MH is the main reason for the refined grains which result in an enhanced hardness and thermal fatigue resistance compared to LH. The further increase of the Cr and Mo content in HH leads to the grain coarsening and hardness decreasing, which is supposed to degrade the thermal fatigue resistant properties according to the conventional theory. However, HH exhibited an enhanced thermal fatigue resistance compared to MH. That is because the higher stored energy in MH deteriorated its thermal fatigue resistance compared to HH.

在低倍率下对样品进行大面积EBSD测试时,常发现边缘区域标定率较低.为探究大面积EBSD分析中标定率低的影响因素,本文在100倍下选取同一采集区域,将其移至视野不同位置进行EBSD数据采集,结果表明,在测试参数不变的情况下,同一采集区域在不同位置时的标定率差别很大.甚至同一晶粒在不同位置采集时标定的取向也存在差异.分析发现,标定结果存在差异的主要原因是低倍率下,在视野中心电子束处于聚焦状态,而在边缘位置电子束处于散焦状态.电子束散焦时,束斑尺寸增大,激发的背散射电子在射出晶粒尺寸较小的样品表面时,在不同晶粒的不同晶面同时发生衍射,衍射花样会相互干扰,因而导致EBSD花样模糊、宽化、重叠,标定率变差.同时,较大的电子束束斑直径会降低EBSD空间分辨率,因而难以准确反映晶粒取向的细微变化.

为给有源光纤的工艺开发和性能研究提供有力支撑,该文利用场发射型电子探针EPMA-8050G对光纤纤芯的元素掺杂微区进行系统的定性定量分析,进一步研究石英基质的测试特点以及测试条件对样品烧蚀的影响.能谱仪(EDS)和波谱仪(WDS)的定性分析结果表明,分析含量较低的元素如稀土元素Yb和轻元素F时,WDS有明显的优势.状态分析结果表明,石英基质有源光纤的定量分析最佳条件为加速电压15?kV,束流20?nA.利用该文确定的定量分析方法测试两种有源光纤,成分总量均在100％±2％以内,在光纤类样品的分析中可以得到准确可靠的结果.

The traditional graphite anode with a specific capacity of 372 mA h g(-1) for lithium-ion batteries (LIBs) can't satisfy the increasing demands of energy density. Germanium (Ge) anode material has been considered as a promising candidate owning to its higher theoretical specific capacity (1600 mA h g(-1)). Unfortunately, lithiation/delithiation process of Ge produces a huge volume variation, resulting in poor electrochemical performances. Herein, we designed and prepared a unique Ge-based composite that immersing hetero-Cu3Ge/Cu into a nitrogen-doped carbon matrix (CG/G@NC). In this delicate architecture, both NC and electrochemically inert Cu3Ge act as conductive additives and volume buffers to improve conductivity and mitigate volume changes, respectively. Also, heterostructure possesses good charge transfer kinetics and offers an additional Li+ diffusion path. As result, the Li+ diffusion in CG/G@NC composite is similar to 930 times as fast as commercial Ge and similar to 320 times as fast as NC. As expected, the as-prepared CG/G@NC composite exhibits superior outstanding cycle stability (455 mA h g(-1) after 500 cycles at a constant current density 1000 mA g(-1)) and exceptional rate capability. Meaningfully, encapsulating Ge-based heterostructure materials with functional components into the carbon matrix is a promising method to facilitate the practical application of Ge-based anode materials. (C) 2020 Elsevier B.V. All rights reserved.

作为微区分析的有效手段,电子探针(EPMA)在材料成分的定性、定量、线分析以及元素面分布的分析方面等有着广泛的应用.特别是随着技术的不断进步,场发射型电子探针在同时获得高分辨率的图像和精确的成分分析方面有显著的优势,为材料分析提供了更多的可能性.本文以岛津EPMA-8050G型场发射型电子探针在材料分析中的典型应用为例,结合配备的能谱仪附件,对利用电子探针波谱仪和能谱仪进行材料的成分分析进行介绍和对比.另外,EPMA-8050G型电子探针配置的背散射电子探测器性能优异,能够初步观察材料的晶粒取向信息,可以用来分析和判断EBSD样品的前期制样效果,进一步扩展了电子探针在材料分析方面的应用.

为阐明加速电压对场发射扫描电子显微镜(FESEM)图像的影响,实验以4种典型材料为研究对象,比较了普通模式和电子束减速模式下不同加速电压的FESEM图像.结果表明:普通模式下,对低原子序数的样品进行FESEM表征时,宜选择较低的加速电压;对高原子序数样品或样品的内部相进行FESEM表征时,宜选择较高的加速电压.电子束减速模式在对不耐电子束的样品表征方面具有独特的优势.

The grain refinement mechanism and texture evolution of electromagnetically formed polycrystalline Cu sheets were investigated using the electron back-scattered diffraction (EBSD) technique. It is found that the average grain size decreases from 35.88 μm to 8.77 μm. The grain refinement was mainly attributed to dynamic recrystallization (DRX) at the grain boundary regions of bulged Cu samples where the inhomogeneous dislocation density and the large lattice misorientation were observed. The DRX mechanisms at the grain boundaries were discussed with respect to the strain-induced grain boundary migration nucleation. Moreover, the orientation distribution function (ODF) of the sample with the strain of 50% demonstrated a strong {110}<211> texture and a relatively weak {001}<100> texture. The texture evolution was discussed using the plastic work values of the grains with various orientations, which were calculated according to the Taylor model and the virtual work principle. The experimental results show that the expended plastic work of the grains with {110} orientation is 9.69 MPa, which is distinctly higher than those of the grains with the {001} and {111} orientations. This indicates that the formation of the {110} orientated texture would be preferred with increasing strain in good agreement with the experimental result.

The ammonium vanadium oxide cross-like nanobelt arrays with bamboo mat center were synthesized via hydrothermal method using NH4VO3 as precursors in presence of sodium carboxymethyl cellulose (CMC) at 160°C for 6h. Synthesized-products were characterized by XRD, FE-SEM, TEM, SA-ED, HR-TEM, and FT-IR. The effects of CMC concentration, pH value and temperature on the product morphology were investigated. pH value plays a crucial role in the formation of cross-like nanobelt arrays. Based on the results of time dependent experiments, the growth process of the cross-like NH4V4O10 nanobelt arrays is proposed. Furthermore, the mixed valance state vanadium oxide nanobelt arrays were obtained by calcination of the cross-like NH4V4O10 nanobelt arrays at 400°C for 40min and its capability of catalytic degradation of rhodamine B with oxygen in aqueous under UV/vis light irradiation was studied and compared with anionic dyes. The influence of temperature on the photocatalytic degradation was also investigated. The result showed that the degradation efficiency of rhodamine B catalyzed by the calcinated product was about 95% at pH 6.8 and 75°C for 3h and 30min, suggesting it is a candidate of efficient catalysts for the photocatalytic degradation of rhodamine B under visible light irradiation. © 2012 Elsevier B.V.

This paper focuses on the study of boundary misorientation,grain size,and texture of pure copper with different passages of equal channel angular pressing(ECAP)by means of EBSD.The results of this research indicate that with increase of the ECAP passages,the grains turn into ones with long axis from the original equiaxied crystals..Large amount of dislocations occur within the grains,which develop into sub-grains ultimately.Refined grains can be obtained by process of multi passages of ECAP.The grain size which is about 34μm originally decreases to about 6μm after 6 passages of ECAP.Meanwhile,due to the appearance of preferred orientation,fiber texture is discovered on 〈110〉.

Thin-layer electrochemical studies of the underpotential deposition (UPD) of Bi and Te on cold rolled silver substrate have been performed. The voltammetric analysis of underpotential shift demonstrates that the initial Te UPD on Bi-covered Ag and Bi UPD on Te-covered Ag fitted UPD dynamics mechanism. A thin film of bismuth telluride was formed by alternately depositing Te and Bi via an automated flow deposition system. X-ray diffraction indicated the deposits of Bi2Te3. Energy Dispersive X-ray Detector quantitative analysis gave a 2: 3 stoichiometric ratio of Bi to Te, which was consistent with X-ray Diffraction results. Electron probe microanalysis of the deposits showed a network structure that results from the surface defects of the cold rolled Ag substrate and the lattice mismatch between substrate and deposit.

The process of Sb 2 Te 3 thin film growth on the Pt substrate by electrochemical atomic layer epitaxy (ECALE) was studied. Cyclic voltammetric scanning was performed to analyze the electrochemical behavior of Te and Sb on the Pt substrate. Sb 2 Te 3 film was formed using an automated flow deposition system by alternately depositing Te and Sb atomic layers for 400 circles. The deposited Sb 2 Te 3 films were characterized by XRD, EDX, FTIR and FESEM observation. Sb 2 Te 3 compound structure was confirmed by XRD pattern and agreed well with the results of EDX quantitative analysis and coulometric analysis. FESEM micrographs showed that the deposit was composed of fine nano particles with size of about 20 nm. FESEM image of the cross section showed that the deposited films were very smooth and dense with thickness of about 190 nm. The optical band gap of the deposited Sb 2 Te 3 film was determined as 0.42 eV by FTIR spectroscopy, and it was blue shifted in comparison with that of the bulk Sb 2 Te 3 single crystal due to its nanocrystalline microstructure.

研究了利用电化学原子层外延法（electrochemical atomic layer epitaxy,ECALE）在Pt电极上生长Sb2Te3化合物半导体薄膜热电材料的过程.采用循环伏安扫描分别研究了Te和Sb在Pt衬底上以及在覆盖了一层元素之上的电沉积特性,在此基础上使用自动沉积系统交替电化学沉积了400个Te和Sb原子层.采用XRD,FESEM和FTIR等多种分析测试手段对沉积薄膜的结构、形貌、禁带宽等进行了表征.XRD结果表明,沉积物是Sb2Te3化合物,与EDX定量分析和电量计算结果吻合;FESEM对薄膜表面及断面形貌检测表明沉积颗粒排列紧密、大小均匀,平均粒径约为20nm,薄膜均匀平坦,膜厚约190nm;由于沉积薄膜的纳米结构,FTIR吸收谱出现蓝移,测得Sb2Te3薄膜禁带宽为0.42eV.

The Bi_2Te_3 thin film deposition on Au substrate using electrochemical atomic layer epitaxy(ECALE) is reported in this article.Cyclic voltammograms of Bi and Te on the Au substrate were performed to investigate electrochemical aspects of tellurium and bismuth.200 cycle deposits were formed by using an optimized deposition program.X-ray diffraction,EDX quantitative analysis and FESEM studies of the morphology of substrates and deposits indicated the stoichiometric ratio of Bi to Te is 2∶3;the deposits are Bi_2Te_3,not mixture of Bi and Te;the quality of the deposits are symmetrical,compact and glazed,with a(015) preferred orientation,which suggested an epitaxy growth mechanism of Bi_2Te_3 thin films has taken place.