Quasi-In-Situ EBSD Observation of the Orientation Evolution in Polycrystalline Tantalum During Rolling Deformation

The evolution of crystallographic orientation of polycrystalline tantalum(Ta) during rolling was characterized by electron backscatter diffraction technique in a quasi-in-situ way, and the microstructure and microtexture before and after the deformation were characterized and analyzed, respectively.In the specimen, 164 individual grains were exacted singly from the testing region and their corresponding orientations were reconstructed and analyzed, respectively.Results show that the heterogeneous deformation in a grain can be reflected by the accidented surface microstructure.Moreover, the orientations close to {111} orientations came closer to the {111} corner, while the orientation evolution is more complicated for the orientations close {100} corner, indicating that the evolution of these orientations close to {100} corner seemed to be irregular.     

EBSD技术研究Ni-48Al金属间化合物超塑变形组织演变

采用电子背散射衍射(EBSD)技术研究在1075℃、初始应变速率1.5×10-3s-1条件下大晶粒Ni-48Al合金超塑变形过程中的组织演变。结果表明,变形前,大晶粒Ni-48Al合金以大角度晶界为主,小角度晶界比例极低。在超塑变形过程中,持续有取向差≤5°的小角度晶界产生。随变形量的增大,新形成的小角度晶界取向差增加,转变为取向差6°~15°小角度晶界,进而转变为取向差>15°的大角度晶界。小角度晶界的产生速率与小角度晶界转变为较大角度晶界的速率趋向一动态平衡。小角度晶界向较大角度晶界不断转变的结果使大角度晶界数量不断增加,最终导致晶粒显著细化。     

原位生成Al2O3增强Al-4Mg基复合材料中的Al2O3/Al位向关系

综合搅拌铸造法和原位反应制备了Al2O3颗粒增强Al-4Mg基复合材料，并对制备的Al-4Mg基复合材料进行了透射电镜(TEM)观察分析，发现Al2O3／Al之间不存在固定的位向关系，但存在如下优先的位向关系：(1210)Al2O3∥(111)Al，[1012]Al2O3∥[112]Al，[2021]Al2O3∥[101]Al．     

In Situ Electron Backscatter Diff raction Analysis for Microstructure Evolution and Deformation Models of Mg–Ce Alloy During Uniaxial Loading

Previous studies showed that signifi cant increases in elongation in Mg–Ce alloys due to the Ce addition and the solute drag eff ect by Ce addition were ascribed to the non-basal dislocation slip activating and the texture altering. The microstructure evolution and deformation models of extruded Mg-0.5 wt%Ce alloy rods under uniaxial tension have been studied using in situ electron backscatter diff raction. The basal and non-basal slips were characterized by using slip line trace analysis. The results provide evidence for that pyramidal slip activated during deformation, besides basal slip and extension twinning, which contributes to the texture weakening and ductility increasing in Mg-0.5 wt%Ce alloy.     

高铌TiAl合金蠕变变形的原位观察

研究了近片层Ti-45Al-8Nb-0.2W-0.2B-0.1Y合金在750和800℃时短时蠕变行为,并进行了扫描电镜原位观察。结果表明:在750℃蠕变时,合金具有稳定的蠕变特征,随应力提高,稳态蠕变阶段变短,其蠕变应力指数为7.5;在800℃蠕变时,低应力下具有明显的稳态蠕变阶段,其蠕变应力指数为4.0,而高应力下几乎没有稳态蠕变,直接进入加速蠕变。SEM原位观察表明,其蠕变损伤过程是微裂纹的形成、长大及相互连接;随温度升高,裂纹扩展和连接速度变快。     

NiTi-NbTi原位复合材料的Lüders带型变形和载荷转移行为

采用电弧熔炼、锻造和拔丝方法原位合成了一种高Nb含量的NiTi-NbTi记忆合金复合材料.TEM显微分析显示,在材料内部纳米尺度的NbTi和NiTi纤维沿丝材轴向交替分布,NbTi纤维体积分数高达约70％.通过同步辐射高能X射线原位拉伸实验研究了复合材料的变形机制.结果显示,虽然NiTi体积分数仅约30％,但复合材料的...     

In Situ Phase Evolution of Ni/Ti Reactive Multilayers

Joining shape-memory alloys (SMA) to other materials is strongly required in order to enlarge their fields of application. Fusion welding induces strong compositional and microstructural changes that significantly affect the shape-memory effect and the superelastic behavior of these alloys. The exothermic and in some cases self-propagating character of some nano-multilayer reactions is explored in this study as an alternative for joining SMA. To follow these very fast reactions, high brilliance sources, such as synchrotron radiation, are required. In situ high-resolution x-ray diffraction data, giving the phase evolution sequence with temperature of the Ni/Ti multilayer thin films under study, are presented. A correlation between the multilayer design and the tendency for the sequence of phase formation is established.     

大变形Cu-10Ag原位纳米纤维复合材料

以不同的凝固速率制备了Cu-10Ag亚共晶合金。铸态结构由初生Ag沉淀,(Cu+Ag)共晶和Cu相组成。采用大变形制备了Cu-10Ag合金原位纤维复合材料。其中由初生Ag沉淀相所形成的Ag纤维具有较大直径(d)并可用幂指数关系d=C·exp(-0.228η)拟合,式中η是真实应变,C是与合金原始晶体尺寸有关的系数,而由(Cu+Ag)共晶中的Ag层所形成的Ag纤维具有更细直径(几纳米)。低温中间热处理可进一步细化Ag纤维尺寸和改进性能。经热机械处理的Cu-10Ag合金原位纳米纤维复合材料具有高强度(σb＞1.5 GPa)和高电导率(＞60％IACS)。大变形Cu-10Ag合金原位纳米纤维复合材料显示了两阶段强化效应。讨论了影响Ag纤维尺寸的因素和复合材料的强化与形变机制。     

右美托咪定对胃癌根治术中瑞芬太尼复合丙泊酚全麻药量及麻醉效果的影响——评《癌痛治疗学》

采用原位中子衍射分析技术测试了板条马氏体钢的拉伸塑性行为,采用Z-Rietveld和卷积多重全曲线拟合方法对衍射数据进行拟合分析.板条马氏体内的位错为刃、螺型位错的混合位错,并呈现随机分布特征.马氏体的加工硬化需要同时考虑位错密度和位错类型2个因素的作用.随着拉伸应变量的增加,螺型位错数量减少,刃型位错数量增加,总位错密度增加.硬取向板条束内位错密度增加,呈现加工硬化特征;软取向板条束内位错密度降低,出现加工软化特征.外加应力在硬取向和软取向板条束内产生应力再分配,变形后在板条束内形成长程内应力.     

In Situ X-ray Diffraction Study of the Tensile Deformation of U-5.8Nb Alloy

为了探明a2相U-5.8wt%Nb合金的晶格响应和变形特性,对力学拉伸加载下的合金变形行为进行了原位的X射线衍射（XRD）研究,获得了合金从弹性变形直至断裂的过程中晶格对外加应力的响应特征。实验中,每增加一定变形量就对试样进行原位的XRD分析,用单峰拟合法和Rietveld全谱精修方法处理数据,分析了合金变形过程中的晶格演化行为。结果显示,拉伸过程中,试样的晶胞参数、衍射峰强度和晶面间距都随外加应变有规律地变化。晶格响应分析结果表明,合金晶胞各方向弹性极限的显著差异是第一屈服平台形成的内在原因,该屈服平台的变形过程包括了孪生变形和弹性变形2种机制。利用研究结果能够很好地解释合金的形状记忆效应。     

Dynamic Deformation Behaviors of an In Situ Ti-Based Metallic Glass Matrix Composite

Quasi-static and dynamic deformation behaviors, fracture characteristics, and microstructural evolution of an in situ dendrite-reinforced metallic glass matrix composite: Ti₅₀Zr₂₀V₁₀Cu₅Be₁₅ within a wide range of strain rates are investigated. Compared with the quasi-static compression, the yielding stress increases, but the macroscopic plasticity significantly decreases upon dynamic compression. The effects of the strain rate on strain hardening upon quasi-static loading and flow stress upon dynamic loading are evaluated, respectively. The Zerilli-Armstrong (Z-A) model based on dendrite-dominated mechanism is employed to further uncover the dependence of the yielding stress on the strain rate.     

In Situ Observation of the Dislocation Structure Evolution During a Strain Path Change in Copper

The evolution of deformation structures in individual grains embedded in polycrystalline copper specimens during strain path changes is observed in situ by high-resolution reciprocal space mapping with high-energy synchrotron radiation. A large number of individual subgrains is resolved; their behavior during the strain path change is revealed and complemented by the analysis of radial x-ray peak profiles for the entire grain. This allows distinction between two different regimes during the mechanically transient behavior following the strain path change: Below 0.3% strain, the number and orientation of the resolved subgrains change only slightly, while their elastic stresses are significantly altered. This indicates the existence of a microplastic regime during which only the subgrains deform plastically and no yielding of the dislocation walls occurs. After reloading above 0.3% strain, the elastic stresses of individual subgrains are about the same as in unidirectionally deformed reference specimens. They increase only slightly during further straining—accompanied by occasional emergence of new subgrains, abundant orientation changes, and disappearance of existing subgrains.     

硬质合金中异常长大晶粒生长方向的EBSD研究

在硬质合金烧结过程中的晶粒异常长大是影响硬质合金产品质量的重要问题,本文采用EBSD分析硬质合金中异常长大晶粒的取向,结果表明:由于硬度大,样品进行金相抛光后可直接进行EBSD分析;粗晶晶粒生长完整,没有亚晶界;在烧结过程中,WC晶粒沿晶向{1120}﹤110﹥择优生长。     

Coupling of Electron Channeling with EBSD: Toward the Quantitative Characterization of Deformation Structures in the SEM

The coupling of electron channeling contrast imaging (ECCI) with electron backscatter diffraction (EBSD) provides an efficient and fast approach to perform ECCI of crystal defects, such as dislocations, cells, and stacking faults, under controlled diffraction conditions with enhanced contrast. From a technical point of view, the ECCI technique complements two of the main electron microscopy techniques, namely, EBSD and conventional diffraction-based transmission electron microscopy. In this review, we provide several application examples of the EBSD-based ECCI approach on microstructure characterization, namely, characterization of single dislocations, measurement of dislocation densities, and characterization of dislocation substructures in deformed bulk materials. We make use of a two-beam Bloch wave approach to interpret the channeling contrast associated with crystal defects. The approach captures the main features observed in the experimental contrast associated with stacking faults and dislocations.     

In Situ Transmission Electron Microscopy Observations of the Growth Process of Fe_3O_4–Ag Nanoparticles

The properties of nanocrystals are highly dependent on their morphology, composition and structure. To obtain full control over their properties, the behavior of nanocrystals under external stimuli, such as heat treatment, needs to be understood. Herein, to in situ observe their microstructure and morphology changes, Fe_3O_4–Ag heterodimers were selected as a model system. Their structural changes after heat treatment were investigated by in situ transmission electron microscopy. A combination of real-time imaging with elemental analysis enabled observation of the transformation of Fe_3O_4–Ag heterodimers having a loose interface configuration to those with a Janus structure at the atomic scale after heating from room temperature to 600 °C. After incubation at 600 °C for 32 min, two kinds of Janus structures could be seen, including a clear linear interface in the Fe_3O_4–Ag heterodimers and a semi-crescent-shaped interface between the Ag and Fe_3O_4 nanoparticles(NPs). These dynamic observations provide unique insights into NP growth mechanisms, which are essential for understanding and controlling the structure and morphology of nanoparticles.     

形变铜基原位复合材料研究与展望

形变铜基原位复合材料具有超高的强度和良好的导电性,是高性能铜基材料发展的重要方向。综述了形变铜基原位复合材料的国内外研究现状,介绍了它的制备方法、组织演变、强化和导电机理,并对该类材料的研究方向进行了展望。     

In Situ Investigation of Dendrite Deformation During Upward Solidification of Al-7wt.%Si

The in situ investigation of dendrite deformation during solidification processing is an ongoing challenge because of the technical difficulties in carrying out experimental observations and direct measurements in metallic systems that are opaque to visible light and have a high melting temperature. Over the last 20 years, x-ray imaging has been established as a method of choice to overcome this experimental barrier by taking advantage of the increased capabilities of third-generation synchrotron x-ray sources, providing information on growth process and semisolid deformation that is not available otherwise. In this article, we present results showing that the unique combination of synchrotron x-ray radiography and synchrotron white beam x-ray topography can help to reveal the deformations that dendritic microstructures undergo during the upward directional solidification of Al-7wt.%Si alloys. Particular focus will be placed on the bending phenomena of dendrites because of gravity, which may precede fragmentation in the case of well-developed secondary arms.