Cr、Mo元素对12Cr1MoV钢基体强化作用的电子理论研究

应用余氏理论(EET)计算了从20℃到700℃不同温度下，Cr、Mo元素固溶于12Cr1MoV钢基体的价电子结构，发现随温度升高，各结构单元的结合强度下降。从价电子结构层次分析了Cr、Mo对基体的强化作用。Cr、Mo溶入基体后不仅增强了A键，也增强了B键，使同温度的nA、nB值都有所增加，提高了α固溶体的原子键引力，从而强化了α固溶体，而且Mo的作用大于Cr。     

降低渗硼层本质脆性对其摩擦磨损特性的影响

以固体与分子经验电子理论（EET理论）为指导,采用MM—200型磨损试验机对比研究了称为渗硼层的Fe2B相和含铬Fe2B相的价电子结构以及它们的摩擦磨损特性。结果表明,与Fe2B相相比,含铬Fe2B相的价电子结构发生了变化,导致弱键B—B键的成键能力得以提高、渗硼层的本质脆性得以改善;渗硼层本质脆性的下降提高了它的承载能力和耐磨性,而且还具有一定的减摩作用。同时对磨损机理进行了分析讨论。     

Nb对Ti3Al价电子结构及其脆性的影响

应用固体与分子经验电子理论计算了Ti3Al及加入Nb后各相的价电子结构,并从均匀变形因子α、解理能Gc及位错行为等方面分析了Nb对Ti3Al脆性的影响。结果表明,Nb使α2相部分无序化,产生新的韧性相,提高了Ti3Al合金的α和Gc值;同时Nb也减弱了Ti-Ti共价键,增加了基面滑移,从而综合导致Ti3Al脆性有本质改善。     

镍基高温合金电子空位数计算的新方法与组织稳定性预测

介绍了一种计算高温合金电子空位数的新方法，并用来预测了5种典型镍基高温合金的组织稳定性及拓扑密排相（TCP相）的析出趋势。结果表明：用电子空位数计算新方法预测合金基体中TCP相的析出趋势比较准确，但不适用于预测合金渗层扩散区TCP相的析出趋势。     

银合金化镁钙合金中AgMg、Mg_2Ca和AgCa相的第一性原理计算

采用基于密度泛函理论(DFT)的Materials Studio中的CASTEP模块,对银合金化镁钙合金中AgMg、Mg2Ca、AgCa相的热力学性质、电子结构和弹性性质进行了第一性原理计算,将计算得到的合金形成热、结合能、体模量、剪切模量、弹性模量、泊松比、熔点和硬度与文献值进行了对比。结果表明:AgMg相的结合能力最强,结构最稳定,抵抗变形能力和抗剪切能力最强,熔点和硬度最高;AgCa相的塑性和延展性要高于其它两相的;计算结果与文献值相差不大,证明了计算结果的正确性。     

热喷涂TBCs涂层对高温合金组织结构影响的研究

针对热喷涂前后高温合金基体材料金相组织变化，以及喷涂热障涂层（英文缩写：TBCs）后合金基体材料在瞬时高温下的组织结构变化开展研究。结果表明热喷涂TBCs涂层过程中，高温合金基体材料组织没有明显结构变化；在1300K温度下，10min后的高温合金组织会形成枝晶状并析出二次γ相，而同等条件下，采用热喷涂TBCs涂层保护后的高温合金基体材料的组织没有发生明显的变化。     

相场法研究化学组成对Ni-Al-Ti合金γ′相早期沉淀过程的影响

通过微观相场动力学模型研究了化学组成对Ni-Al-Ti合金γ′相早期沉淀过程的影响. 研究结果表明, 在γ′相形成之前, 基体内部先析出L10结构的过渡相.随着Al成分的不断升高, 沉淀相组成逐渐由γ′相与基体相两相共存变为单一的γ′相, 同时大量的Al会促进γ′相的形成, 从而引起体积其体积分数增大, 但L10相向L12相的转化时间有所延长. 通过分析Ti原子占位情况发现, 随Ti含量的减少, Ti的固溶强化作用有所减弱.     

时效温度对LF9合金组织与性能的影响

研究了在不同温度时效后LF9合金组织与性能的变化。结果表明：在相同保温时间下,随着时效温度的升高,合金的室温和高温拉伸强度均升高,塑性、冲击功均下降;时效后合金的主要析出相为γ＇、M23C6、MC相;主要强化相γ’的析出量随时效温度的升高而增加,当温度低于720℃时,γ’相析出量增加显著,温度高于720℃时,析出量的增...     

降低渗硼层本质脆性对其磨粒磨损特性的影响

利用MM-200型磨损试验机,研究了通过固体硼铬稀土共渗降低渗硼层本质脆性对其磨粒磨损特性的影响。并进行了应用试验,同时利用固体与分子经验电子理论对含铬Fe2B相的价电子结构进行了分析,结果表明,脆性的下降可使渗硼层的耐磨粒磨损性能提高0.27-0.80倍,而且实际应用效果显著,铬原子的溶入改变了Fe2B相的价电子结构,从而使渗硼层的本质脆性降低。     

相场法研究化学组成对Ni-Al-Ti合金γ′相早期沉淀过程的影响（英文）

通过微观相场动力学模型研究了化学组成对Ni-Al-Ti合金γ′相早期沉淀过程的影响。研究结果表明,在γ′相形成之前,基体内部先析出L1_0结构的过渡相。随着Al成分的不断升高,沉淀相组成逐渐由γ′相与基体相两相共存变为单一的γ′相,同时大量的Al会促进γ′相的形成,从而引起体积其体积分数增大,但L1_0相向L1_2相的转化时间有所延长。通过分析Ti原子占位情况发现,随Ti含量的减少,Ti的固溶强化作用有所减弱。     

Comparison of different models for the generation of electron backscattering patterns in the scanning electron microscope

An electron backscattering pattern (EBSP) is formed on a fluorescent (or other) screen from the faster scattered electrons when a single-crystal region of a solid sample is illuminated by a finely focused electron beam (EB). The EBSP is very similar in appearance to the electron channeling pattern (ECP) that is obtained in the scanning electron microscope (SEM) by rocking the beam about a point on the surface of a single crystal. It has been suggested that the mechanisms that give rise to EBSP and ECP are related by reciprocity. If this is indeed the case, then the models that are used to explain them should be the same except for the direction in which the electrons travel through the specimen. The two-event “diffraction model” for EBSP (diffuse scattering followed by diffraction) fails this condition, leading to the conclusion that the “channeling in and channeling out” model for EBSP is more likely to be correct. This has been described rigorously by Reimer (1979, 1985). It is named after the title used by Joy (1994). An attempt is made here to describe this model in a simple way.     

Enhanced angular current intensity from Schottky emitters

Even though the Schottky emitter is a high‐brightness source of choice for electron beam systems, its angular current intensity is substantially lower than that of thermionic cathodes, rendering the emitter impractical for applications that require high beam current. In this study, two strategies were attempted to enhance its angular intensity, and their experimental results are reported. The first scheme is to employ a higher extraction field for increasing the brightness. However, the tip shape transformation was found to induce undesirably elevated emission from the facet edges at high fields. The second scheme exploits the fact that the angular intensity is proportional to the square of the electron gun focal length [ Fujita, S. & Shimoyama, H. (2005) Theory of cathode trajectory characterization by canonical mapping transformation. J. Electron Microsc. 54 , 331–343], which can be increased by scaling‐up the emitter tip radius. A high angular current intensity (J_Ω∼ 1.5 mA sr⁻¹) was obtained from a scaled‐up emitter. Preliminary performance tests were conducted on an electron probe‐forming column by substituting the new emitter for the original tungsten filament gun. The beam current up to a few microamperes was achieved with submicron spatial resolution.     

A high signal-to-noise ratio toroidal electron spectrometer for the SEM

This paper presents a high signal-to-noise ratio electron energy spectrometer attachment for the scanning electron microscope (SEM), designed to measure changes in specimen surface potential from secondary electrons and extract specimen atomic number information from backscattered electrons. Experimental results are presented, which demonstrate that the spectrometer can in principle detect specimen voltage changes well into the sub-mV range, and distinguish close atomic numbers by a signal-to-noise ratio of better than 20. The spectrometer has applications for quantitatively mapping specimen surface voltage and atomic number variations on the nano-scale.     

New developments in the characterization of dislocation loops from LACBED patterns

The characterization of the Burgers vector of dislocations from large‐angle convergent‐beam electron diffraction (LACBED) patterns is now a well‐established method. The method has already been applied to relatively large and isolated dislocation loops in semiconductors. Nevertheless, some severe experimental difficulties are encountered with small dislocation loops. By using a 2 µm selected‐area aperture and a carbon contamination point to mark the loop of interest, we were able to characterize both the plane and the Burgers vector of dislocation loops of a few tens of nanometres in size present in Al‐Cu‐Mg alloys.     

New system for secondary electron detection in variable-pressure scanning electron microscopy

A novel secondary electron detection system combining a two‐stage detector head and a differential pumping system is presented. The detector head consisted of a scintillation Everhart‐Thornley detector and a microsphere plate, separating it from the lower vacuum in the intermediate chamber (below 0.1 mbar). The system was arranged asymmetrically, which should contribute to a lower gas leakage through the plate and a longer life span of the plate. The system offered all the advantages of the scintillator detector in a wide range of gas pressures, from high vacuum to those of the order of 10 mbar, typical of high‐pressure scanning electron microscopy.     

Diffraction effects and inelastic electron transport in angle‐resolved microscopic imaging applications

We analyse the signal formation process for scanning electron microscopic imaging applications on crystalline specimens. In accordance with previous investigations, we find nontrivial effects of incident beam diffraction on the backscattered electron distribution in energy and momentum. Specifically, incident beam diffraction causes angular changes of the backscattered electron distribution which we identify as the dominant mechanism underlying pseudocolour orientation imaging using multiple, angle‐resolving detectors. Consequently, diffraction effects of the incident beam and their impact on the subsequent coherent and incoherent electron transport need to be taken into account for an in‐depth theoretical modelling of the energy‐ and momentum distribution of electrons backscattered from crystalline sample regions. Our findings have implications for the level of theoretical detail that can be necessary for the interpretation of complex imaging modalities such as electron channelling contrast imaging (ECCI) of defects in crystals. If the solid angle of detection is limited to specific regions of the backscattered electron momentum distribution, the image contrast that is observed in ECCI and similar applications can be strongly affected by incident beam diffraction and topographic effects from the sample surface. As an application, we demonstrate characteristic changes in the resulting images if different properties of the backscattered electron distribution are used for the analysis of a GaN thin film sample containing dislocations.     

反射电子抑制技术和新型电子枪(BS-60050EBS)

在使用电子束真空镀膜时所产生的反射电子有可能射入基板,造成MgF2等不稳定化合物薄膜吸收的增加,另外在使用萤石(CaF2)基板时则会造成基板变色等问题。BS-60050EBS电子枪优化了反射电子发生部分的磁场分布、能够有效地抑制反射电子射入基板、提高镀膜产品的质量。     

On the accuracy of lattice-distortion analysis directly from high-resolution transmission electron micrographs

Lattice‐distortion analysis from high‐resolution transmission electron micrographs offers a convenient and fast tool for direct measurement of strains in materials over a large area. In the present work, we have evaluated the accuracy of the strain measurement when the effects of the realistic experimental variables are explicitly taken into account by the use of image simulation techniques. These variables are focal setting and variation, local thickness and orientation of the sample, as well as misalignments of the sample and the incident beam. The evaluation reveals that consistency of image features and contrast within the micrographs is desired for the analysis to eliminate effects of the variations of local focus value and specimen thickness. After proper orientation of a crystalline specimen, the misorientation of the object will not notably influence the strain measurement even though a local bending may exist within the sample. However, the incident beam of the microscope needs to be aligned carefully as the beam misalignment may introduce a notable artefact around the interface region.     

Charging in scanning electron microscopy "from inside and outside"

This paper is an attempt to analyse most of the complicated mechanisms involved in charging and discharging of insulators investigated by scanning electron microscopy (SEM). Fundamental concepts on the secondary electron emission (SEE) yield from insulators combined with electrostatics arguments permit to reconsider, first, the widespread opinion following which charging is minimised when the incident beam energy E0 is chosen to be equal to the critical energy E(o)2, where the nominal total yield delta(o) + eta(o) = 1. For bare insulators submitted to a defocused irradiation, it is suggested here that the critical energy under permanent irradiation EC2 corresponds to a range of primary electrons, R, and nearly equals the maximum escape depth of the secondary electrons, r. This suggestion is supported by a comparison between published data of the SEE yield delta(o) of insulators (short pulse experiments) and experimental results obtained from a permanent irradiation for EC2. New SEE effects are also predicted at the early beginning of irradiation when finely focused probes are used. Practical considerations are also developed, with specific attention given to the role of a contamination layer where a negative charging may occur at any beam energy. The role of the various time constants involved in charging and discharging is also investigated, with special attention given to the dielectric time constant, which explains the dose rate-dependent effects on the effective landing energy in the steady state. Numerical applications permit to give orders of magnitude of various effects, and several other practical consequences are deduced and illustrated. Some new mechanisms for the contrast reversal during irradiation or with the change of the primary electron (PE) energy are also suggested.