STM和AFM的研制

叙述ＳＴＭ（扫描隧道显微镜）和ＡＦＭ（原子力显微镜）的主要关键技术和研制情况。在研制的ＳＴＭ和ＡＦＭ样机上，对１２００１／ｍｍ光栅进行测量，得出本样机的测量重复性可达１０％以内。对研制的样机进行分析和对比后提出：ＳＴＭ和ＡＦＭ，尤其是ＡＦＭ，技术上已趋于成熟；使用上简单、方便，已达到实用化程度，可以作为高级表面粗糙度测量的常用计量仪器。     

基于CAM的STM和AFM的一种过载保护装置研究

根据SIM和AFM的扫描原理,通过CAM设计了一种过载保护装置,使STM和AFM在测试过程中,对超过测试高度的样品停止退针,以免损坏仪器,弥补了仪器设计的不足.     

Atom probe tomography of reactor pressure vessel steels: an analysis of data integrity

In this work, the importance of optimising experimental conditions for the analysis of reactor pressure vessel (RPV) steels using atom probe tomography is explored. The quality of the resultant atom probe data is assessed in terms of detection efficiency, noise levels and mass resolution. It is demonstrated that artefacts can exist even when experimental conditions have been optimised. In particular, it is shown that surface diffusion of some minority species, including P and Si, to major poles prior to field evaporation can be an issue. The effects were most noticeable during laser pulsing.The impact of surface migration on the characterisation of dislocations and grain boundaries is assessed. The importance of selecting appropriate regions of the reconstructed data for subsequent re-analysis is emphasised.     

Atomic scale investigation on the distribution of boron in medium carbon steels by atom probe tomography and EELS

The medium carbon (0.5 wt% C) steels containing various boron contents were studied to observe the distribution of boron using atom probe tomography and electron energy loss spectroscopy. APT revealed the segregation of boron atoms at retained austenite for 100 ppm boron added steels and the trapped carbon atoms at micro-twins for 50 ppm boron treated steels. Moreover, it was also found that boron was randomly distributed for 20 ppm boron added steels regardless of the interactions between carbon and boron.     

Atom probe tomography characterization of heavily cold drawn pearlitic steel wire

Atom Probe Tomography (APT) was used to analyze the carbon distribution in a heavily cold drawn pearlitic steel wire with a true strain of 6.02. The carbon concentrations in cementite and ferrite were separately measured by a sub-volume method and compared with the literature data. It is found that the carbon concentration in ferrite saturates with strain. The carbon concentration in cementite decreases with the lamellar thickness, while the carbon atoms segregate at dislocations or cell/grain boundaries in ferrite. The mechanism of cementite decomposition is discussed in terms of the evolution of dislocation structure during severe plastic deformation.     

Atom probe tomography and transmission electron microscopy characterisation of precipitation in an Al-Cu-Li-Mg-Ag alloy

State-of-the art atom probe tomography (APT) combined with transmission electron microscopy (TEM) were used to investigate the microstructure at different stages of the ageing process of an alloy of composition (at%) Al-1.68%Cu-4.62%Li-0.33%Mg-0.1%Ag. These alloys were shown to exhibit a complex microstructure of T₁ plates and several metastable phases, including θ′ and S. We will highlight the early stages of clustering, precipitate interactions and possible solute segregation at the matrix/precipitate interfaces and detail the chemical composition of the different phases.     

Precipitation evolution in a Ti-free and Ti-containing stainless maraging steel

Stainless maraging steels have a Cr content higher than 12 wt% and show a excellent combination of high strength and ductility, which make them attractive for use in machinery fields and aircraft applications. The massive increase of strength during ageing treatment of maraging steels is related to a precipitation sequence of various nm-scaled intermetallic phases. The peak hardness especially in Ti-containing maraging steels can be reached after short-time ageing at temperatures around 500 °C.     

Atom probe tomography and transmission electron microscopy of a Mg-doped AlGaN/GaN superlattice

The electronic characteristics of semiconductor-based devices are greatly affected by the local dopant atom distribution. In Mg-doped GaN, the clustering of dopants at structural defects has been widely reported, and can significantly affect p-type conductivity. We have studied a Mg-doped AlGaN/GaN superlattice using transmission electron microscopy (TEM) and atom probe tomography (APT). Pyramidal inversion domains were observed in the TEM and the compositional variations of the dopant atoms associated with those defects have been studied using APT. Rarely has APT been used to assess the compositional variations present due to structural defects in semiconductors. Here, TEM and APT are used in a complementary fashion, and the strengths and weaknesses of the two techniques are compared.     

Friction and adhesion of stainless steel strip against tool steels in unlubricated sliding with high contact load

The strong tendency of stainless steel to adhere to other metals and to work harden makes it particularly difficult to form. A new slider-on-strip tribometer was used to study the tribological behaviour of traditional and new tool materials. The tribometer allows friction, workpiece adhesion on the tool surface and wear to be studied under conditions with low sliding speeds and high contact pressures. Several tool steels were tested using cold rolled stainless steel strip as a workpiece material. The results showed that the composition of the tool steel does not have a marked effect on the friction between the tool and the workpiece. However, the surface roughness and topography of the tool have a marked effect. Polishing of the tool surface to reduce the surface roughness reduces the friction between the tool and the workpiece.     

Study on the oxidation of stainless steels 304 and 304L in humid air and the friction during hot rolling

In rolling process, the contact friction is of crucial importance for accurate modeling, optimum design and control of industrial rolling processes. It is important to characterize the features of the oxide scale of stainless steel in hot strip rolling because the scale on the strip surface affects friction coefficient and thermal conductivity coefficient. To some extent, the rolling force and friction condition depend on the thickness and the microstructure of the oxide scale. Oxidation tests of stainless steels 304 and 304L were carried out in a high temperature electric resistance furnace. The humid air in which the water vapour content can be controlled was generated and remained to flow into the chamber of the furnace in 2.5 × 10⁻⁴ m³/s to study the effect of humidity on the oxidation of stainless steels. The microstructure and thickness of oxide scale layer of stainless steels were obtained and two or three oxide layers can be found. The humid air has a significant effect on the growth of oxide scale. Hot rolling tests were carried out on Hille 100 rolling mill. The friction condition at the roll–strip interface during hot rolling of stainless steel was determined and the transfer of surface roughness was discussed.     

Comparison of radiation-induced segregation in ultrafine-grained and conventional 316 austenitic stainless steels

Due to a high number density of grain boundaries acting as point defect sinks, ultrafine-grained materials are expected to be more resistant to irradiation damage. In this context, ultrafine-grained 316 austenitic stainless steel samples have been fabricated by high pressure torsion. Their behavior under ion irradiation has been studied using atom probe tomography. Results are compared with those obtained in an ion irradiated conventional coarse-grained steel. The comparison shows that the effects of irradiation are limited and that intragranular and intergranular features are smaller in the ultrafine-grained alloy. Using cluster dynamic modeling, results are interpreted by a higher annihilation of point defects at grain boundaries in the ultrafine-grained steel.     

Effect of sliding wear on tribocorrosion behaviour of stainless steels in a Ringer's solution

The dependence of the tribocorrosion of stainless steels AISI 304L and SS 3M^® orthodontic archwires sliding against corundum in a Ringer's solution on applied normal force, and sliding velocity, has been investigated using in situ electrochemical noise measurements. Applied normal force and sliding velocity were found to greatly affect current and potential during fretting-corrosion. An increase in normal force and sliding velocity induce an increase in current and a decrease in potential accelerating the depassivation rate of the tested stainless steels. The fluctuations in potential and current during fretting-corrosion are more pronounced at increasing sliding frequency than at increasing applied normal force. Sliding wear affects the repassivation behaviour of the tested materials by increasing the anodic current in the wear track area.     

Optimisation of specimen temperature and pulse fraction in atom probe microscopy experiments on a microalloyed steel

This paper details the effects of systematic changes to the experimental parameters for atom probe microscopy of microalloyed steels. We have used assessments of the signal-to-noise ratio (SNR), compositional measurements and field desorption images to establish the optimal instrumental parameters. These corresponded to probing at the lowest possible temperature (down to 20 K) with the highest possible pulse fraction (up to 30%). A steel containing a fine dispersion of solute atom clusters was used as an archetype to demonstrate the importance of running the atom probe at optimum conditions.     

Application of Taguchi coupled Fuzzy Multi Attribute Decision Making (FMADM) for optimizing surface quality in turning austenitic and duplex stainless steels

In the present study, Taguchi approach is coupled with fuzzy-multiple attribute decision making methods for achieving better surface quality in constant cutting speed face turning of EN 1.4404 austenitic, EN 1.4462 standard duplex and EN 1.4410 super duplex stainless steels. Two typical multiple attribute decision making techniques were simultaneously adopted to determine multi-surface quality characteristics indices. The differences in rankings among derived indices are solved through converting each crisp values into trapezoidal fuzzy number and unifying them using fuzzy simple additive weight method. The fuzzy numbers are then deffuzified into crisp values employing techniques like; the spread, mode and area between centroid of centroids. Through this procedure, the decision maker is provided with necessary decision tools to optimize the cutting conditions with less sensitivity to the change of weights and no difference in ranking among the deffuzification techniques. Additionally, results of analyses of means and the validation experiments confirm that the optimum cutting conditions derived by this method produce far better surface finish than the best finish obtained during the course of experimentation. Analyses of variance results have shown the predominant effect of feed rate on surface quality. Finally, the collected chip at constant cutting speed and varying feed rates and depth of cuts has shown that friendlier-to-machine chips are obtained when machining austenitic stainless steels than duplex stainless steel grades.     

基于STM32和LabVIEW的埋地钢质管道杂散电流检测系统

杂散电流干扰是影响埋地钢质管道安全运行的重要因素。针对现有杂散电流检测设备功能单一,精度不高,配置软件易用性差等问题,设计了一种基于STM32和LabVIEW的埋地钢质管道杂散电流检测系统,能够同时测量多种杂散电流干扰评价指标。该系统由采集系统和上位机两部分组成,采用模块化方式设计采集系统硬件电路,采用LabVIEW软件和MATLAB软件联合编程搭建上位机。实验结果表明,系统测量误差小于0.1%,满足标准要求。该系统具有现场应用推广的可行性。     

Shaping the lens of the atom probe: fabrication of site specific, oriented specimens and application to grain boundary analysis

The random sampling provided by classical atom probe sample preparation methods is one of the major factors limiting the types of problems that can be addressed using this powerful technique. A focused ion beam enables not only site-specific preparation, but can also be used to give the specimen, which acts as the lens in an atom probe experiment, a specific shape. In this paper we present a technique that uses low accelerating voltages (10 and 5 kV) in the focused ion beam (FIB) to reproducibly produce specimens with selected grain boundaries <100 nm from the tip at any desired orientation. These tips have a high rate of successfully running in the atom probe and no Ga contamination within the region of interest.This technique is applied to the analysis of grain boundaries in a high purity iron wire and a strip-cast steel. Lattice resolution is achieved around the boundary in certain areas. Reconstruction of these datasets reveals the distribution of light and heavy elements around the boundary. Issues surrounding the uneven distribution of certain solute elements as a result of field-induced diffusion are discussed.     

Ultrastructural effect of self-ligating bracket materials on stainless steel and superelastic NiTi wire surfaces

Frictional interactions between wires and brackets reduce the efficacy in orthodontic treatments. Self‐ligating brackets (SLBs) are now more often used due to lower frictional forces when compared with conventional‐ligating brackets. In this study, scanning electron microscopy and atomic force microscopy were used to examine the microstructural effects of stainless steel and ceramic SLBs on the surface roughness of stainless steel and superelastic NiTi wires both after in vivo clinical orthodontic treatment as well as in in vitro three‐point bending experiments. A combination of two wires—0.019 in. × 0.025 in. stainless steel wires and 0.016 in. superelastic NiTi wires—and two SLBs—both passive‐type stainless steel SLBs and active‐type ceramic SLBs—was applied for 4 months (bicuspid‐extraction) in an in vivo setting and for 1 month in an in vitro setting (200 g loads). After the SLB treatments, all wires exhibited severe scratches secondary to frictional interactions with the brackets. When used with the stainless steel SLBs (Damon 3MX®), the surfaces of 0.019 in. × 0.025 in. stainless steel (P < 0.0001) and 0.016 in. superelastic NiTi wires (P < 0.05) were significantly smoother than when used with the ceramic SLBs (Clippy‐C®). Such results suggest that orthodontic treatments with stainless steel SLBs are more effective than with ceramic SLBs. Microsc. Res. Tech. 75:1076–1083, 2012. © 2012 Wiley Periodicals, Inc.     

Evidence of commensurate contact and rolling motion: AFM manipulation studies of carbon nanotubes on HOPG

We report on experiments in which multiwall carbon nanotubes (CNTs) are manipulated with AFM on a graphite (HOPG) substrate. We find certain discrete orientations in which the lateral force of manipulation dramatically increases as we rotate the CNT in the plane of the HOPG surface with the AFM tip. The three-fold symmetry of these discrete orientations indicates commensurate contact of the hexagonal graphene surfaces of the HOPG and CNT. As the CNT moves into commensurate contact, we observe the motion change from sliding/rotating in-plane to stick–roll motion.     

基于STM32的便携式温、湿、压监测系统设计

为了满足应急气象监测提供及时准确的气象数据的需要,本文设计了一种基于STM32微控制器的便携式温湿压监测系统。该系统采用体积小、重量轻、功耗低的传感器采集温湿压数据,可连续对环境温度、湿度及气压进行观测,并在液晶屏上实时显示数据信息。同时使用C#语言编写上位机软件,实现温湿压数据的接收、显示及存储。该系统具有便携性、精度高、实时性好等特点,可作为应急气象监测系统的一部分进行温湿压监测。