Effect of sigma phase on near-threshold fatigue crack growth behavior and ultrasonic evaluation in AISI 316L stainless steel

In this work, we examined the influence of microstructural changes, such as an intermetallic sigma (??) phase, on the fatigue behavior of high-temperature aged AISI 316L stainless steel. Nondestructive ultrasonic test and fatigue crack growth tests were performed to determine the threshold stress intensity factor of these artificially aged specimens. Ultrasonic test results characterizing the microstructural changes were compared with those of the fatigue tests to propose an empirical formula capable of predicting the threshold stress intensity factor by a nondestructive method. We observed a strong correlation between the increase in the volume fraction of the ?? phase and the decrease of ??K_th. Ultrasonic velocity increased in response to the coarsening behavior of the ?? phase in the vicinity of the grain boundaries.     

双相不锈钢复合钢板焊接

对双相不锈钢复合钢板的焊接特点、焊接材料、焊接方法与焊后热处理进行了重点分析与讨论     

High resolution imaging properties of the stem

The effect of the finite size of the atom on the resolution of the STEM is investigated. When the probe size becomes comparable to the size of the atom, the quality of the image depends on the scattering properties of the atom as well as the distribution of electrons in the probe. A technique for calculating the image of a single atom is developed by expanding the scattering amplitude. This allows the image of an atom or its spatial frequency to be expanded into various components. The specific case of dark field contrast formed with elastically scattered electrons is considered. The coefficients of the components are evaluated for carbon and thorium using complex scattering amplitudes derived from relativistic Hartree-Fock-Slater wavefunctions. The coefficients are evaluated for a 100 keV microscope using an immersion type objective lens whose aperture is limited to 12 mrad by primary spherical aberration and a 100 keV microscope using the same objective lens in conjunction with a corrector lens for spherical aberration. Secondary spherical aberration limits the objective aperture of the corrected microscope to 30 mrad.     

High resolution X-ray phase contrast synchrotron imaging of normal and ligation damaged rat sciatic nerves

This study was performed to apply synchrotron radiation (SR) imaging to a neuropathologic evaluation technique after treatment of peripheral nerve blocks. A phase contrast synchrotron images of normal and ligation damaged rat sciatic nerve were obtained with an 8 KeV monochromatic beam and 20-mum thick CsI(TI) scintillation crystal. The visual image was magnified using a 20x microscope objective and captured using an analog CCD camera. Obtained images were compared with conventional light microscopic findings from the same nerve samples. By using an edge enhancement effect of phase const with SR, we could easily discriminate each nerve fiber and identify the arrangement of nerve fibers within a whole thickness (about 1 mm in diameter) of peripheral nerve without sectioning and fixation. The composite SR image of a ligation damaged rat sciatic nerve sample showed that the response to nerve injury was different on each side of the site of injury. The SR image of damaged distal lesion showed destruction of neural microarchitecture and typical extensive Wallerian degeneration of nerve fibers as clearly as histologic image. We could get very detailed morphologic data for Wallerian degeneration of nerve fibers by using the SR imaging technique. We believe that the phase contrast synchrotron imaging has great potential as an imaging tool in the bioscience and medical science.     

Assessment of the high-temperature crack behavior for a 316L stainless steel structure with defects

An assessment of creep-fatigue crack initiation and growth for a 316L stainless steel structure has been carried out according to the current (2007 edition) and previous (2002 edition) versions of the French RCC-MR A16 procedure. Some significant changes have been made in terms of the formulae and material properties, which may cause big differences in the assessment. In this study, the changes in the A16 guide have been quantified for a 316L austenitic stainless steel structure, and the assessment results were compared with those of the observed images from a structural test for a welded component.     

双相不锈钢00Cr22Ni5Mo3N缸套制造工艺

介绍特种发动机的双相不锈钢00Cr22N i5Mo3N缸套的制造工艺分析研究,解决缸套制造的三个工艺难点:确定缸套离子氮化后的内孔最大变形量mδax;最大变形量mδax给磨削加工带来的影响;缸套外圆、内孔同轴度/圆柱度及表面粗糙度的控制。     

High resolution imaging by 1 MV electron microscopy

High voltage electron microscopy is well suited to the high resolution imaging of local structural changes in a material. New information at atomic resolution can be obtained on a broad range of material problems. Investigations of the structure of dislocations and planar faults in metallic and covalent crystals is presented.     

High resolution SEM imaging of gold nanoparticles in cells and tissues

The growing demand of gold nanoparticles in medical applications increases the need for simple and efficient characterization methods of the interaction between the nanoparticles and biological systems. Due to its nanometre resolution, modern scanning electron microscopy (SEM) offers straightforward visualization of metallic nanoparticles down to a few nanometre size, almost without any special preparation step. However, visualization of biological materials in SEM requires complicated preparation procedure, which is typically finished by metal coating needed to decrease charging artefacts and quick radiation damage of biomaterials in the course of SEM imaging. The finest conductive metal coating available is usually composed of a few nanometre size clusters, which are almost identical to the metal nanoparticles employed in medical applications. Therefore, SEM monitoring of metal nanoparticles within cells and tissues is incompatible with the conventional preparation methods. In this work, we show that charging artefacts related to non‐conductive biological specimen can be successfully eliminated by placing the uncoated biological sample on a conductive substrate. By growing the cells on glass pre‐coated with a chromium layer, we were able to observe the uptake of 10 nm gold nanoparticles inside uncoated and unstained macrophages and keratinocytes cells. Imaging in back scattered electrons allowed observation of gold nanoparticles located inside the cells, while imaging in secondary electron gave information on gold nanoparticles located on the surface of the cells. By mounting a skin cross‐section on an improved conductive holder, consisting of a silicon substrate coated with copper, we were able to observe penetration of gold nanoparticles of only 5 nm size through the skin barrier in an uncoated skin tissue. The described method offers a convenient modification in preparation procedure for biological samples to be analyzed in SEM. The method provides high conductivity without application of surface coating and requires less time and a reduced use of toxic chemicals.     

Ion beam detection of the austenitic-martensitic phase transformation of single crystal stainless steel

The austenitic-martensitic phase transformation in single crystal stainless steel of composition 70% Fe, Cr, 13% Ni has been observed by ion beam analysis techniques to occur at 175 K.     

Near-field Raman imaging of morphological and chemical defects in organic crystals with subdiffraction resolution

In this study we report on the application of an aperture near‐field optical microscope for Raman imaging of organic materials. Spectral analysis and detailed Raman imaging are performed with integration times of 100 ms per point, without the aid of field enhancement effects. The studied samples consist of two high Raman‐efficiency molecular samples: a 7,7′,8,8′‐tetracyanoquinodimethane crystal showing surface defects and a 7,7′,8,8′‐tetracyanoquinodimethane thin film characterized by the presence of submicrometre‐sized organometallic copper–salt complexes. In the first case, the effect of the surface deformation was studied, whereas in the second sample we were able to chemically image the formation of salt complexes. Subdiffraction resolution was achieved in both studies.     

High resolution imaging of surface patterns of single bacterial cells

We systematically studied the origin of surface patterns observed on single Sinorhizobium meliloti bacterial cells by comparing the complementary techniques atomic force microscopy (AFM) and scanning electron microscopy (SEM). Conditions ranged from living bacteria in liquid to fixed bacteria in high vacuum. Stepwise, we applied different sample modifications (fixation, drying, metal coating, etc.) and characterized the observed surface patterns. A detailed analysis revealed that the surface structure with wrinkled protrusions in SEM images were not generated de novo but most likely evolved from similar and naturally present structures on the surface of living bacteria. The influence of osmotic stress to the surface structure of living cells was evaluated and also the contribution of exopolysaccharide and lipopolysaccharide (LPS) by imaging two mutant strains of the bacterium under native conditions. AFM images of living bacteria in culture medium exhibited surface structures of the size of single proteins emphasizing the usefulness of AFM for high resolution cell imaging.     

Hydrogen embrittlement of a stainless ball bearing steel

Ball bearing steels are susceptible to hydrogen embrittlement caused by lubricant degradation. It has been shown that hydrogen embrittlement of 440C stainless steels is associated with the existence of M₇C₃ carbides. The behaviour of M₇C₃ carbides during hydrogen embrittlement was investigated by classical rotating beam fatigue and tensile tests of specimens into which hydrogen had been introduced by cathodic charging. The effects of the current density, the time and the stress of charging and the relaxation time between charging and mechanical testing were assessed. The hydrogen embrittlement was characterized by using tritiated water. High resolution autoradiography and scanning electron microscopy were used to determine the location of the hydrogen in the martensitic matrix relative to the M₇C₃ carbides and to the interfaces between the M₇C₃ carbides and small M₂₃C₆ carbides.     

High resolution electron microscopy of partial dislocations in the Laves phase structure

A Mg-base Laves phase was investigated by high resolution electron microscopy (HREM). Linear defects found at terminations of stacking faults were classified into three groups. The first is a partial dislocation at a termination of a stacking fault, the second is a superposed partial dislocation which is defined as a defect produced by a superposition of terminations of two or more stacking faults lying on neighbouring layers, and the third is a combined linear defect which consists of a characteristic combination of terminations of stacking faults. In the last case the total stacking fault vector becomes equal to the translation vector in the basal plane, so that the defect needs no relaxation of the lattice. The Burgers vectors of the partial dislocations were estimated with the aid of modified Burgers circuits.     

酸性介质中双相不锈钢与铁素体不锈钢的应力腐蚀研究

采用慢应变速率拉伸试验(SSRT)、扫描电镜(SEM)断口分析以及金相显微组织分析等方法对TP405铁素体不锈钢及2205双相不锈钢在酸性介质中应力腐蚀开裂(PSCC)行为进行了研究.并评定铁素体不锈钢与双相不锈钢在酸性介质中应力腐蚀开裂的敏感性.为在酸性介质中选择容器用钢提供依据.结果表明,拉伸试样全部断裂在焊缝或热影响区.试样断口形貌呈准解理断裂和韧性断裂.2205双相不锈钢的应力腐蚀敏感性比TP405铁素体不锈钢低.     

基于半盲解卷积复原的高分辨率视网膜成像系统

为获得高分辨率视网膜图像,建立了基于自适应光学的视网膜成像系统,并以成像时获得的残余像差作为图像复原的估计参数,通过半盲解卷积进行图像复原以获得高质量图像.通过Hartmann-Shark波前传感器和微机械薄膜变形镜组成的自适应光学系统对活体人眼像差进行测量与校正,并在成像时记录系统残余像差,据此重建光学传递函数作为图像复原模型初始参数估计,对获得的视网膜图像进行条件约束迭代半盲解卷积复原,消除像差对成像质量的影响,从而得到高分辨率视网膜图像.实验表明,系统获得的图像经该方法处理后可获得较满意视网膜图像,图像质量提高近一倍,成像成功率由38％提高至78％,成像时间缩短为原来的1/7.该方法在满足使用要求的前提下有效缩短了校正时间,提高了成像的成功率,提升了系统的适用范围.     

基于相位相关技术的MEMS旋转角度的高分辨力测量方法

实现MEMS微结构周期运动过程中各个时刻的旋转角度及其动态特性参数的高分辨力测量, 为提高MEMS器件的性能和可靠性分析提供重要参考。针对频闪成像技术获得的微结构运动图像序列,提出了一种基于相位相关技术与Radon变换技术相结合的旋转角度测量方法。该方法通过Radon变换将图像的空间坐标转换为极坐标的参数空间,使得空间坐标的旋转投影为参数坐标得平移运动,再通过相位相关技术的亚像素运动估计算法,可得到物体旋转角度的高分辨力测量结果。实验结果表明,该方法旋转角度测分辨力优于0.01°。该方法可以有效的减少由于旋转产生形变对测量结果的影响,提高测量结果的稳定性和减少测量误差。