棘爪杆断裂的失效分析

在核电机组的数十年寿期内需要定期从反应堆中取出乏燃料并装入新燃料，这一般是在大修期间通过反应堆的燃料装卸贮存系统进行的。在燃料装卸贮存系统中，棘爪是其吊装工具的起制动作用的零件，由于燃料组件在吊装过程中要随时调整位置，这使得棘爪杆在吊装工作时会反复受到制动弯矩的作用。     

18Cr2Ni4WA材料时效脆化评价及改进措施研究

为消除 1 8Cr2Ni4WA材料的时效脆化因素 ,对原材料在不同条件下进行了热处理 ,并对热处理前后的试样在 3 0 0或 3 5 0℃下进行时效考验 ,通过测定硬度和冲击韧性来评价它们的强韧性 ,并利用扫描电镜分析显微组织和冲击断口特征。结果表明 :原 1 8Cr2Ni4WA材料中存在残余奥氏体不稳定相 ,有时效脆化倾向。通过合理的热处理 ,可消除材料中的残余奥氏体不稳定相 ,达到防止时效脆化的目的     

A508-3钢临界温度A_(C1)的电镜测定

利用透射电镜技术测定了 A5 0 8- 3钢的临界温度 AC1,测定结果比膨胀仪法的结果低 2 5℃左右。原因是电镜技术可以发现极微小区域中发生的相变以及它更接近于平衡状态。最后还结合热处理实际讨论了该结果在质量保证中的作用。     

表面改性氮化钛薄层的电子衍射分析

近年来离子注入作为表面改性的有效方法得到了快速的发展,氮化钛具有很高的硬度,在材料表面形成的薄层氮化钛可以提高抗磨损性能,这使得氮离子注入受到工程界的重视。改性薄层的研究还能丰富金属物理及金属学的知识,所以也引起了科学界的兴趣。本工作对离子束强化沉积得到的表面改性氮化钛薄层作了透射电镜观察,着重分析了其电子衍射强度异常现象。     

A5O8-3钢热处理后的显微组织

利用光镜和电镜研究了热处理后 A508-3钢的各种显微组织。结果表明:在中等冷却速度(70—480℃/min)下组织为粒状贝氏体,经长时间高温回火后,不仅小岛发生分解,基体上还均匀析出合金碳化物 Mo_2C,这对钢的强韧性产生不利影响,为此,加入少量的铌是有利的。     

Synthesis and characterization of single-crystal strontium hexaboride nanowires

Catalyst-assisted growth of single-crystal strontium hexaboride (SrB6) nanowires was achieved by pyrolysis of diborane (B2H6) over SrO powders at 760-800 degrees C and 400 mTorr in a quartz tube furnace. Raman spectra demonstrate that the nanowires are SrB6, and transmission electron microscopy along with selected area diffraction indicate that the nanowires consist of single crystals with a preferred [001] growth direction. Electron energy loss data combined with the TEM images indicate that the nanowires consist of crystalline SrB 6 cores with a thin (1 to 2 nm) amorphous oxide shell. The nanowires have diameters of 10-50 nm and lengths of 1-10 microm.     

Dielectrophoretic deposition of graphite oxide soot particles

Alternating current dielectrophoresis in water was used to position graphite oxide soot (GO-soot) particles generated by rapid thermal expansion of graphite oxide under inert gas. The dielectrophoretic deposition was carried out at a frequency of 10 MHz and a peak-to-peak voltage of 10 V, and the deposited particles were analyzed using scanning electron microscopy. The vertical cross section, obtained by focused ion beam cutting, shows the wrinkled layers of the GO-soot particles and cavities between the layers. The electrical transport measurements show typical characteristics of metal-like pathways. The improved electrical contact between electrodes and GO-soot, probably due to the thin platelet structure of GO-soot, makes the material favorable for electrical device applications. The results demonstrate that AC dielectrophoresis can be used to selectively deposit graphite oxide soot particles at desired locations.     

Bond-detach lithography: a method for micro/nanolithography by precision PDMS patterning

We have discovered a micro/nanopatterning technique based on the patterning of a PDMS membrane/film, which involves bonding a PDMS structure/stamp (that has the desired patterns) to a PDMS film. The technique, which we call "bond-detach lithography", was demonstrated (in conjunction with other microfabrication techniques) by transferring several micro- and nanoscale patterns onto a variety of substrates. Bond-detach lithography is a parallel process technique in which a master mold can be used many times, and is particularly simple and inexpensive.     

Graphene films with large domain size by a two-step chemical vapor deposition process

The fundamental properties of graphene are making it an attractive material for a wide variety of applications. Various techniques have been developed to produce graphene and recently we discovered the synthesis of large area graphene by chemical vapor deposition (CVD) of methane on Cu foils. We also showed that graphene growth on Cu is a surface-mediated process and the films were polycrystalline with domains having an area of tens of square micrometers. In this paper, we report on the effect of growth parameters such as temperature, and methane flow rate and partial pressure on the growth rate, domain size, and surface coverage of graphene as determined by Raman spectroscopy, and transmission and scanning electron microscopy. On the basis of the results, we developed a two-step CVD process to synthesize graphene films with domains having an area of hundreds of square micrometers. Scanning electron microscopy and Raman spectroscopy clearly show an increase in domain size by changing the growth parameters. Transmission electron microscopy further shows that the domains are crystallographically rotated with respect to each other with a range of angles from about 13 to nearly 30°. Electrical transport measurements performed on back-gated FETs show that overall films with larger domains tend to have higher carrier mobility up to about 16,000 cm(2) V(-1) s(-1) at room temperature.     

Synthesis and characterization of large-area graphene and graphite films on commercial Cu-Ni alloy foils

Controlling the thickness and uniformity during growth of multilayer graphene is an important goal. Here we report the synthesis of large-area monolayer and multilayer, particularly bilayer, graphene films on Cu-Ni alloy foils by chemical vapor deposition with methane and hydrogen gas as precursors. The dependence of the initial stages of graphene growth rate on the substrate grain orientation was observed for the first time by electron backscattered diffraction and scanning electron microscopy. The thickness and quality of the graphene and graphite films obtained on such Cu-Ni alloy foils could be controlled by varying the deposition temperature and cooling rate and were studied by optical microscopy, scanning electron microscopy, atomic force microscopy, and micro-Raman imaging spectroscopy. The optical and electrical properties of the graphene and graphite films were studied as a function of thickness.