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A. Buchwalder R. Zenker K. Fritzsch K. Rüthrich K. Nagel W. Griesbach 《Materialwissenschaft und Werkstofftechnik》2015,46(6):550-562
Die typischen hohen C‐ und Si‐Gehalte von Gusseisenwerkstoffen und der weiche Graphit limitieren die Behandel‐ und Beanspruchbarkeit nach dem Nitrieren und der Hartstoffbeschichtung. Wenn die Gusseisenoberfläche vor den genannten Randschichtbehandlungen mittels Elektronstrahls umgeschmolzen wird (Kombinationsbehandlung) und eine harte, graphitfreie ledeburitische Randschicht gebildet wird, dient diese als Stützschicht für die harte und dünne Verbindungs‐ bzw. Hartstoffschicht. Vergleichende Verschleißtests (Stift‐Scheibe) zeigten, dass bei geringen Lasten die Verschleißrate aller Einzel‐ und Kombinationsbehandlungen auf einem vergleichbar niedrigen Niveau wie der unbehandelte und beschichtete Grundwerkstoff liegen. Bei höheren Lasten kommt das überragende Verschleißverhalten der Kombinationsbehandlungen gegenüber den Einzelbehandlungen voll zum Tragen. Die Bildung defektfreier Randschichten nach der Kombinationsbehandlung resultiert außerdem in einer deutlichen Verbesserung der Korrosionsbeständigkeit in chloridhaltiger Lösung. Im Vergleich zum Grundwerkstoff und den Einzelbehandlungen wurden die relevanten Potenziale zu deutlich positiveren Werten verschoben. 相似文献
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A. Buchwalder J. Thronicke A. Jung P. Hengst R. Hunger S. Hartwig R. Zenker 《Materialwissenschaft und Werkstofftechnik》2021,52(8):815-830
Boriding produce thick hard layers on cast iron components, which can improve their wear and corrosion behaviour. However, this potential cannot be fully exploited by a simple boriding due to the material specific presence of graphite. In that context, this paper presents results of two fundamentally different electron beam liquid surface treatments (remelting, cladding with nickel-based additive) and their possibilities and limitations regarding subsequent boriding. The boriding behaviour under conventional high temperatures (760 °C–860 °C), and experiments on low-temperature boriding (600 °C–700 °C) were investigated. Under identical treatment conditions, the compound layer thicknesses generated on the unalloyed surfaces (remelting) were approx. 50 %–75 % greater than those of the alloyed surfaces (cladding). A two-layered boride layer structure were generated, though with different phase compositions. Nevertheless, the hardness of all borided layers were comparable. Surface hardness measurements revealed that the supporting effect of substrates plays a decisive role up to a boride layer thickness of approx. 57 μm. In this layer-thickness range, the compound hardness of the alloyed substrates is higher than that of the unalloyed substrates. This knowledge should prove decisive for the selection of layer composites for corrosive and/or tribologically stressed components. 相似文献
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A. Buchwalder J. Thronicke A. Holst P. Hollmann P. Hengst R. Zenker 《Materialwissenschaft und Werkstofftechnik》2021,52(6):603-616
Surface treatments are frequently used to improve the wear and/or corrosion resistance of metal components. In the case of cast iron, the material-specific graphite limits both its treat-ability and load-bearing behaviour. A promising option for overcoming these limitations is provided by combination processes, in which near-surface graphite is first removed in an initial liquid-phase surface treatment – such as, e. g., remelting, alloying or cladding using electron beam (EB) – before application of thermochemical processes or hard coatings. A prerequisite for this is sufficient thermal resistance of these microstructures. This was investigated by means of annealing tests. The ranges of temperature used for annealing are based on those typically used for hard coating (250 °C–500 °C), nitriding (400 °C–600 °C) and boriding (600 °C–860 °C). The metastable microstructures produced as a result of rapid solidification during the electron beam liquid-phase treatments differ in their alloy content and, therefore, in their microstructural components. Hardness measurements after annealing provided an initial indication of thermal stability. Based on these measurements, interesting treatment conditions were analysed in more detail using scanning electron microscopy and x-ray diffraction. The focus of interest was on the formation of secondary graphite and the dissolution of ledeburitic carbides and other intermetallic phases. 相似文献
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聚乳酸纤维制备的研究进展 总被引：7，自引：0，他引：7
聚乳酸纤维是可生物降解的新型绿色纤维,它可由常见的纤维成型加工工艺--溶液纺丝和熔融纺丝制得.从原料预处理、工艺过程和影响熔纺纤维结构和性能的因素三方面详细地综述了适合工业化生产的熔融纺丝工艺,并简单介绍了在医药领域应用前景广阔的静电纺丝制备聚乳酸超细纤维的研究现状. 相似文献
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K. Neuking A. Abu‐Zarifa S. Youcheu‐Kemtchou G. Eggeler 《Advanced Engineering Materials》2005,7(11):1014-1023
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Y.‐G. Jiang C.‐R. Zhang F. Cao S.‐Q. Wang Y.‐B. Cao 《Advanced Engineering Materials》2007,9(10):921-924
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The corrosion behavior of spheroidal graphite and flake graphite cast irons was studied in oxidizing and sulfidizing atmospheres between 600 and 800℃ for 50 h. The corrosion rate in the sulfidizing atmosphere was faster than that in air above 700℃, due to the formation of the Fe0.975S sulfide. The corrosion rate of the spheroidal graphite cast iron was similar to that of the flake graphite cast iron. 相似文献
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碳纤维具有低密度、高模量等一系列优异性能,具有广泛的应用领域。木质素作为一种丰富的可再生资源在自然界中的含量仅次于纤维素,碳含量高达60%以上,是一种新型的制备碳纤维的理想原料。文中根据纺丝工艺的不同,从前驱体溶液、纺丝参数、预氧化和碳化工艺角度,分别阐述并讨论了木质素基碳纤维的多种制备方法,包括熔融纺丝、湿法纺丝、凝胶纺丝及静电纺丝。并介绍了木质素基碳纤维的应用领域,为今后研究者高效利用木质素资源提供参考。 相似文献
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Vladimir D Blank Boris A Kulnitskiy Igor A Perezhogin Yuriy L Alshevskiy Nikita V Kazennov 《Science and Technology of Advanced Materials》2009,10(1)
The effect of an electron beam on nanoparticles of two Fe carbide catalysts inside a carbon nanofiber was investigated in a transmission electron microscope. Electron beam exposure does not result in significant changes for cementite (θ-Fe3C). However, for Hägg carbide nanoparticles (χ-Fe5C2), explosive decay is observed after exposure for 5–10 s. This produces small particles of cementite and γ-Fe, each covered with a multilayer carbon shell, and significantly modifies the carbon-fiber structure. It is considered that the decomposition of Hägg carbide is mostly due to the damage induced by high-energy electron collisions with the crystal lattice, accompanied by the heating of the particle and by mechanical stress provided by the carbon layers of the nanofiber. 相似文献
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AbstractThe effect of an electron beam on nanoparticles of two Fe carbide catalysts inside a carbon nanofiber was investigated in a transmission electron microscope. Electron beam exposure does not result in significant changes for cementite (θ-Fe3C). However, for Hägg carbide nanoparticles (χ-Fe5C2), explosive decay is observed after exposure for 5–10 s. This produces small particles of cementite and γ-Fe, each covered with a multilayer carbon shell, and significantly modifies the carbon-fiber structure. It is considered that the decomposition of Hägg carbide is mostly due to the damage induced by high-energy electron collisions with the crystal lattice, accompanied by the heating of the particle and by mechanical stress provided by the carbon layers of the nanofiber. 相似文献
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Eugen Hegelmann Anne Jung Philipp Hengst Rolf Zenker Anja Buchwalder 《Advanced Engineering Materials》2018,20(9)
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H.‐J. Spies Ch. Eckstein H. Biermann A. Franke 《Materialwissenschaft und Werkstofftechnik》2010,41(3):133-141
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《Small Methods》2017,1(6)
Novel pathways to use a focused electron beam in ultrahigh vacuum in combination with catalytic growth protocols are explored for the fabrication of well‐defined nanostructures. Thereby, the basic process is the local deposition of material from different precursor molecules (Co(CO)3 NO, Fe(CO)5). This can be realized with a focused electron beam by direct deposition of the precursor or by a chemical modification of the substrate, such that it becomes activated toward the decomposition of the precursor. For both methods, autocatalytic growth (AG) processes can occur, yielding the deposition of additional material. Interestingly, significantly different chemical selectivities for the two precursors are found, which can drastically change upon subtle changes of the surface. It is demonstrated that AG can be tweaked by the choice of the substrate/precursor combination. One possibility to quench catalytic activity of a substrate is the preparation of a thin layer of organic molecules, here porphyrins, which enables the fabrication of hybrid metal–organic nanostructures with line widths below 20 nm. Based on these findings, corresponding techniques are developed which exploit (auto)catalytic effects for the controlled fabrication of nanostructures. These results indicate that every substrate is applicable to electron beam induced surface activation by preparation of a thin porphyrin layer. 相似文献