共查询到18条相似文献,搜索用时 358 毫秒
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将初始组织状态相同、表面粗糙度R_a为0. 1μm的40CrNiMo试样,分别放置在距阳极不同距离的碳钢圆筒内外进行离子渗氮。随后利用光学显微镜、显微硬度计和三维表面形貌测量系统测定渗氮后各试样的表面硬度、渗层深度、显微组织及表面粗糙度。结果发现:各试样的表面硬度和渗层深度无明显差别,渗氮层显微组织也无明显区别。但渗氮后各试样表面粗糙度却有较明显的差别:当试样放置在圆筒外,距离阳极越远表面粗糙度越高;距阳极距离相同时,置于碳钢圆筒中的试样的表面粗糙度比置于筒外的试样小的多。渗氮层表面粗糙度的降低有利于降低零件的缺口敏感性,提高零件的疲劳性能。 相似文献
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The active screen plasma and DC plasma nitriding of the low alloy steel 722M24 are investigated. Experimental results showed that the metallurgical characteristics and hardening effect on 722M24 steel nitrided by AS plasma nitriding at both floating potential and grounded potential were similar to those nitrided by DC plasma nitriding. Particles sputtered from the active screen and deposited on the specimen surface play the role of the nitrogen carrier in AS plasma nitriding. XRD and high-resolution SEM analysis indicated that the particles with sizes in sub-micron scale were FexN (x > 2). Based on metallurgical analysis and Optical Emission Spectrometer (OES) experimental results, an AS plasma nitriding model has been proposed considering that AS plasma nitriding is a multi-stage process, involving sputtering, physical adsorption, desorption, diffusion and deposition. 相似文献
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ZhaoCheng C.X.Li H.Dong T.Bell 《材料热处理学报》2004,25(5):330-333
Active screen plasma nitriding (ASPN) is a novel nitriding process, which overcomes many of the practical problems associated with the conventional DC plasma nitriding (DCPN). Experimental results showed that the metallurgical characteristics and hardening effect of 722M24 steel nitrided by ASPN at both floating potential and anodic (zero) potential were similar to those nitrided by DCPN. XRD and high-resolution SEM analysis indicated that iron nitride particles with sizes in sub-micron scale were deposited on the specimen surface in AS plasma nitriding. These indicate that the neutral iron nitride particles, which are sputtered from the active screen and transferred through plasma to specimen surface, are considered to be the dominant nitrogen carder in ASPN. The OES results show that NH could not be a critical species in plasma nitriding. 相似文献
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材料的活性屏等离子渗氮 总被引:1,自引:0,他引:1
近年来,等离子渗氮技术的迅速发展和在表面工程领域的应用呈现出减缓的趋势,其原因是传统的直流等离子体技术存在一些固有的缺点,例如,炉温难以保持均匀,等离子体不够稳定以及因打弧而引起工件表面损伤等。克服这些不足之处的努力促使了活性屏等离子渗氮(ASPN)技术的发展。本文从技术和环境优势角度证明,ASPN可以应用于低合金钢、工具钢、不锈钢以及能进行传统直流等离子渗氮的其他钢种。此外,ASPN可以处理不适合直流等离子渗氮的非导电材料,如经氧化处理的钢和高分子材料。从长远看,对环境友好且技术先进的等离子渗氮比传统的盐浴和气体渗氮更有优势。活性屏等离子渗氮技术是充分发挥等离子体技术在化学热处理及有关表面工程中应用潜力的新方法。 相似文献
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《International Heat Treatment & Surface Engineering》2013,7(1):19-23
AbstractActive screen plasma nitriding (ASPN) is commonly used when regular surface hardening is necessary. The ASPN technique produces a more homogeneous surface coating than direct current plasma nitriding (DCPN) due to different process principles. The term active screen in plasma nitriding refers to a cathodic cage with a defined geometry. The purpose of this work was to study the differences between ASPN using a hemispherical cathodic cage and ASPN using a normal cylindrical cathodic cage. Following some trials using similar parameters, the tests were carried out with three conditions: with DCPN, with a cylindrical cathodic cage in ASPN and with a hemispherical cathodic cage in ASPN. X-ray diffraction and scanning electron microscopy analysis together with energy dispersive spectroscopy were applied to characterise the nitrided layers. The nitrided layers are not the same for each of the conditions used. The ASPN with a hemispherical cathodic cage produced a layer of almost Fe3N alone, while the other processes gave significant amounts of Fe4N in the nitrided layer. Scanning electron microscopy analysis showed different surface morphology for each condition. 相似文献
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ZHENG Chuan-lin 《中国有色金属学会会刊》2004,14(Z1)
Ti-N graded ceramic layer was formed on titanium by using DC hollow-cathode plasma nitriding technique. The structure of Ti-N layer was analyzed using X-ray diffractometry(XRD) with Cu Kα radiation, and the microhardness( HV0.1) was measured from the surface to inner along the cross section of Ti-N layer. The results indicate that the Ti-N graded layer is composed of ε-Ti2 N, δ-TiN and α-Ti(N) phases. Mechanism discussion shows that hollow-cathode discharge can intensify gas ionization, increase current density and enhance the nitriding potential, which directly increases the thickness of the diffusion coatings compared with traditional nitriding methods. 相似文献
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为揭示活性屏等离子体源渗氮工艺特性(试样偏压电位和试样距屏高度)对AISI 316奥氏体不锈钢渗氮效果的影响规律,利用最小二乘法线性回归拟合了不同工艺条件下渗氮层厚度数据,绘制了活性屏等离子体源渗氮AISI 316奥氏体不锈钢的工艺特性图,以此确定其最佳工艺参数。并通过对金属网屏上溅射颗粒的化学成分和相结构分析,探讨了活性屏等离子体源渗氮的传质机制。结果表明:渗氮层厚度随试样距屏高度增大而降低,当适当降低渗氮气压或试样施加一定负偏压时,均有助于提高渗氮层的厚度,并且证实了"溅射-再沉积"模型是活性屏等离子体源渗氮重要的传质机制。 相似文献
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Active screen plasma nitriding (ASPN) was conceived in order to reduce negative effects observed in direct current plasma nitriding arising from the application of bias to the components. The mechanism of nitrogen mass transfer in ASPN is still not fully understood. Here, we compare the microstructure, composition and hardness response of AISI P20 and H13 steels after nitriding. A set of samples was nitrided with sample bias applied directly and another set was nitrided at floating potential under an active screen. Similar nitrogen content and hardness profiles were obtained for the samples treated using a bias and under an active screen separated from the samples by 12 mm. When the sample-screen separation was increased from 12 to 70 mm the hardness response improved. The principle processes occurring during ASPN are proposed based on the experimental results. In ASPN, a flux of energetic nitrogen species is generated by the active screen which, provided that the samples are within the range of the energetic species, bombards the surface of the samples being treated. This flux is critical in establishing a nitrogen potential and a satisfactory response in the components. 相似文献
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The nitriding of low alloy steel has been carried out at anodic potential in a space enclosed by an active screen that consists of two cylinders with different diameter. These two cylinders made up a hollow cathode in a discharge system. The difference in diameter of the two cylinders is about 8-10 mm to maintain strong discharge between them. They can also be heated rapidly to the required temperature for treatment. The sample to be nitrided was held at the same potential as that of the anode used in the discharge and heated through heat radiation from the hot cylinders and by electron bombardment. Electrons bombarded the surface of the sample even though the intensity of bombardment was low because of the anodic sheath. To illustrate the effect of the anodic potential on the nitriding a comparison was made between nitriding at anodic and cathodic potential (general plasma nitriding). The phase composition, the compound layer thickness and the surface topography of the nitrided layer, as well as its properties, were investigated using X-ray diffraction, scanning electron microscopy and microhardness tester. In particular, the corrosion properties of the untreated and plasma nitrided samples were evaluated using anodic polarization tests in 3.5% NaCl solution. The results showed that anodic plasma nitriding not only increased the surface hardness but also improved the corrosion resistance of the low alloy steel. 相似文献