【作者】 马靳河；

【导师】 卫英慧；

【作者基本信息】 太原理工大学 ， 材料加工工程， 2007， 硕士

【摘要】 近年来表面机械研磨处理(SMAT)方法作为制备纳米晶块体材料的一种方式受到了材料科学家们的广泛关注，这是因为由SMAT制备出的纳米结构表层无污染，无孔隙，材料的纳米化过程是在高的应变速率下通过强烈塑性变形来实现的。本文利用SMAT方法在纯铁及35CrMo表面获得了一定厚度的纳米结构表层，在纯铁与35CrMo钢表面形成的纳米晶粒平均大小分别约为10nm与15nm。为了探讨原子在纳米晶结构组织中的扩散行为，随后对SMAT前后的样品分别进行了气体渗氮、离子渗氮；采用电镀技术对纯铁样品表面进行了电镀镍处理；并运用离子注入技术对SMAT前后的纯铁样品分别进行了钛离子注入。通过金相显微镜、X射线衍射、透射电子显微镜、显微硬度测试仪对SMAT后样品的微观组织结构以及渗氮处理后样品的结构和性能进行了表征：通过辉光放电光谱仪测量了渗氮后氮的浓度随深度的变化：采用扫描电子显微镜分析了镍原子在纳米晶铁中的扩散行为；利用俄歇电子能谱仪分析了离子注入后钛的浓度随深度的变化情况。实验结果表明：1．SMAT后，在纯铁与35CrMo表面形成了晶粒取向呈随机分布的等轴状纳米晶组织。由SMAT引起的强烈塑性变形在样品表面随机发生，并且随着深度的增加强烈塑性变形量逐渐地减小，从而使得样品的微观结构组织也随着距离样品表面深度的增大而呈现出梯度变化。2．SMAT后样品表面层的显微硬度明显增大，表面纳米层的显微硬度约为心部基体硬度的两倍以上，并且随着深度的增大显微硬度值逐渐减小。极化腐蚀实验结果表明，SMAT方法所获得的纳米结构表层可以提高材料的耐腐蚀性能。3．SMAT前后的样品分别进行渗氮后，SMAT后样品的显微硬度略高于粗晶样品渗氮后的硬度值，并且氮原子在SMAT样品中的扩散深度大于在粗晶样品中的扩散深度，这是由纳米晶铁中大量晶界处较高的非均匀形核率所造成的。4．对SMAT前后的纯铁样品电镀镍后分别进行扩散退火处理，在300℃下，SMAT样品中就有明显的扩散现象产生，而对于粗晶样品，在500℃下扩散现象并不明显。由于SMAT样品中含有大量的非平衡缺陷与三叉晶界，所以镍原子在SMAT样品中更容易扩散。5．SMAT前后的纯铁样品分别经离子注入钛后，钛的浓度分布均呈Gauss分布，SMAT样品内部钛原子的浓度比粗晶样品内钛原子的浓度有所提高，但是两种样品的离子注入深度基本相同。更多还原

【Abstract】 In recent years, because surface mechanical attrition treatment (SMAT)enables the fabrication of a porosity-free and contamination-freenanocrystalline surface layer which is induced by the severe plasticdeformation at very high rates, the method of SMAT, which is used tofabricate bulk nanostructured materials (NSM), has attracted the growinginterest of specialists in materials science.In this paper, the nanostructured surface layer is obtained on a pure ironplate and a 35CrMo steel plate by using SMAT. The average grain size of thenanocrystallites approximates to 10nm and 15nm in the surface layers of pureiron and 35CrMo steel, respectively. In order to investigate the effect ofnanocrystallite on atomic diffusion kinetics, the gas nitriding and plasmanitriding for both the original coarse-grained samples and the SMAT samplesare carded out. The iron samples surface is cleaned and electroplated with alayer of pure nickel (Ni, about 5μm in thickness). Titanium (Ti) ions are implanted into the surface layers of the iron samples. Microstructure featuresof various sections in the surface layer and properties of the SMAT samplesare systematically characterized by using optical microscope, X-raydiffraction (XRD), transmission electron microscope (TEM), microhardnesstesting machine. The nitrided samples are also characterized and theconcentration of nitrogen (N) is measured along the depth after gas nitridingand plasma nitriding by means of Glow discharge spectroscopy (GDS).Scanning electron microscope (SEM) is used as analyzing diffusion behaviorof Ni atoms in the pure iron. Ti distribution is measured by making use ofAuger electron spectroscopy (AES). It shows that:1. Equiaxed nanocrystallites with random crystallographic orientationsare formed in the top surface layer of the iron and 35CrMo plates. DuringSMAT, severe plastic deformation occurs randomly in the surface layer, anddecreases gradually along the depth of the treated samples, which results inthe gradient variation of the microstructure.2. The microhardness of the nanostructured surface layer is found to beobviously increased, and is twice more than that of the original sample. Themicrohardness decreases gradually to that of the matrix along the depth of theSMAT sample. The polarization curves show that the nanostructured surfacelayer can improve the corrosion resistance behavior of the samples.3. For both samples nitrided, it can be seen that microhardness of the SMAT sample nitrided is a little higher than that of the original coarse-grainedsample nitrided. And the diffusion depth of N atoms in the SMAT sample isenhanced with respect to that in the coarse-grained sample. This can beattributed to the much enhanced heterogeneous nucleation rate at numerousgrain boundaries in the nanocrystallization iron.4. The diffusion phenomenon of Ni atoms in the SMAT iron canobviously appears at 300~C after diffusion annealing, otherwise there ishardly diffusion of Ni atoms at 500~C in the coarse-grained sample. So thediffusion of Ni can be facilitated due to the non-equilibrium defects and grainboundaries of triple junctions.5. The distributions of Ti concentration after ion implantation in thecoarse-grained iron and SMAT iron agree with the Gaussian distribution.Compared with that in the coarse-grained sample, Ti concentration in theSMAT sample is enhanced, but the implantation depths of both are nodifferent.更多还原