表面纳米化铁基金属原子扩散行为和抗氧化性能研究

发布时间：2018-03-24 10:15

本文选题：铁基金属　切入点：高温氧化　出处：《太原理工大学》2017年博士论文

【摘要】：高温氧化会导致金属部件或装置使用性能下降、服役寿命缩短。金属材料的腐蚀一般都是从表面开始的,材料表面的结构和性能对材料整体性能的影响极其敏感。因此,优化金属材料表面的结构和性能将大大提高材料的整体性能。铁基金属表面纳米化后,表层晶粒细化至纳米级,晶界体积分数增加,这为元素的快速扩散提供了通道。本文将金属表面纳米化与合金化相结合,从微观角度研究表面纳米化对原子扩散行为的影响和材料组织结构的演化规律。深入认识纳米结构金属中溶质原子的传输行为,分析表面纳米化对金属高温氧化行为的影响规律,丰富金属材料的耐高温氧化理论。利用表面机械研磨技术(Surface Mechanical Attrition Treatment,SMAT)实现纯铁的表面纳米化,研究表面纳米化工艺参数与表面组织结构、性能之间的关系。纯铁经SMAT可实现表面自纳米化,最表面形成了等轴状的纳米晶结构组织,晶粒尺寸约为12 nm。表面纳米化纯铁的微观组织结构沿深度的增加呈梯度变化,可分为纳米结构区(0~15μm)、亚微米结构区(15~40μm)、微米结构区(40~60μm)以及基体,晶粒细化机制以位错分割为主。表面纳米化使表层显微硬度显著提高,并且沿厚度方向逐渐减小至稳定值,硬度的增大是晶粒细化与加工硬化共同作用的结果。SMAT所获得的纳米结构使耐腐蚀性下降,拉伸强度显著提高。研究了金属表面纳米化对原子扩散行为的影响。纯铁加镍粉经smat后可在纯铁表面形成约110μm厚的铁镍混合层,晶粒细化的同时大量的位错等缺陷形成。弹丸撞击形成的大量应变能也促进了ni的扩散,在合金表面形成feni固溶相,退火热处理可进一步促进ni的扩散。smat处理后的纯铁离子注入钛结果表明,smat可大幅提高表层钛原子的浓度,主要原因在于经过smat处理的试样表层含有更多的缺陷(过饱和空位,高密度位错,非平衡晶界等),溶质原子与这些缺陷的交互作用导致其固溶度的增加。采用融盐法对纯铁进行渗硅处理,发现smat可缩短渗硅时间,提高渗硅深度。金属表面纳米化可提高表层原子在金属中的扩散速度和浓度,将表面纳米化与化学处理相结合为提高金属的表面性能提供了一种有效途径。以表面纳米化前后410s、304、430等典型不锈钢材料为对象,利用sem、eds、xrd等手段,对其在高温环境下氧化过程中的元素扩散、氧化膜结构、氧化产物类型、腐蚀破坏机理等进行了研究。结果表明,氧化过程中不锈钢首先发生cr的选择性氧化,然后合金元素向外扩散,氧化膜由内向外厚度增加。温度和氧化气氛是影响不锈钢氧化速率的关键因素,高温下水蒸气会加速不锈钢的氧化速度,起到自催化作用。高温氧化过程可归纳如下:首先金属表面出现横向覆盖的致密薄膜,随氧化时间的延长,薄膜厚度逐渐增加,致密度降低,进而在氧化膜内出现裂纹,并使氧化膜分成内外两层,在内外氧化膜及氧化膜与基体间出现空洞,并最终使氧化膜从基体上整体或部分脱落。smat处理在不锈钢表面获得纳米晶组织,增加了表层晶界的体积分数,提高了氧化物的形核几率;变形层中大量的晶体缺陷为元素扩散提供了更多的通道,促进了Cr,Ni,Fe等元素的选择性氧化。在氧化初期氧化动力学曲线呈线性规律迅速增重,但达到钝化的时间短,氧化物膜致密,使得抗氧化性大大提高。纳米表层比粗晶表面更容易形成连续的氧化膜,该膜层的内应力小,韧性好,与基体的结合力强,在高温下稳定性好,这也是SMAT提高试样抗氧化性的原因之一。
[Abstract]:High temperature oxidation leads to the decrease of metal parts or equipment performance, shorten the service lifetime. The corrosion of metal materials are generally starts from the surface, is extremely sensitive to influence the structure and properties of the surface material on the overall performance of the material. Therefore, optimizing the structure and properties of metal material surface will greatly improve the overall performance of the materials. The surface of nano iron after metallization, the grain refinement to the nanometer level, the increase of the volume fraction of grain boundary, which provides a channel for the rapid diffusion of elements. In this paper, metal surface nanocrystallization and alloy combination, evolution from the perspective of micro effect of surface nanocrystallization on the diffusion behavior of the materials and the organizational structure of the in-depth understanding of solute transport. Atoms of nanostructured metals, analysis of influence of surface nanocrystallization on high temperature oxidation behavior of metals, high temperature oxidation theory rich metal materials. By surface mechanical attrition Technology (Surface Mechanical Attrition Treatment, SMAT) the surface of nano iron, study of surface nanocrystallization process parameters and surface structure, the relationship between the performance of the SMAT can be realized. The pure iron surface self nanocrystallization, the surface nanocrystalline structure of equiaxed grain size is about. The gradient change increases the microstructure of 12 nm. surface nanocrystallization iron along the depth, which can be divided into nano structure zone (0~15 m), sub micron structure zone (15~40 m), micron structure zone (40~60 m) and the matrix grain refinement mechanism dominated by dislocation segmentation. Surface nanocrystallization of the surface microstructure the hardness increases significantly, and along the thickness direction decreases to a stable value, the increase of hardness is nano structure interaction and grain refinement hardening results obtained.SMAT the corrosion resistance decreased tensile strength significantly. High. The metal effect of surface nanocrystallization on the diffusion behavior. With pure nickel powder by SMAT can be formed after about 110 m thick iron nickel mixed layer on the surface of pure iron, grain refinement and lots of defects such as dislocations formed. A strain formed projectile can also promote the spread of Ni. The formation of FeNi solid solution phase on the surface of alloy, annealing treatment can further promote the iron ion diffusion.Smat Ni after implantation of titanium. The results showed that SMAT can significantly increase the concentration of the surface of the titanium atoms, the main reason is that the surface of the specimen after SMAT treatment with more defects (vacancies, high dislocation density, non equilibrium grain boundary), interaction of solute atoms and these defects lead to the solid solubility increases. The molten salt method of pure iron were siliconizing, found that SMAT can shorten the time of silicon infiltration, improve silicon infiltration depth. Metal surface nanocrystallization can be improved The surface atoms in the metal diffusion velocity and concentration, the surface nanocrystallization and chemical treatment combination provides an effective way to improve the surface properties of the metal. Before and after surface nanocrystallization of 410S, 304430 typical stainless steel as the object, using SEM, EDS, XRD and other means of the element diffusion, oxidation in the process of high temperature oxide film structure, oxidation product type, corrosion failure mechanism were studied. The results show that the selective oxidation of the oxidation process of Cr stainless steel at first, then the outward diffusion of the alloying elements, the film thickness increases from inside to outside. The temperature and oxidizing atmosphere are key factors affecting the oxidation rate of stainless steel, high temperature water vapor will accelerate the oxidation rate of stainless steel, to self catalysis. The high temperature oxidation process can be summarized as follows: the first thin film lateral covering the metal surface with oxidation The extension of the film thickness increases, the density decreased, and the cracks in the oxide film, and the film is divided into two outer layers, there are holes in inner and outer oxide film and oxide film and the substrate, and eventually make the whole film from the substrate or partially exfoliated.Smat processing to obtain nanocrystalline microstructure on the surface of stainless steel, increases the volume fraction the surface of the grain boundary, improved oxide nucleation probability; deformation of large crystals of the defect layer provides more channels for promoting the diffusion of elements Cr, Ni, selective oxidation of Fe elements. In the early stage of oxidation the oxidation kinetics curve linearly increases rapidly, but reached the passivation time short, oxide film dense, xidant is greatly increased. The surface layer is easier to form a continuous film than the coarse surface, the internal stress of the film, good toughness, and matrix adhesion strong, under high temperature stability Well, it is also one of the reasons that SMAT improves the antioxidant properties of the sample.

【学位授予单位】：太原理工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG178

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