【作者】 刘林飞；

【导师】 周上祺；

【作者基本信息】 重庆大学 ， 材料学， 2007， 博士

【摘要】 离子化学热处理由于能显著改善金属材料表面性能,得到了广泛的应用。但是目前离子渗氮生产和科研中主要使用氨气、氮气和氢气作为气源,存在氨气的污染、使用高压气瓶和氢气易燃易爆的安全隐患。众所周知,节能降耗和绿色热处理是当今热处理发展的必然趋势,离子渗氮和共渗工艺中的环保和安全问题同样值得关注。空气是大自然中取之不尽、用之不竭的零成本气源,而且不会造成环境污染。本文基于等离子体放电理论和低温化学热处理原理,研究了空气-有机液体离子氮碳氧共渗工艺和机理。为了研究空气-有机液体离子氮碳氧工艺,首先进行了氮气-甲烷离子氮碳工艺的基础研究,然后研究了空气-汽油和空气-乙醇离子氮碳氧共渗工艺。利用金相显微镜、扫描电镜、显微硬度计和X射线衍射仪等测试手段,研究了40Cr钢在不同电压和共渗介质条件下离子氮碳氧共渗后,其共渗层的显微组织、相组成和硬度梯度分布,并用磨损实验和电化学分析方法测定了共渗后的耐磨和耐腐蚀性能。理论分析和实验结果表明:(1)空气-有机液体离子氮碳氧共渗工艺是可行的。(2)氮气-甲烷离子氮碳共渗、空气-汽油和空气-乙醇离子氮碳氧共渗的渗层具有类似的显微组织和相结构,渗层由白亮层、扩散层和心部基体组织三部分组成,层深和相组成主要与介质种类、阴极电压和气体介质混合比有关。有利于介质离解产生活性氮原子的阴极电压和合适的气体混合比,有合适的氮、碳和氧浓度,将增加表面渗层中高氮的ε-Fe3N相的体积百分数,提高试样表面氮浓度和硬度。(3)采用氮气-甲烷离子氮碳共渗、空气-汽油和空气-乙醇离子氮碳氧共渗时,其共同点是必须产生活性氮原子,活性氮原子主要来自于甲烷、汽油和乙醇离解产生的H2+、H+等离子与N2中性分子的非弹性碰撞离解。(4)随着甲烷、汽油和乙醇流量比的增加,共渗效果先增强再减弱,分别在氮气-甲烷、空气-汽油和空气-乙醇流量比为25:3、25:2.5和25:6时共渗效果最好。过多的甲烷、汽油和乙醇流量将产生大量的活性C原子,过多的碳原子的渗入阻碍氮的扩散。(5)汽油和乙醇的氧化重整既能消耗氧气,降低氧偏压,又能产生氢离子,从而促进活性氮原子的产生。(6)阴极电压的增加,有利于提高电场能,促进活性原子的产生,但是过高的阴极电压对应炉内气压低,使活性原子的浓度减少。氮气-甲烷离子氮碳共渗和空气-乙醇离子氮碳氧共渗在电压分别为600V和640V时共渗效果最好。采用第一性原理研究了C、N、O在Fe(111)表面上不同覆盖度时的吸附,Fe-C(N、O)体系的化合物和固溶体的形成能,以及C、N、O在铁中的扩散激活能和空位形成能。计算结果表明:(1)C、N和O在Fe(111)表面上都是强化学吸附,O在低覆盖度下容易吸附,而C、N在比较宽的覆盖度范围内都容易吸附。(2)铁的碳化物最容易形成,Fe3N也比较容易生成,其次为Fe4N、FeN和Fe2N,随N含量增加,形成能降低。奥氏体的含氮固溶体比铁素体的含氮固溶体容易形成。(3)Fe2-3(C、N)比Fe2-3N的形成能低,少量的C能促进氮化物的形成。(4)C、N和O容易在铁的八面体间隙聚集和扩散,C、N、O三元素中,N的扩散激活能最小,过量C的渗入使N的扩散激活能增加。空气-有机液体离子氮碳氧共渗工艺包括活性原子的产生、原子与表面的反应和原子向试样内部扩散三个互相制约、紧密联系的过程。其中活性原子的产生是控制步骤。本文提出的空气-乙醇离子氮碳氧共渗工艺,具有推广应用价值。更多还原

【Abstract】 The ion chemical heat treatment has been applied extensively because it can improve the surface of metal materials performance remarkably. But currently, the pure NH3 or N2-H2 mixtures has been adopted for the production and study, there have been some hidden troubles in nitriding heat process because NH3 can pollute the environment and the used high-pressure bottle and H2 gas exist safety hidden troubles. As is well known, the saving energy and reducing wastage“green heat treatment”are developing tendency in nowadays. The environmental protection and safe problems of media in ion nitriding and multi-element penetration processes are deserved alike.The air is zero costs gas source. There is no ways more than enough to go around in nature, and more it will not result in the pollution of the environment. In this disseratation, the process and mechanism of ion N-C-O multi-element penetration in an atmosphere of air and organic liquid are studied according to the discharge theory of plasma and principle of chemical heat treatment in low temperature. In order to prepare the basic study on ion N-C-O multi-element penetration in an atmosphere of air and organic liquid, the ion nitrocarburizing of nitrogen and methane is carried out. Then the ion N-C-O multi-element penetration in an atmosphere of air and gasoline or ethanol is designed and studied. The microstructure, phase composition and hardness gradient distribution of multi-element penetrating layers of 40Cr steel which were ion N-C-O multi-element penetrated in different voltage and media have been researched by some test methods such as Microhardness apparatus, Microcopy and X-ray diffractometer etc. what’s more the abrasion and causticity of samples which were ion multi-element penetrated are mensurated by wearing test and electrochemical analysis.The theoretical analysis and experimental results show that: (1) The ion N-C-O multi-element penetration process in an atmosphere of air and organic liquid is feasible. (2) There are similar microstructures and phase compositions in the penetrating layers of the samples which were nitrocarburized in an atmosphere of nitrogen and methane, ion N-C-O multi-element penetrated in an atmosphere of air and gasoline or ethanol. The penetrating layers are composed of light layer, diffusion layer and basis. And the penetrating layer depth and phase compositions relate with media species, cathode voltage and mixture ratio of gases. The parameter matches of cathode voltage and mixture ratio of gases that benefiting to media dissociated to yield active nitrogen atoms will increase the volume percent ofε-Fe3N phase with high nitrogen content in the penetrating layers, the proper nitrogen, carbon and oxygen contents enhance their surface hardness. (3) The common speciality is existing active nitrogen atom which mostly comes from the ionization of nitrogen molecule because of non-elastically collision between the H2+、H+ion produced by methane, gasoline and ethanol and the neutral nitrogen molecule in nitrocarburizing in an atmosphere of nitrogen and methane and ion N-C-O multi-element penetration in an atmosphere air and gasoline or ethanol. (4) With the increment of ratio of methane, gasoline and ethanol, the multi-element penetration effect existes a maximum. The effect is best when the ratio of nitrogen and methane, air and gasoline, air and ethanol is 25:3, 25:2.5 and 25:6 respectively. The overfull flux of methane, gasoline and ethanol will produce quantities active carbon atoms which baffle the diffusion of nitrogen atom. (5) In plasma gasoline and ethanol oxidation reforming reaction takes place. On the one hand it decreases oxygen press. On the other hand, it can produce hydrogen which can promote the production of active nitrogen. (6) The increment of cathode voltage is propitious to increase electric field energy which facilitates the production of active atoms. But the exorbitant cathode voltage with correspond lower gas pressure reduces the content of active atoms. There are best effects when the cathode voltages are 600V and 640V respectively in nitrocarburizing in nitrogen and methane and ion N-C-O multi-element penetration in air and ethanol.A study of C、N、O adsorption on the Fe(111) surface at different coverage , the formation energy of compound and solid solutions in the Fe-C(N、O) system and the diffusion of C、N、O in theα-Fe are carried out with the first principles calculation. The calculation results show that: (1) C、N、O adsorption on the Fe(111) are strong chemical adsorption. O adsorption is easy at the low coverage, while N and C with wider coverage scope. (2) The carbide of iron forms the most easily, then are Fe3N、Fe4N、FeN and Fe2N. With the increase of nitrogen content, the formation energy decreases. The formation of solid solution with nitrogen in austenitic is easier than in ferrite. (3) The formation energy of Fe2-3(C、N) is lower than that of Fe2-3N. A few of carbon can promote the formation of nitride. (4) C、N and O assemble and diffuse in octahedral clearance of iron easily. The diffusion activation energy of N among C、N and O is the smallest, and superfluous carbon will result in the increase of the diffusion activation energy of N.Ion N-C-O penetration process in air-organic liquid comprises three courses which are condition of each other and close interaction: the production of active atoms, the reactions of atoms with the surface and the diffusion of atom in sample. Among them, the production of active atom is manipulative step. The ion N-C-O multi-element penetration process presented in this thesis posses wide application value.更多还原