Fe-Cr合金溅射纳米晶薄膜腐蚀电化学行为的XPS及第一性原理计算的研究

发布时间：2018-11-20 09:18

【摘要】：磁控溅射不锈钢纳米晶薄膜具有比同成分粗晶材料更优异的耐腐蚀能力。前期研究发现材料表面纳米化会促进Cr在钝化膜内的富集,抑制Cl-的表面吸附,但对其中更微观、本质的作用机理尚不清楚。本论文以不锈钢的模型合金体系-Fe-Cr合金为研究对象,采用传统电化学测试手段、表面分析技术以及第一性原理计算相结合的方法,对溅射纳米晶薄膜材料的钝化、Cl-表面吸附及在钝化膜内的传输行为进行研究。深入探讨了纳米化对于Fe-Cr合金腐蚀行为的影响机制。ARXPS表面分析结果表明,粗晶Fe-20Cr合金及同成分溅射纳米晶薄膜在0.15 MB(OH)3+0.075M Na2B4O7·10H2O (pH8.6)缓冲溶液中表面形成的钝化膜均具有外层为氢氧化物的水合层和内层为氧化物层的双层结构。与粗晶合金相比,纳米晶表面的钝化膜内及钝化膜/金属界面处Cr含量更高,即纳米化有利于Cr在界面及钝化膜内的富集。利用第一性原理进行理论计算,搭建Fe/FeO界面、Fe12O18晶胞分别模拟界面及钝化膜内的理论模型,结果揭示钝化膜/金属界面处是Cr元素稳定存在的位置,而且钝化膜随着Cr含量的增加而更加稳定。结合点缺陷理论(PDM模型)分析,揭示纳米化通过加速Fe的溶解及其空位的扩散,尤其是在界面层,促进了Cr元素的富集。研究结果表明,Cr含量不高于30%的Fe-Cr合金(Fe-lOCr, Fe-20Cr. Fe-30Cr)在HCl+NaCl (pH=2, [Cr-]= 0.1M)溶液中浸泡5min后,金属表面Cl-的吸附量随着Cr含量的增加而增加；当Cr含量在50%和75%时,金属表面更容易形成Cr的氧化物为主的钝化膜,从而阻止了Cl-的吸附。利用第一性原理计算的方法构建Cl-/Fe界面模型,找到Cl-吸附于金属表面的最稳定位置,用Cr来取代界面处的Fe,然后对Cl-在材料表面吸附后的Cl-吸附能和理论吸附距离进行理论计算,结果表明Cl-吸附能和吸附距离都随着合金中Cr在界面处含量的增加而降低。另外,从电子角度分析,金属价电子的结构与Cl-的吸附紧密相关,由于Cr元素拥有更多的3d空轨道,所以其与Cl-杂化能力更强,易于Cl-的吸附,理论计算结果也与UPS测试结果相吻合。从而解释了Cl-的吸附量随着Cr含量的增加而增加的实验现象。进一步对Cl-在钝化膜内的传输行为进行研究。结果表明在HCl+NaCl(pH=2,[Cr-] =0.1M)酸性溶液中,纳米晶薄膜抑制了O和Cl-的吸附,加速了钝化膜的形成,纳米化有利于Cr元素在钝化膜内层的富集。第一性原理计算表明氧空位在Fe/FeO界面处最稳定,纳米晶有利于在界面处产生空位。由于Cr在钝化膜内富集,Cl-从钝化膜进入到金属/钝化膜界面的扩散过程变得困难,纳米晶不利于Cl-的进入和传输。第一性原理计算和UPS实验分别从热力学和电子角度对纳米化促使Fe-20Cr合金钝化,提高合金抗腐蚀能力的实验结果给出了理论解释。
[Abstract]:Magnetron sputtering stainless steel nanocrystalline films have better corrosion resistance than coarse-grained materials of the same composition. It was found that the surface nanocrystalline of Cr could promote the enrichment of Cr in the passivation film and inhibit the surface adsorption of Cl-, but the microcosmic and essential mechanism of the nanocrystalline reaction was not clear. In this thesis, Fe-Cr alloy, a model alloy system of stainless steel, was used to passivate the sputtering nanocrystalline thin films by traditional electrochemical measurement, surface analysis and first-principle calculation. The surface adsorption and transport behavior of Cl- in the passivation film were studied. The effect of nanocrystalline on the corrosion behavior of Fe-Cr alloy is discussed. The results of ARXPS surface analysis show that, The passivation films formed on the surface of coarse-grained Fe-20Cr alloys and nano-crystalline films deposited in 0.15 MB (OH) _ 3 0.075M Na2B4O7 10H2O (pH8.6) buffer solution have hydrated layers with outer hydroxides and oxygen as inner layers. The double layer structure of the chemical layer. Compared with coarse-grained alloy, the Cr content in the passivation film and the passivation film / metal interface on the nanocrystalline surface is higher than that in the coarse crystal alloy, that is, the nanocrystalline content is favorable to the enrichment of Cr in the interface and the passivation film. The theoretical calculation was carried out by the first principle, and the Fe/FeO interface was set up, and the theoretical models of the interface and the passivation film were simulated by Fe12O18 unit cell, respectively. The results showed that the passive film / metal interface was the stable position of the Cr element. And the passivation film is more stable with the increase of Cr content. The analysis of PDM model revealed that nanocrystalline promoted the enrichment of Cr elements by accelerating the dissolution of Fe and the diffusion of vacancies, especially in the interfacial layer. The results show that the content of Cr in Fe-Cr alloy (Fe-lOCr, Fe-20Cr.) is less than 30%. Fe-30Cr) after soaking 5min in HCl NaCl (pH=2, [Cr-] = 0.1M solution, the amount of Cl- adsorbed on the metal surface increased with the increase of Cr content. When the content of Cr is 50% and 75%, it is easier for the metal surface to form a passivation film dominated by the oxide of Cr, thus preventing the adsorption of Cl-. The interface model of Cl-/Fe was constructed by first-principle calculation method, and the most stable position of Cl- adsorbed on metal surface was found. Cr was used to replace the Fe, at the interface. Then the adsorption energy of Cl- and the adsorption distance of Cl- on the surface of Cl- were calculated theoretically. The results show that the adsorption energy and distance of Cl- decrease with the increase of the content of Cr at the interface of the alloy. In addition, from the electronic point of view, the structure of metal valence electrons is closely related to the adsorption of Cl-. Because the element of Cr has more 3D empty orbitals, it has stronger hybrid ability with Cl- and is easy to adsorb Cl-. The theoretical results are in good agreement with the UPS test results. The experimental phenomenon that the adsorption amount of Cl- increases with the increase of Cr content is explained. The transport behavior of Cl- in the passivation film was studied. The results show that in the acidic solution of HCl NaCl (pH=2, [Cr-] = 0.1M, nanocrystalline film inhibits the adsorption of O and Cl-, and accelerates the formation of passivation film. The nanocrystalline concentration of Cr element in the inner layer of passivation film is favorable. First-principle calculations show that oxygen vacancies are most stable at the Fe/FeO interface, and nanocrystals are conducive to the generation of vacancies at the interface. Because of the enrichment of Cr in the passivation film, the diffusion process of Cl- from the passivation film to the interface of the metal / passivation film becomes difficult, and the nanocrystalline is not conducive to the entry and transport of Cl-. The thermodynamic and electronic results of the first principle calculation and UPS experiments were used to explain the experimental results of the nanocrystalline passivation and corrosion resistance of Fe-20Cr alloys.
【学位授予单位】：大连理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG174.4

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