纯Fe表面机械研磨处理对Ti原子扩散特性影响的第一性原理计算及实验验证
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摘要
基于密度泛函理论的第一性原理方法,计算了空位对纯Fe晶格常数、局域态密度和热力学参数的影响规律,结合Ti原子在纯Fe中的过渡态搜索,阐明了空位对纯Fe表面Ti原子扩散特性的作用机制。模拟计算表明,引入空位后,体系晶格常数和局域态密度减小,Helmholtz自由能和结合能降低,声子振动内能、熵值和等容热容增加。bcc-Fe的3×3×3超胞含一个空位和两个空位时Ti原子的扩散势垒分别为0.659 eV和0.353 eV。不同温度下体系的扩散系数表明,纯Fe经表面机械研磨处理(SMAT)后,其在673 K即可达到未机械研磨时1 073 K的Ti原子扩散效果。在实验验证环节,借助扫描电镜(SEM)、能谱(EDS)仪和X射线衍射(XRD)仪观察及表征了Fe试样经SMAT处理和673 K双层辉光等离子渗Ti处理后的微观组织、截面元素分布及渗层物相结构。结果表明,增加空位浓度可以有效降低等离子渗钛温度,纯Fe表面生成了12μm左右的渗Ti层。本工作可为通过调控空位浓度实现低温渗钛的研究提供参考。
This contribution presents a first principles analysis and experimental study on how the mechanical attrition treatment of pure Fe surface influences Ti atoms diffusion. The influence of vacancies on lattice constant,local density of states,thermodynamic parameters of pure Fe was calculated by PAW method under the framework of density functional theory. Combined with transitional state search,the diffusion behavior of Ti atoms on the surface of pure Fe was investigated. The simulation and calculation showed that the increase of the vacancy concentration can lead to the decreases in lattice constant,local density of states,Helmholtz free energy and binding energy of the system,as well as the increments of phonon-assisted vibrational energy,entropy and constant volume heat capacity. For 3×3×3 supercells of Fe containing one vacancy and two vacancies,the energy barriers of Ti atom diffusion were calculated to be 0. 659 eV and 0. 353 eV,respectively. Moreover,it was found that the diffusion coefficient at 673 K on the mechanical attrition treated surface approaches the value at 1 073 K on the untreated surface. On the other hand,we conducted the experiments for the microstructure observation,cross-sectional elemental analysis and phase structure determination upon the Fe samples experienced SMAT and double glow plasma tetanizing at 673 K,by means of scanning electron microscopy( SEM),energy dispersive spectrometry( EDS) and X-ray diffraction( XRD). It was found that the SMAT-induced surface vacancies increment of pure Fe can effectively reduce diffusion temperature,and the formation of about 12 μm thin titanium infiltration layer on the sample surface was observed. Our work is expected to provide a reference for the study of low-temperature plasma titanizing by tailoring surface vacancy concentration.
This contribution presents a first principles analysis and experimental study on how the mechanical attrition treatment of pure Fe surface influences Ti atoms diffusion. The influence of vacancies on lattice constant,local density of states,thermodynamic parameters of pure Fe was calculated by PAW method under the framework of density functional theory. Combined with transitional state search,the diffusion behavior of Ti atoms on the surface of pure Fe was investigated. The simulation and calculation showed that the increase of the vacancy concentration can lead to the decreases in lattice constant,local density of states,Helmholtz free energy and binding energy of the system,as well as the increments of phonon-assisted vibrational energy,entropy and constant volume heat capacity. For 3×3×3 supercells of Fe containing one vacancy and two vacancies,the energy barriers of Ti atom diffusion were calculated to be 0. 659 eV and 0. 353 eV,respectively. Moreover,it was found that the diffusion coefficient at 673 K on the mechanical attrition treated surface approaches the value at 1 073 K on the untreated surface. On the other hand,we conducted the experiments for the microstructure observation,cross-sectional elemental analysis and phase structure determination upon the Fe samples experienced SMAT and double glow plasma tetanizing at 673 K,by means of scanning electron microscopy( SEM),energy dispersive spectrometry( EDS) and X-ray diffraction( XRD). It was found that the SMAT-induced surface vacancies increment of pure Fe can effectively reduce diffusion temperature,and the formation of about 12 μm thin titanium infiltration layer on the sample surface was observed. Our work is expected to provide a reference for the study of low-temperature plasma titanizing by tailoring surface vacancy concentration.
引文
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2 Tao N R. Surface Nanocrystallization microstructure and grain refinement mechanism of pure Fe and Inconel 600 caused by surface mechanical attrition treatment. Master’s Thesis, Institute of Metal Research, Chinese Academy of Science, China,2003(in Chinese).陶乃镕. 表面机械研磨导致的纯Fe和Inconel 600表面纳米化微观结构及晶粒细化机制研究. 硕士学位论文, 中国科学院金属研究所,2003.
3 Wang H, Zhan Z L, Wu Y X, et al. Transactions of Materials and Heat Treatment,2013,34(s2),184(in Chinese).王虎, 詹肇麟, 吴云霞, 等. 材料热处理学报,2013,34(s2),184.
4 Tao N R, Sui M L, Lu J, et al. Nanostructured Materials,1999,11(4), 433.
5 Tao N R, Wang Z B, Tong W P, et al. Acta Materialia,2002, 50(18),4603.
6 Tong W P, Tao N R, Wang Z B, et al. Science,2003,299(5607), 686.
7 Tong W P, Han Z, Wang L M, et al. Surface & Coatings Technology,2008,202(20),4957.
8 Zhang Y M, Li Z H, Xu Z. Journal of Taiyuan University Technology,2009,40(3),283(in Chinese).张艳梅, 李忠厚, 徐重. 太原理工大学学报,2009,40(3),283.
9 Liu H, Ke F J, Pan H, Zhou M. Acta Physca Sinica,2007,56(1),407(in Chinese).刘浩, 柯孚久, 潘晖, 等. 物理学报,2007,56(1),407.
10 An Y L. Investigation of relative problem about pire iron surface mechanical attrition treatment and first-principles calculations of carbon monoxide surcace absorption. Master’s thesis, Taiyuan University of Technology,China,2011(in Chinese).安艳丽. 纯铁表面机械研磨相关问题及表面吸附CO的第一性原理研究. 硕士学位论文,太原理工大学,2011.
11 Gao Y. Vacuum,1993(6),53(in Chinese).高原. 真空,1993(6),53.
12 Yu X, Zhan Z, Rong J, et al. Chemical Physics Letters,2014,600,43.
13 Yu X, Rong J, Zhan Z, et al. Materials & Design,2015,83,15.
14 Yu X, Zhan Z. Nanoscale Research Letters,2014,9(1),516.
15 Villars P, Cenzual K. Pearson's crystal data?:Crystal structure database for inorganic compounds, ASM International, Ohio,2007.
16 Li L H, Wang W L, Hu L, et al. Intermetallics,2014,46,21.
17 Liu N N, Song R B, Sun H Y, et al. Acta Physica Sinica, 2008,57(11),7150(in Chinese).刘娜娜, 宋仁伯, 孙翰英,等. 物理学报,2008,57(11),7150.
18 Martienssen W, Warlimont H. Springer handbook of condensed matter and materials data,Springer Science & Business Media, Berlin, 2006.
19 Zhao Y H, Lu K. Physical Review B,1997,56(22),14330.
20 Yang C C, Li S. Physical Review B,2007,75(16),165413.
21 Safaei A. The Journal of Physical Chemistry C,2010,114(32),13482.
22 Sun C Q, Wang Y, Tay B K, et al. The Journal of Physical Chemistry B,2002,106(41),10701.
23 Wert C, Zener C. Physical Review,1949,76(8),1169.
24 Yang B, Wang L G, Yi Y, et al. Acta Physica Sinica,2015,64(2),356(in Chinese).杨彪, 王丽阁, 易勇,等.物理学报,2015,64(2),356.
25 Laidler K J. Journal of Chemical Education,1984,61(6),494.