注氢铁基二元合金中辐照位错环演化及退火温度影响研究

本文基于注氢纯铁和铁基二元合金(Fe-3%Cr、Fe-1.4%Ni和Fe-1.4%Mn,质量分数)开展常规透射电镜(200 kV)的原位表征观察,揭示了材料中辐照位错环的形态、尺寸演化行为及退火温度影响,并依据辐照损伤演化理论、退火过程中位错环平均尺寸变化推断得到空位型位错环形成温度的范围.注氢纯铁中空位型位错环的形成温度(T_c)约为500℃;添加Ni可使T_c降低至～450℃,添加Cr可使T_c升高至600℃以上,而Mn的作用与Cr相似,亦可使T_c升高.注氘实验和热脱附谱分析进一步表明,纯铁和铁基二元合金中空位型位错环的形成温度受氢同位素与空位结合、释放过程影响.合金元素Ni对氢同位素与空位的结合、释放有促进作用,故导致T_c降低;而Cr和Mn均对氢同位素与空位的结合、释放产生抑制作用,故导致T_c升高.本文展示的有关合金元素对空位型位错环形成温度影响的研究将有助于更深刻理解铁基合金体系中损伤结构演化和辐照肿胀产生机理.     

氢离子辐照纯钒中形成的位错环

钒合金作为聚变堆候选材料, 其辐照损伤行为一直是关注的重点. 研究辐照时形成的位错环的性质, 其意义在于揭示纯钒中辐照空洞的长大机理. 这种机理表现为不同类型位错环对点缺陷吸收的偏压不同, 从而影响金属的辐照肿胀. 本文利用加速器对纯钒薄膜样品进行氢离子辐照, 然后, 利用透射电镜的inside-outside方法分析氢离子辐照所形成的位错环的类型. 结果表明, 在氢离子辐照纯钒中没有发现柏氏矢量b=<110>的位错环, 只有柏氏矢量b=1/2<111>和b=<110>的位错环, 这两种位错环的惯性面处于{110}-{112}之间. 能确定性质的位错环全部为间隙型位错环, 未发现空位型位错环.     

聚变材料钨辐照后退火形成的位错环特性及inside-outside衬度分析

对纯钨透射电镜薄膜样品在400℃进行了58 keV、1×10¹⁷ cm^-2(约0.1 dpa)的氘离子辐照,辐照后进行了900℃/1 h的退火处理.离子辐照产生了平均尺寸为(11.10±5.41)nm,体密度约为2.40×10²² m^-3的细小位错环组织,未观察到明显的空洞组织.辐照后退火造成了位错环尺寸的长大和体密度的下降,分别为(18.25±16.92) nm和1.19×10²² m^-3.通过透射电镜的衍射衬度分析,判断辐照后退火样品中的位错环主要为a/2<111>类型位错环.通过“一步法” inside-outside衬度分析判断位错环为间隙型位错环.辐照后退火还造成了较大位错环之间接触融合,形成不规则形状的大型位错环.此外,退火后样品中还观察到了尺寸为1—2 nm的细小空洞组织.     

注氢纯铝中间隙型位错环一维迁移现象的原位观察

核聚变堆材料在高能粒子辐照过程中会产生大量点缺陷,导致辐照脆性和辐照肿胀等现象.因而,研究点缺陷在辐照过程中的演变过程至关重要.点缺陷团簇的一维迁移现象是这种演变过程的主要研究内容之一.本文采用普通低压(200 kV)透射电镜,在室温条件下对注氢纯铝中的间隙型位错环在电子辐照下的一维迁移现象进行了观察和分析.在200 keV电子辐照下,注氢纯铝中的位错环可多个、同时发生一维迁移运动,也可单个、独立进行一维迁移运动.位错环沿柏氏矢量1/3<111>的方向可进行微米尺度的一维长程迁移,沿柏氏矢量1/2<110>的方向一维迁移也可达数百纳米.电子束辐照时产生的间隙原子浓度梯度是引起位错环一维迁移并决定其迁移方向的原因.位错环发生快速一维迁移时,其后会留下一条运动轨迹;位错环一维迁移的速率越快,运动的轨迹则越长,在完成迁移过后的几十秒内这些运动轨迹会逐渐消失.     

bcc Fe中刃型位错的结构及能量学研究

基于位错理论，利用分子动力学方法建立了〈100〉{010}，〈100〉{011}，1/2〈111〉{011}和1/2〈111〉{112}刃型位错的芯结构，并计算了这四种刃型位错的形成能、位错芯能量和芯半径.计算结果表明：〈100〉{010}和〈100〉{011}刃型位错的形成能比1/2〈111〉{011}和1/2〈111〉{112}刃型位错的要高，这表明〈100〉刃型位错比1/2〈111〉刃型位错更难形成.而〈100〉{010}和〈100〉{011}刃型位错的芯半径比1/2〈111〉{011}和1/2〈111〉{112}刃型位错的小，这说明在1/2〈111〉刃型位错中位于奇异区的原子数多于〈100〉刃型位错，而这些原子要比完整晶体中的原子具有更大的活性.可见，1/2〈111〉刃型位错比〈100〉刃型位错更易运动，且〈100〉刃型位错在bcc Fe中难以形成. 关键词： bcc Fe 刃型位错 分子动力学模拟     

Fe中刃型位错上扭折及掺杂体系的电子结构

利用离散变分方法和DMol方法,研究了体心立方Fe中1/2［111］（110）刃型位错上扭折及掺杂（N,O）体系的电子结构.能量（杂质偏聚能及格位能）计算结果表明,杂质元素N,O进入扭折芯区的偏聚趋势,这与位错扭折引起的晶格畸变有关.同时,在杂质元素周围有一些电荷聚集,导致扭折上电荷的不均匀分布,杂质原子得到电子,其周围Fe原子失去电子.由于N原子的2p轨道与近邻Fe原子的3d4s4p轨道之间杂化,使N原子与近邻Fe原子间有较强的相互作用,不利于扭折的迁移,使位错运动受阻,有利于材料强度的提高;而O与最近邻Fe原子之间的相互作用较弱.杂质-扭折复合体的局域效应明显影响体系的电子结构、能量及性能. 关键词： 电子结构 刃型位错 扭折 杂质元素     

线刃型位错高斯光束在生物组织中偏振态的变化

基于广义惠更斯-菲涅尔原理,推导了生物组织传输中线刃型位错高斯谢尔模型光束交叉谱密度矩阵元的解析表达式,并比较了不同束腰宽度ω_0x、离轴距离d、刃型位错斜率p、空间相关长度σ_yy、σ_xy对光束轴上偏振度P(0,0,L)、方位角θ(0,0,L)和椭圆率ε(0,0,L)的影响。研究表明,线刃型位错高斯谢尔模型光束ω_0x越大,d越大,p越小,P(0,0,L)和ε(0,0,L)变化越大且极值越小。σ_xy越大,P(0,0,L)、ε(0,0,L)和θ(0,0,L)的绝对值越大。当σ_yy>σ_xx时,源处θ<0,反之θ>0。σ_yy与σ_xx差值绝对值越小,P(0,0,L)、θ(0,0,L)和ε(0,0,L)的极值越大。随传输距离增大,P(0,0,L)、θ(0,0,L)和ε(0,0,L)最终趋于稳定。     

金刚石中氦、氢含量的变化及在金刚石生长中的意义

天然金刚石自中心至边缘的显微傅里叶变换红外光谱研究表明:氮和氢在金刚石中的分布是不均匀的,这说明金刚石在整个生长过程中的物质环境是有差异的;中心至边缘的含氮总量、C-H键含量的总体降低趋势表明金刚石的生长过程是一个氮、氢的消耗过程,而中部的升高变化说明金刚石生长环境中存在氮、氢的补充,但氮补充得比氢更早一些.据此,可以将金刚石的生长过程划分为早期成核与长大、中期长大及末期长大三个阶段,其中早期和末期是氮和氢的消耗阶段,中期需要进行氮和氢的补充,且氮应该更早补充.氢对金刚石的生长是有利的,氢和氮不是以氮氢化合物的形式存在于金刚石生长的物质环境中,这暗示着在高温高压合成金刚石中欲引入氢,应当避免氮氢化合物的形成.     

氢化非晶硅薄膜中氢含量及键合模式的红外分析

Fourier红外透射(FTIR)谱技术是研究氢化非晶硅（a-Si∶H）薄膜中氢的含量（CH）及硅—氢键合模式（Si-Hn）最有效的手段.对用等离子体化学气相沉积（PCVD）方法在不同的衬底温度（Ts）下制备出的氢化非晶硅薄膜，通过红外透射光谱的基线拟合、高斯拟合分析，得到了薄膜中的氢含量，硅氢键合模式及其组分，并分析了这些参量随衬底温度变化的规律.     

纳米晶硅薄膜中氢含量及键合模式的红外分析

采用传统射频等离子体化学气相沉积技术在100—350℃的衬底温度下高速沉积氢化硅薄膜. 傅里叶变换红外光谱和Raman谱的研究表明,纳米晶硅薄膜中的氢含量和硅氢键合模式与薄膜的晶化特性有密切关系,当薄膜从非晶相向晶相转变时,氢的含量减少了一半以上,硅氢键合模式以SiH₂为主. 随着衬底温度的升高和晶化率的增加,纳米晶硅薄膜中氢的含量以及其结构因子逐渐减少. 关键词： 氢化纳米晶硅薄膜 红外透射谱 氢含量 硅氢键合模式     

Evolution of dislocation loops in austenitic stainless steels implanted with high concentration of hydrogen

Abstract

It has been found that under certain conditions, hydrogen retention would be strongly enhanced in irradiated austenitic stainless steels. To investigate the effect of the retained hydrogen on the defect microstructure, AL-6XN stainless steel specimens were irradiated with low energy (100 keV) H₂⁺ so that high concentration of hydrogen was injected into the specimens while considerable displacement damage dose (up to 7 dpa) was also achieved. Irradiation induced dislocation loops and voids were characterised by transmission electron microscopy. For specimens irradiated to 7 dpa at 290 °C, dislocation loops with high number density were found and the void swelling was observed. At 380 °C, most of dislocation loops were unfaulted and tangled at 7 dpa, and the void swellings were observed at 5 dpa and above. Combining the data from low dose in previous work to high dose, four stages of dislocation loops evolution with hydrogen retention were suggested. Finally, molecular dynamics simulation was made to elucidate the division of large dislocation loops under irradiation.     

圆环电流的磁场以及两共轴圆环电流之间的相互作用力

直接由毕奥－萨伐尔定律计算圆环电流在空间任一点产生的磁场，并由此求出两共轴圆环电流之间的相互作用力。     

Formation and growth of dislocation loops in ZnTe under irradiation of low energy Ar+-Ions

Abstract

Defects produced in ZnTe single crystals by Ar⁺ bombardment during ion milling for transmission electron microscopy studies are investigated in detail. The defects have been identified to be interstitial type Frank loops. Influences of ion energy and specimen temperature during the irradiation on the defect geometry are investigated. A model is proposed to describe the growing up of the loops.     

Characterization of the “native” surface thin film on pure polycrystalline iron: A high resolution XPS and TEM study

The characterization of the “native” surface thin film on pure polycrystalline iron has been studied by high resolution X-ray photoelectron (XP) spectroscopy of Fe 2p and O 1s regions. The film was allowed to form by exposing the sample to atmosphere at ambient conditions for a period of 1 h. The systematic approach used here includes the determination of curve fitting parameters from external standards and their use in fitting the raw data for the surface thin film. The quantitative high resolution XPS analysis involved an angle resolved study of the surface to determine the chemical composition and thickness of this native film. The film was found to be a mixture of Fe₃O₄ and Fe(OH)₂ with a thickness of 1.2 ± 0.3 nm. This conclusion is consistent with thermodynamics as indicated by the Pourbaix diagram for the Fe-H₂O system and the phase diagram for the Fe-oxygen system. A detailed TEM study of the native surface film also supports this conclusion.     

Displacement field induced by a vacancy in nickel and some implications for the solubility of hydrogen

The displacement field induced by a vacancy in nickel and its possible implications for the hydrogen solubility in the interstitial sites is investigated up to 1100 K. The displacement field is extracted from our previous atomistic-scale density functional theory calculations and is compared with continuous isotropic models with and without image forces due to the distribution of the defects. This procedure put in forward the contribution of the elastic anisotropy and the vacancy concentration on the elastic displacement field. Then, we calculate the dilatation of the interstitial sites due to the presence of the defect and the local hydrostatic stress acting on them. This local hydrostatic stress modifies the hydrogen solubility in the interstitial sites. Elastic distortions contribute to reduce the local solubility inside the vacancy core and the opposite out of it. Finally, we extract the elastic contribution of the trapping energy of hydrogen in the displacement field of the vacancy. We find that the elastic energy is significant only for the closest interstitial sites of the defect core and limits the attractive electronic contribution to the trapping energy. In addition, we show that the elastic anisotropy and the vacancy concentration have moderate effects on the local solubility in the displacement field close to the defect core.     

The interpretation of X-ray diffraction from the pyrocarbon in carbon/carbon composites with comparison of TEM observations

Three different carbon/carbon (C/C) composites based on needle-punched felt made of layered T700 carbon fiber cloth were fabricated by chemical vapor infiltration and were studied using transmission electron microscopy (TEM) and X-ray diffraction (XRD). The TEM observations show that one of the composites contains only low-textured pyrocarbon. The other two contain both low-textured and high-textured pyrocarbon, one with predominantly low-textured and the other with mainly high-textured pyrocarbon. High-resolution TEM images show that the high-textured pyrocarbon in the two composites has the same microstructure as local areas with the graphite structure. XRD measurements show that the interlayer spacing and crystallite size of pyrocarbon are not only affected by the poorly graphitized carbon fiber phase, but also by the amounts of the different types of pyrocarbon and the orientation of crystallites. Comparison of the TEM observations and the XRD measurements reveals that structural parameters, such as the interlayer spacing and crystallite size, of pyrocarbon in C/C composites as determined by XRD are not accurate. Therefore, XRD profiles of C/C composites should be interpreted with caution. TEM observations for detailed microstructure analysis of C/C composites are thus important.     

Study of defect evolution by TEM with in situ ion irradiation and coordinated modeling

The paper describes a novel transmission electron microscopy (TEM) experiment with in situ ion irradiation designed to improve and validate a computer model. TEM thin foils of molybdenum were irradiated in situ by 1?MeV Kr ions up to ～0.045 displacements per atom (dpa) at 80°C at three dose rates ?5?×?10^?6, 5?×?10^?5, and 5?×?10^?4?dpa/s – at the Argonne IVEM-Tandem Facility. The low-dose experiments produced visible defect structure in dislocation loops, allowing accurate, quantitative measurements of defect number density and size distribution. Weak beam dark-field plane-view images were used to obtain defect density and size distribution as functions of foil thickness, dose, and dose rate. Diffraction contrast electron tomography was performed to image defect clusters through the foil thickness and measure their depth distribution. A spatially dependent cluster dynamic model was developed explicitly to model the damage by 1?MeV Kr ion irradiation in an Mo thin foil with temporal and spatial dependence of defect distribution. The set of quantitative data of visible defects was used to improve and validate the computer model. It was shown that the thin foil thickness is an important variable in determining the defect distribution. This additional spatial dimension allowed direct comparison between the model and experiments of defect structures. The defect loss to the surfaces in an irradiated thin foil was modeled successfully. TEM with in situ ion irradiation of Mo thin foils was also explicitly designed to compare with neutron irradiation data of the identical material that will be used to validate the model developed for thin foils.     

The formation and migration of the vacancies in HCP metal Mg

The formation and migration energies of the mono- and di-vacancy in Mg crystal have been calculated using the modified analytical embedded atom method. The results show that, for mono-vacancy, the migration in the basal plane is slightly preferred to the migration out of the basal plane. For di-vacancy, the 1NN and 2NN configurations are not only easier to form but also more stable than the other configurations. The preferred migration mechanisms of the 1NN and 2NN di-vacancy are either invariable 1NN or 2NN configurations during migration in the basal plane or exchange 1NN for 2NN or 2NN for 1NN for migration out of the basal plane. These two-jump migration mechanisms of the di-vacancy, especially the former, are still preferred over the migration of the mono-vacancy. It is concluded that the greater the number of resting vicinity vacancies, the easier the migrating vacancy moves.     

On the formation of temperature-induced defects at the surface of TEM specimens prepared from TiAl using high-energy Gallium and low-energy Argon ions

ABSTRACT

Specimens for transmission electron microscopic (TEM) investigations were prepared from γ titanium aluminide alloys with Gallium and Argon ions using a focused ion beam (FIB) and a precision ion polishing system (PIPS). Preparation to electron transparency by Gallium ions alone leads to the formation of crystalline platelets of the α titanium phase at the specimen surfaces, revealed through conventional and high resolution (HR) TEM analysis. The platelets are assumed to precipitate from priorly formed amorphous layers. The required crystallisation temperature of about 480°C is generated through the ion bombardment implying that the γ titanium aluminides can be heated substantively during sputtering. The primary reason for this is the restricted transfer of heat away from the beam impact point when the specimen thickness comes close to the beam diameter. The formation of the platelets can be avoided by terminating the Gallium ion treatment prior to that, while providing for a sufficient thermal bonding of the specimen to the grid as well and polishing off the remaining material by Argon ions, which are much less focused and less energetic, so that the local heat peaks are reduced.