氘、氦及其混合物状态方程第一原理研究

利用量子分子动力学方法对氘、氦及其混合物的状态方程进行了研究. 计算了氦在密度0.32-5 g/cm³, 温度1000-50000 K范围内的状态方程, 并与化学模型的结果进行了比较; 同时计算了冲击Hugoniot曲线, 与气炮实验的结果符合得很好. 通过计算对分布函数及态密度, 探讨了氦在高温高压下发生金属-绝缘体转变的机理. 计算了氘在密度0.19-0.84 g/cm³, 温度20-50000 K范围内的状态方程; 并计算了理论Hugoniot状态, 由于没有考虑原子的零点运动, 在低温区, 理论结果比实验值小. 对氘氦混合物的状态方程进行了研究, 计算了温度和密度区间为100-50000 K, 0.19-0.84 g/cm³, 不同混合度下的293个状态点的状态方程. 对线性混合近似进行了考查, 结果表明线性混合近似是一个粗略的近似.     

碳化硅中惰性气体离子辐照引起缺陷的研究

综述了有关碳化硅材料中惰性气体离子引起辐照缺陷研究的进展。包括借助多种方法对氦离子辐照的碳化硅中氦泡集团形成的剂量阈值的实验研究,基于过冷固体假设对氦泡阈值的理论解释,不同剂量氦泡的两种形态及其机理的研究,以及重惰性气体离子（Ne,Xe）辐照下缺陷演化的特点。This paper gives a review of our recent studies on the defect production in silicon carbide induced by energetic inert-gas-ion irradiation. The work includes the study of the dose threshold for helium bubble formation by combining TEM, RBS-channeling and PAS, the theoretical analysis of the dose threshold for bubble formation based on the Frozen-Matrix assumption, two types of bubble arrangement at different dose regions and the study of damage um-ion production behavior in the case of irradiation with heavier inert-gas-ions （ Ne, Xe） as a comparison to heliirradiation.     

氦泡对铝的弹性性质的影响

主要利用分子动力学方法模拟计算了含氦泡的铝的弹性性质,首先,应用第一性原理的方法计算了Al-He的相互作用势.其次,从两个不同的方面研究了氦泡对铝弹性常数的影响,一是不同的氦泡尺寸(直径分别是16, 20, 25, 30和3.5nm),二是不同的氦泡压力(即固定氦泡大小,氦泡内氦原子的个数与空位的比分别大约是5％,15％,45％ 和85％).结果表明弹性常数随着氦泡半径的增大而减小,对于固定大小的氦泡,随着氦泡内的压力变化弹性常数基本保持恒定.最后通过建立弹性复合体模型,得到的解析解定性上解释了氦泡的大小以及内压对铝的弹性常数的影响,与分子动力学模拟结果吻合. 关键词： 辐照损伤 氦泡 分子动力学 弹性常数     

电子束辐照下的注氘铝的结构变化

利用离子加速器在室温下对纯铝注入氘离子或氢离子,然后在透射电镜中对注氘铝或注氢铝中的气泡进行电子束辐照,发现在电子束辐照下气泡会长大、破裂.随着气泡的变化,选区电子衍射花样中出现了表示多晶存在的衍射环.这表明电子束辐照气泡时,发生某种放热现象,从而使附近的铝先熔化后再凝固,由单晶变为多晶.     

氘氘冰层贯穿性缺陷对ICF冷冻靶内爆性能的影响

使用二维多群辐射扩散流体力学程序LARED-S, 模拟研究DD冰贯穿性缺陷在方波驱动DD冷冻靶内爆过程中的演化行为及其对内爆性能的影响。模拟结果表明: DD冰层贯穿性缺陷显著降低DD冷冻靶内爆的中子产额, 二维模拟产额仅为一维结果的23.8%。DD冰层贯穿性缺陷使靶丸CH(Si)的烧蚀层生成大幅度的尖钉, 穿透到芯部热斑区。在中子bang-time时刻, 热斑区混入了487 ng的烧蚀物质, 使芯部韧致辐射漏失功率相对一维理想内爆显著升高, 离子温度与DD核反应速度相应降低。同时, 高密度的烧蚀层尖钉把DD热斑推离球心, 显示明显的P1不对称性, 而且高温热斑具有定向流动速度, 降低了内爆动能转化为热斑内能的效率。     

中子辐照铝的微观结构变化

研究了中子辐照后铝的微观结构和力学性能的变化。发现中子辐照使铝的硬度有了一定的提高,同时在铝的内部产生了大量细小的位错环。The change of microstructure and mechanical property in neutron irradiated aluminum was studied. It is found that neutron irradiation increased the hardness of the aluminum and caused the formation of many small dislocation loops in the aluminum.     

金属钨中氦行为的分子动力学模拟

采用分子动力学方法模拟了氦在金属钨中的扩散聚集行为. 首先,建立了氦与钨原子间相互作用势,短程部分采用ZBL势形式,长程部分采用从头算法数据,实现了两者之间的平滑连接. 通过计算氦在钨中不同间隙位的形成能发现,单个氦原子更易存在于金属钨中的四面体间隙位,这与最新的研究成果是一致的. 在400-1200 K的温度范围内,考察了氦原子在金属钨中的扩散行为,获得了扩散迁移能,其值介于实验值和从头算法结果之间. 最后,研究了氦的聚集行为,从能量的角度考察了氦团簇形成初期的生长机理. 研究发现,在氦团簇形成初期,氦团簇对氦的结合能随着氦团簇的生长有逐渐增大的趋势,说明氦团簇吸收氦的能力逐渐增强. 关键词： 氦扩散 氦团簇 辐照损伤 分子动力学模拟     

氦离子低温预辐照对不锈钢中氦泡生长抑制作用的Monte Carlo模拟研究

实验中已发现氦离子低温预辐照不锈钢材料能有效抑制高温辐照阶段的氦泡生长,但这一结果一直缺少理论解释.基于持续注入粒子的三维格子气模型,采用Monte Carlo模拟方法研究了不同温度模式对氦泡生长行为的影响.研究发现,计算结果能很好地再现氦离子低温预注入抑制高温氦泡生长的实验现象,其原理为低温预注入时材料中形成了较高数密度的小氦泡,由于氦泡数量较多从而限制了氦泡平均尺寸的增大.     

级联弧放电氦等离子体特性研究

采用另加偏压的单阴极弧氦放电直线等离子体装置对氦等离子体的基本特性进行了研究。对氦轴向输运规律做了描述并与光谱测量数据做了定性地比较。实验结果表明,氦等离子体的电子温度与电子密度均随放电电流、约束磁场的增加而增加。氦原子与氦离子的辐射光谱随放电电流、偏压、磁场的变化规律进行了测量分析,同时氦离子对钨靶积分辐照效应进行了观察。这些结果不但提供了氦等离子体的基本特性,对于研究氦离子与面向等离子材料相互作用导致产生气泡、肿胀、脆化损伤等的评估,特别是对将来伴有(n, α)反应时具有一定的参考价值。     

表面效应对铁<100>间隙型位错环的影响

在材料辐照损伤过程中,间隙型位错环的形成及动力学行为严重影响材料在辐照条件下的服役行为.在常用的以体心立方铁为基的合金材料中,1/2<111>和<100>是两种主要的位错环,其对辐照损伤的影响一直都是核材料领域研究的热点之一.在之前的研究中,人们对{111}面与单个1/2<111>位错环的相互作用进行了深入研究,发现表面对位错环性质确实有重要的影响.采用分子动力学方法,在原子尺度详细研究了另一个重要的表面铁{100}面对<100>间隙型位错环动力学过程的影响.模拟发现位错环伯格斯矢量与表面法线方向的关系、距表面的深度、位错环之间的相互作用以及温度等,都对位错环与表面的相互作用产生重要影响,其中,表面作用下的伯格斯矢量的演化以及<100>位错环在此过程中的一维运动首次被发现.基于这些模拟结果,就<100>位错环对表面辐照损伤结构的影响进行详细地研究,给出<100>位错环对表面凹凸结构的贡献,这些结果为理解辐照过程中材料表面的演化提供一种可能的解释.     

Microstructure change in deuterium implanted CLAM steel induced by electron irradiation

As Reduced Activation Ferritic/Martensitic (RAFM) steel is considered the primary candidate for use as a structural material in fusion power reactors,many countries are developing different kinds of RAFM.China is developing new CLAM (China Low Activation Martensitic) steel.The study investigates microstructural changes in CLAM steel implanted with deuterium ions induced by 1250 keV electron irradiation from R.T.to 873 K,and observes both the growth and shrinkage of the defect clusters produced by deuterium ...     

Irradiation effect of yttria-stabilized zirconia by high dose dual ion beam irradiation

Yttria-stabilized zirconia （YSZ） is irradiated with 2.0-MeV Au2＋ ions and 30-keV He＋ ions. Three types of He, Au, Au ＋ He （successively） ion irradiation are performed. The maximum damage level of a sequential dual ion beam implanted sample is smaller than single Au ion implanted sample. A comparable volume swelling is found in a sequential dual ion beam irradiated sample and it is also found in a single Au ion implanted sample. Both effects can be explained by the partial reorganization of the dislocation network into weakly damaged regions in the dual ion beam implanted YSZ. A vacancy-assisted helium trapping/diffusion mechanism in the dual ion beam irradiated condition is discussed. No phase transformation or amorphization behavior happens in all types of ion irradiated YSZ.     

质子辐照对纯铝薄膜微观结构的影响

利用透射电子显微镜(TEM)详细分析了不同剂量的质子辐照纯铝薄膜样品的微观结构, 质子的能量E=160 keV.实验表明,质子辐照能够在Al薄膜中诱发空位位错圈,在实验范围内,位错密度随辐照剂量的增加而增加;质子辐照在1×10¹¹—4×10¹¹/mm²范围内随辐照剂量的增加,位错圈数量密度以及位错圈尺寸都随之增加.在较高剂量6×10¹¹/mm²辐照下,位错圈数量密度减小,但其尺寸显著 关键词： 质子辐照 空位簇缺陷 位错圈 微观结构     

Effect of simultaneous helium implantation on the microstructure evolution of Inconel X-750 superalloy during dual-beam irradiation

This study focuses on investigation into the effect of helium implantation on microstructure evolution in Inconel X-750 superalloy during dual-beam (Ni⁺/He⁺) irradiation. The 1 MeV Ni⁺ ions with the damage rate of 10^?3 dpa/s as well as 15 keV He⁺ ions using rate of 200 appm/dpa were simultaneously employed to irradiate specimens at 400 °C to different doses. Microstructure characterization has been conducted using high-resolution analytical transmission electron microscopy (TEM). The TEM results show that simultaneous helium injection has significant influence on irradiation-induced microstructural changes. The disordering of γ′ (Ni₃ (Al, Ti)) precipitates shows noticeable delay in dose level compared to mono heavy ion irradiation, which is attributed to the effect of helium on promoting the dynamic reordering process. In contrast to previous studies on single-beam ion irradiation, in which no cavities were reported even at high doses, very small (2–5 nm) cavities were detected after irradiation to 5 dpa, which proved that helium plays crucial role in cavity formation. TEM characterization also indicates that the helium implantation affects the development of dislocation loops during irradiation. Large 1/3 〈1?1?1〉 Frank loops in the size of 10–20 nm developed during irradiation at 400 °C, whereas similar big loops detected at higher irradiation temperature (500 °C) during sole ion irradiation. This implies that the effect of helium on trapping the vacancies can help to develop the interstitial Frank loops at lower irradiation temperatures.     

Dynamical response of helium bubble motion to irradiation with high-energy self-ions in aluminum at high temperature

Brownian-type motion of helium bubbles in aluminum and its dynamical response to irradiation with 100-keV Al⁺ ions at high temperatures has been studied using in situ irradiation and transmission electron microscopy. It is found that, for most bubbles, the Brownian-type motion is retarded under irradiation, while the mobility returns when the irradiation is stopped. In contrast, under irradiation, a small number of bubbles display exceptionally rapid motion associated with the change in bubble size. These effects are discussed in terms of the dynamical interaction of helium bubbles with cascade damage formed by the high-energy self-ion irradiation.     

In-situ TEM observation of the evolution of helium bubbles in Mo during He+ irradiation and post-irradiation annealing

The evolution of helium bubbles in purity Mo was investigated by in-situ transmission electron microscopy (TEM) during 30 keV He⁺ irradiation (at 673 K and 1173 K) and post-irradiation annealing (after 30 keV He⁺ irradiation with the fluence of 5.74×10¹⁶ He⁺/cm² at 673 K). Both He⁺ irradiation and subsequently annealing induced the initiation, aggregation, and growth of helium bubbles. Temperature had a significant effect on the initiation and evolution of helium bubbles. The higher the irradiation temperature was, the larger the bubble size at the same irradiation fluence would be. At 1173 K irradiation, helium bubbles nucleated and grew preferentially at grain boundaries and showed super large size, which would induce the formation of microcracks. At the same time, the geometry of helium bubbles changed from sphericity to polyhedron. The polyhedral bubbles preferred to grow in the shape bounded by {100} planes. After statistical analysis of the characteristic parameters of helium bubbles, the functions between the average size, number density of helium bubbles, swelling rate and irradiation damage were obtained. Meanwhile, an empirical formula for calculating the size of helium bubbles during the annealing was also provided.     

Inelastic electron irradiation damage in hexagonal boron nitride

We present a study of the inelastic effects caused by electron irradiation in monolayer hexagonal boron nitride (h-BN). The data was obtained through in situ experiments performed inside a low-voltage aberration-corrected transmission electron microscope (TEM). By using various specialized sample holders, we study defect formation and evolution with sub-nanometer resolution over a wide range of temperatures, between −196 and 1200 °C, highlighting significant differences in the geometry of the structures that form. The data is then quantified, allowing insight into the defect formation mechanism, which is discussed in comparison with the potential candidate damage processes. We show that the defect shapes are determined by an interplay between electron damage, which we assign to charging, and thermal effects. We additionally show that this damage can be avoided altogether by overlapping the samples with a monolayer of graphene, confirming this for h-BN and providing a way to overcome the well-known fragility of h-BN under the electron beam.     

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.