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     

Microplastic deformation of polycrystalline iron and molybdenum subjected to high-current electron-beam irradiation

A technique for determination of residual stresses at various distances from the irradiated surface is proposed. It is established for iron and molybdenum that compressive stresses are set up under irradiation by low-energy high-current electron beams and that their values decrease sharply with increasing distance from the surface. The residual stresses are much smaller in absolute magnitude than those operating during irradiation. It is shown that the change in resistance to microplastic deformation on irradiation with low-energy high-current electron beams is governed not only by formation of a gradient dislocation substructure in the surface layer, but also by the residual stresses and the appearance of the Bauschinger effect.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 126–132, March, 1996.     

Microstructure of high-pressure-synthesized diamonds under rapid quenching and electron irradiation

A type of synthetic diamond single crystal about 0.4–0.5 mm in dimension prepared under high pressure–high temperature (HPHT) in the presence of a FeNi molten catalyst was quenched from HPHT and irradiated with 300 keV electrons at room temperature. Transmission electron microscopy was employed to examine the microstructure of the diamond single crystal before and after electron irradiation. It was found that there exists a large amount of cellular interfaces in the quenched diamond sample, which indicates the growth condition of the diamond under HPHT. Hexagonal dislocation loops about several tens of nanometers in dimension were observed in the high-pressure-synthesized diamond single crystal before electron irradiation, which strongly suggests that a number of vacancies were quenched-in due to rapid quenching from high temperature at the end of diamond synthesis, and were aggregated in the synthetic diamond to form vacancy disks on the (111) plane, the collapse of such vacancy disks forming vacancy-type dislocation loops. After electron irradiation, it was found that defect clusters present as interstitial-character dislocation loops were formed in the electron-irradiated region of the diamond. The interstitial dislocation loops grow with increase of the irradiation time. The present study, in comparison to previous work on ion implantation on diamond, indicates that electron irradiation does not induce a phase transformation but produces interstitial dislocation loops due to the migration of interstitial atoms and vacancies. The result of the study directly indicates that interstitials and vacancies in diamond are mobile at room temperature under electron irradiation. Nitrogen, as the most important kind of impurity contained in the HPHT as-grown diamond, probably acts as nucleation of the interstitial loops. Received: 16 November 2001 / Accepted: 12 June 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. E-mail: yinlw@sdu.edu.cn     

铸态AZ31镁合金强流脉冲离子束改性

利用强流脉冲离子束（C+,H+）对变形镁合金AZ31的压铸件靶材分别进行1,5,10,20,30,50和100次辐照实验,分析辐照前后表面形貌和相组成,并检测辐照表面及横截面沿深度方向显微硬度。结果表明:HIPIB辐照次数对靶材形貌影响较大,多次辐照使靶材熔坑呈周期性变化趋势;-Mg17Al12相弥散分布于-Mg相中。1～30次辐照,表面显微硬度提高,其主要原因为晶粒细化及微应变导致的晶体缺陷;30～50次辐照,显微硬度显著降低,其原因在于晶体缺陷的演变,如位错移动导致的小角度晶界形成,甚至出现回复再结晶过程;50～100次辐照表面显微硬度略有降低,其原因在于辐照表面组织结构及热力学行为达到稳定态。辐照效应形成冲击应力波导致长程硬化,20次辐照的横截面显微硬度在距表层30 m和240 m处分别达到极大值1.0 GPa和1.3 GPa。     

In situ and tomographic observations of defect free channel formation in ion irradiated stainless steels

The effects of heavy-ion irradiation on dislocation processes in stainless steels were investigated using in situ irradiation and deformation in the transmission electron microscope as well as post mortem electron tomography to retrieve information on the three-dimensional dislocation state. Irradiation-induced defects were found to pose a strong collective barrier to dislocation motion, leading to dislocation pileups forming in grain interiors and at grain boundaries. The passage of multiple dislocations along the same slip plane removes the irradiation defects and leads to the eventual formation of a defect-free channel. These channels are composed of densely tangled dislocation networks which line the channel-matrix walls as well as residual dislocation debris in the channel interiors. The structures of the dislocation tangles were found to be similar to those encountered in later stages of deformation in unirradiated materials, with the exception that they developed earlier in the deformation process and were confined to the defect free channels. Also, defect free channels were found to widen through both source widening as well as complex cross-slip mechanisms.     

High-speed etching of hexagonal GaN by laser ablation and successive chemical treatment

Photostimulated direct etching of GaN has been demonstrated with extremely high etching rate up to 135 nm/pulse. The process consists of laser irradiation and ex-situhydrochloric acid treatment. Not only deep etching but also a highly planarized surface are obtained by an increase in laser fluence and the number of pulses. Seven-pulse irradiation at 1 J/cm² decreases surface average roughness (R_a) to ~2 nm from ~10 nm of the untreated sample. No deep-level emission (450-600 nm) is detected in photoluminescence measurement on the samples irradiated with laser fluences as high as 3 J/cm².     

Formation of defect structure by the effect of a gas-discharge plasma on metals

A layer-by-layer electron-microscope analysis has been made of the defect structure at different depths from an irradiation surface to establish the effect of a gas-discharge plasma on the metals Fe, Cu, and Mo and the alloy Ni₃Fe. A long-range effect has been established, namely, an increase in the scalar density of dislocations to depths of about 10 mm. The dislocation density increases with irradiation time, with approach to the irradiated surface, and with decrease of the yield point of the irradiated material. This effect depends nonmonotonically on the discharge voltage and the conditions of shielding of the samples. The types of the dislocasubstructures that are formed are similar to those formed in the case of plastic deformations.Translated from Izvestiya Vysshikh Uchebriykh Zavedenii, Fizika, No. 1, pp. 14–19, January, 1992.     

Elastic behavior of a screw dislocation in the wall of a hollow nanotube

The elastic behavior of a screw dislocation lying in the wall of a hollow cylindrical nanotube is studied theoretically. The corresponding boundary-value problem of the classical theory of elasticity is formulated and solved (for stresses) for a linear elastically isotropic or transversely isotropic body. The elastic energy of the nanotube with the dislocation and the image force exerted on this dislocation by the inner and outer nanotube surfaces are calculated. The internal space of the nanotube is shown to cause the following qualitative differences in the dislocation stress-field distribution: a change in the sign of stress-tensor components near the inner nanotube surface, a high stress concentration at this surface, and a strong stress gradient at this surface. The dislocation has only one position of unstable equilibrium in the nanotube wall, which is always shifted toward the inner nanotube surface. As the internal-space radius increases, the dislocation energy decreases and the position of its equilibrium shifts toward the outer nanotube surface; in the limiting case of a flat plate, it reaches the center of the plate. Near the nanotube free surfaces, the image force on the dislocation is large and can substantially affect the dislocation behavior.     

强流脉冲电子束作用下金属纯Cu的微观结构状态——变形结构

为了研究金属的超快变形机理,利用强流脉冲电子束(HCPEB)技术对多晶纯Cu进行了辐照处理,并利用透射电子显微镜对HCPEB诱发的表面微结构进行了表征.实验结果表明,HCPEB轰击多晶纯Cu后,在轰击表层诱发了幅值极大的应力和极高的应变速率.1次HCPEB轰击材料表层的变形结构以交滑移形成的位错胞和位错缠结结构为主;多次轰击后平行的位错墙和孪晶是该区域的主要变形结构特征;原子面的扩散乃至位错攀移可在晶界和孪晶界上形成台阶结构.根据各自区域的变形结构特征,对相应的变形机理进行了探讨. 关键词： 强流脉冲电子束 多晶Cu 变形结构 孪晶     

Effect of proton and laser irradiation on the elastic and inelastic properties of a V-Ti-Cr alloy

The behavior of Young’s modulus E and the decrement of ultrasonic vibrations δ in a V-4Ti-4Cr alloy is studied during proton (8-MeV protons, dose rate 10⁴ Gy/s) or IR laser (YAG: Nd³⁺ laser, wavelength 1.06 μm, intensity up to 10² W/cm²) irradiation. Measurements are performed using the method of a composite piezoelectric oscillator (longitudinal 100-kHz resonance vibrations). The sizes of the irradiated surface regions of a sample in the proton and laser experiments are the same in order to provide the same thermal conditions in the sample-quartz transducer system. The amplitude, time, and temperature dependences of E and δ are measured before and after preliminary plastic deformation, as well as before, during, and after irradiation of a sample. The process of postdeformation aging (the kinetics of recovery of internal friction after deformation) during proton irradiation is shown to differ substantially from that during laser irradiation. The specific features detected can be explained by the more intense evolution of the defect structure during proton irradiation. Analysis shows that radiation annealing is related to the ionizing component of proton irradiation, which excites the electronic subsystem of the metallic alloy and, thus, creates hot electrons and plasmons. The electron excitations relax at lattice defects (dislocations) and increase the dislocation mobility; this results in a relatively rapid decrease in the dislocation density and in a more significant (as compared to the laser irradiation) decrease in the level of internal stresses in the material. __________ Translated from Fizika Tverdogo Tela, Vol. 46, No. 8, 2004, pp. 1409–1415. Original Russian Text Copyright ? 2004 by Kardashev, Plaksin, Stepanov, Chernov.     

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.     

Dislocation density-based constitutive model for the mechanical behaviour of irradiated Cu

Performance degradation of structural steels in nuclear environments results from the formation of a high number density of nanometre-scale defects. The defects observed in copper-based alloys are composed of vacancy clusters in the form of stacking fault tetrahedra and/or prismatic dislocation loops that impede the motion of dislocations. The mechanical behaviour of irradiated copper alloys exhibits increased yield strength, decreased total strain to failure and decreased work hardening as compared to their unirradiated behaviour. Above certain critical defect concentrations (neutron doses), the mechanical behaviour exhibits distinct upper yield points. In this paper, we describe the formulation of an internal state variable model for the mechanical behaviour of such materials subject to these (irradiation) environments. This model has been developed within a multiscale materials-modelling framework, in which molecular dynamics simulations of dislocation–radiation defect interactions inform the final coarse-grained continuum model. The plasticity model includes mechanisms for dislocation density growth and multiplication and for irradiation defect density evolution with dislocation interaction. The general behaviour of the constitutive (homogeneous material point) model shows that as the defect density increases, the initial yield point increases and the initial strain hardening decreases. The final coarse-grained model is implemented into a finite element framework and used to simulate the behaviour of tensile specimens with varying levels of irradiation-induced material damage. The simulation results compare favourably with the experimentally observed mechanical behaviour of irradiated materials.     

Effect of dose on irradiation-induced loop density and Burgers vector in ion-irradiated ferritic/martensitic steel HT9

Samples of F/M steel HT9 were irradiated to 20?dpa at 420°C, 440°C and 470°C in a transmission electron microscope with 1?MeV Kr ions so that the microstructure evolution could be followed in situ and characterised as a function of dose. Dynamic observations of irradiation-induced defect formation and evolution were made at the different temperatures. Irradiation-induced loops were characterised in terms of their Burgers vector, size and density as a function of dose and similar observations and trends were found at the three temperatures: (i) both a/2 <111> and a <100> loops are observed; (ii) in the early stage of irradiation, the density of irradiation-induced loops increases with dose (0–4?dpa) and then decreases at higher doses (above 4?dpa), (iii) the dislocation line density shows an inverse trend to the loop density with increasing dose: in the early stages of irradiation, the pre-existing dislocation lines are lost by climb to the surfaces while at higher doses (above 4?dpa), the build-up of new dislocation networks is observed along with the loss of the radiation-induced dislocation loops to dislocation networks; (iv) at higher doses, the decrease of number of loops affects more the a/2 <111> loop population; the possible loss mechanisms of the a/2 <111> loops are discussed. Also, the ratio of a <100> to a/2 <111> loops is found to be similar to cases of bulk irradiation of the same alloy using 5?MeV Fe²⁺ ions to similar doses of 20?dpa at similar temperatures.     

高能电子辐照绝缘厚样品的表面电位动态特性

采用数值计算和实验测量相结合的方法, 阐明了高能电子束照射下绝缘厚样品的表面电位和电子产额动态特性. 结果表明: 由于电子在样品内部的散射和输运, 沿着深度方向, 空间电位先缓慢下降到最小值, 然后逐渐升高并趋近于零; 随着电子束照射, 样品的表面电位逐渐下降, 可至负千伏量级, 电子总产额逐渐增大至一个接近于1的稳定值; 电子束停止照射后, 长时间放置下, 表面电位将逐渐升高, 但带电并不会消除; 表面电位随电子束能量的升高近似线性下降, 随入射角的增大而升高, 而随样品厚度的增大仅略有下降.     

Electron microscope studies of the influence of electrons with subthreshold energies on the formation and annealing of structural defects in ZnTe and CdZnTe

The influence of subthreshold-energy electrons on the formation and annealing of structural defects in ZnTe and on the annealing of dislocation loops preinjected in the sample by bombardment with argon ions is investigated by transmission electron microscopy. The final form and density of structural defects formed after electron irradiation is observed to depend on the total electron flux, whereas the rate of formation of defects and annealing of dislocation loops increases linearly with the intensity of electron irradiation. A comparison is drawn with CdZnTe, Si, and GaAs irradiated under similar conditions. The results are attributed to subthreshold defect nucleation mechanisms.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 111–115, January, 1996.     

X-ray measurement of a microdistortion tensor and its application in an analysis of the dislocation structure of thick GaN layers obtained by hydrochloride gaseous-phase epitaxy

The method of two-and three-crystal x-ray diffractometry (TCD) is used for studying the dislocation structure of thick GaN layers grown by chloride gaseous-phase epitaxy (CGE) on sapphire, as well as on a thin GaN layer, which is grown by the metalloorganic synthesis (MOS) method. Five components of the microdistortion tensor 〈?_ij〉 and the sizes of the coherent scattering regions along the sample surface and along the normal to it are obtained from the measurements of diffracted intensity in the Bragg and Laue geometries. These quantities are used to analyze the type and geometry of the dislocation arrangement and to calculate the density of the main types of dislocations. The density of the vertical screw dislocations, as well as of the edge dislocations, decreases (by a factor of 1.5 to 3) during growth on a thin GaN layer. The diffraction parameters of the thick layer on the MOS-GaN substrate suggest that it has a monocrystalline structure with inclusions of microcrystalline regions.     

Dislocation vs. production bias revisited with account of radiation-induced emission bias. I. Void swelling under electron and light ion irradiation

Early experimental data on void swelling in electron-irradiated materials disagree with the dislocation bias models based on the dislocation-point defect elastic interactions. Later, this became one of the factors that prompted the development of models based on production bias (PBM) as the main driver for swelling, which assumed that the dislocation bias was much lower than that predicted by theoretical analyses of dislocation bias. However, the PBM in its present form fails to account for important and common observations, namely, the indefinite void growth often observed under cascade irradiation and the swelling saturation observed under high-dose irradiation and in void lattices. In this paper, we show that these contradictions can be naturally resolved in the framework of the rate theory that accounts for the radiation-induced vacancy emission from extended defects, such as voids, dislocations and grain boundaries. This modification introduces a new bias type in the theory, namely, the emission bias. This modified rate theory agrees well with the experimental data and demonstrates that the original dislocation bias should be used in rate theory models along with the emission bias in different irradiation environments. The modified theory predictions include, but are not limited to, the radiation-induced annealing of voids, swelling saturation under high-dose irradiation, generally, and in void lattices, in particular.     

Defect concentration profiles near the surface in nickel irradiated with 2 MeV electrons

Abstract

In the next nearest surface region the vacancy concentration is constant and independent of the irradiation temperature between 750 and 300°C and decreases with increasing electron flux. The conentrations of interstitials and of vacancies in the sink-free bulk of the material are equal and depend on the irradiation temperature, and are almost independent of the irradiation flux. The activation migration energies of vacancies and of interstitials decrease with increasing irradiation flux.It is further shown that the dynamic steady state defect concentrations resulting from the rate equations are artificial concentrations, which will not be achieved in finite times.     

强流脉冲电子束辐照诱发金属纯镍中的空位簇缺陷

利用强流脉冲电子束(high-current pulsed electron beam,HCPEB)技术对多晶纯Ni进行了辐照处理,采用透射电子显微镜详细分析了辐照诱发的缺陷结构.HCPEB辐照后,纯镍表层积聚了幅值极大的残余应力,沿{111}晶面形成了稠密的位错墙及孪晶结构,另外还形成了大量的包括位错圈、堆垛层错四面体(SFT)及孔洞在内的空位簇缺陷.SFT缺陷的数量远高于其他空位簇缺陷,其周围区域位错密度很低.孔洞缺陷主要出现在SFT密集区域.HCPEB瞬间的加热和冷却诱发的幅值极大的应力和极高的应变 关键词： 强流脉冲电子束 多晶纯Ni 空位簇缺陷 堆垛层错四面体     

超临界水冷堆燃料包壳材料的辐照损伤研究进展

超临界水冷堆（SCWR）是第四代核电站的主力堆型之一,高温、高压、超临界水环境下的辐照损伤问题是其燃料包壳材料面临的最大挑战。SCWR燃料包壳候选材料主要包括锆合金、奥氏体不锈钢、铁素体/马氏体不锈钢、镍基合金、ODS合金五大类,奥氏体不锈钢是最有希望的候选材料。介绍了近年来在这个领域国际上的主要研究进展。作者所在团队也对多种SCWR的候选材料进行了辐照损伤研究,包括:镍基合金C-276和718、铁素体/马氏体钢P92、奥氏体不锈钢AL-6XN和HR3C。对AL-6XN的氢离子辐照实验发现,辐照产生的缺陷主要是间隙型位错环,伯格斯矢量为1/3<111>,在较高剂量（5～7 dpa）辐照下,出现空洞肿胀。在氢滞留的影响下,位错环有着独特的演化规律,总结提出了位错环的四阶段演化过程。The Supercritical Water-cooled Reactor (SCWR) is one of the prior Generation IV advanced reactors. Irradiation damage is one of the key issues of fuel cladding materials which will suffer serious environment, such as high temperature, high pressure, high irradiation and supercritical water. The candidate materials contain zirconium alloys, austenitic stainless steels, ferritic/martensitic stainless steels, Ni-base alloys and ODS alloys. Austenitic stainless steels are the most promising materials. This paper summarized the international researches on irradiation effects in fuel cladding materials for SCWR. The group of authors also has done many researches in this field, including nickel-base alloy C-276 and 718, ferritic/martensitic steel P92 and austenitic stainless steel AL-6XN and HR3C. In AL-6XN austenitic stainless steels irradiated by hydrogen ions, dislocation loops were the dominant irradiation defects. At higher irradiation dose (5～7 dpa), the voids were found. All the dislocation loops were confirmed to be 1/3<111> interstitial type dislocation loops, and four evolution stages of dislocation loops with hydrogen retention were suggested.