Microplastic deformation of polycrystalline and submicrocrystalline titanium during static and cyclic loading

A study is made of the laws governing the accumulation of microplastic strain during the static and cyclic loading of polycrystalline and submicrocrystalline titanium. It is shown that a change from the polycrystalline structure to the submicrocrystalline structure does not change the character of development of microplastic strain for either type of loading, but it does increase fatigue strength and fatigue limit. A correlation between the fatigue strength based on 10⁶ cycles and the macroscopic elastic limit was found to exist for both types of loading. Siberian Physico-Technical Institute (at Tomsk University), Institute of the Physics of Strength and Materials Science (in the Siberian Division of the Russian Academy of Sciences), and the Institute of the Physics of Promising Materials (at Ufa State University of Aeronautical Engineering). Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 41, No. 12, pp. 20–25, December, 1998.     

Thermally stimulated acoustic splitting of an elastic wave in polycrystalline niobium subjected to electron-beam remelting

The effect of temperature on the Young’s modulus of electron-beam-remelted polycrystalline niobium is studied in the temperature range 20–1000°C. The impurity content in the material is Ta<0.5 wt% and O₂<0.1 wt%. The acoustic split of the resonant frequency is found in the temperature range 60–180°C, which makes the determination of the Young’s modulus uncertain. Mechanisms behind the thermally stimulated splitting of an elastic wave and the behavior of the Young’s modulus over a wide temperature interval are discussed.     

强流电子束无箔二极管结构设计与特性研究

 主要叙述高功率二极管的理论模型和结构设计,采用基于引导磁场和相对论近似情况下的空间电荷限制流模型,对磁浸没无箔二极管产生的空心相对论电子束进行了动态数值模拟,研究了二极管几何结构及引导磁场对二极管束流特性的影响。     

毛细管放电X光激光装置中的预脉冲电源

针对目前毛细管放电X 光激光装置产生的预脉冲电流幅值过大、持续时间较短的问题，提出了增加预脉冲开关抑制原有预脉冲，再外加由脉冲成形网络组成的预脉冲发生器，产生所需预脉冲的改造方案。可在主脉冲来临之前产生幅度10~50A，持续时间约17μs的方波预脉冲电流，来满足毛细管放电泵浦类氖氩X光激光实验的需要。     

激光辐照下充压圆筒变形的相似律问题

以充压圆筒在强激光辐照下的变形与破坏响应为研究目标,首先利用相似分析方法,主要采用了方程分析法和量纲分析法,确定了相似准则。然后利用ANSYS有限元程序,模拟了三组几何和物理相似的大小模型。通过对计算结果的分析表明,满足相似准则的大小模型,在相应的时间和空间,相对的物理参量是一致的。     

激光辐照下充压圆筒变形的相似律问题

 以充压圆筒在强激光辐照下的变形与破坏响应为研究目标,首先利用相似分析方法,主要采用了方程分析法和量纲分析法,确定了相似准则。然后利用ANSYS有限元程序,模拟了三组几何和物理相似的大小模型。通过对计算结果的分析表明,满足相似准则的大小模型,在相应的时间和空间,相对的物理参量是一致的。     

Microplastic deformation of polycrystals during cyclic loading

A model of microplastic deformation of polycrystals during zero-start cyclic loading with tensions lower than the yield strength is proposed according to which during cycling, thermally activated movement of dislocations occurs under conditions of stress relaxation. Based on this model and the statistical theory of polycrystalline microdeformation, the accumulation of microplastic deformation is theoretically described as a function of the number of loading cycles and the stress amplitudes. It is theoretically proved that in the cycling process the microplastic deformation that accumulates over one cycle decreases as the number of cycles increases; up to the macroscopic elastic limit it is independent of the stress amplitude, and then sharply increases. Agreement of the theory with experimental data for spring alloys is observed in the density of mobile dislocations, which decreases during cycling.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 29–34, March, 1990.     

强流短脉冲电子束束剖面测量技术

 束流剖面信息的获得对于加速器的研究有着重要的意义。对强流短脉冲电子加速器束剖面测量技术作了评述。目前,发展时间分辨的快响应的光学测量技术及实时在线测量为主要发展趋势。     

Optical properties of polycrystalline alumina after irradiation with iron ions and annealing

Optical absorption of polycrystalline corundum (polycor) after irradiation with iron ions and subsequent annealing in vacuum was studied. It was found that substitutional, intrinsic radiation, biographical defects, and complexes on their basis have an effect on the absorption parameters and optical transitions between localized states and allowed bands. The contributions to changes in the optical properties of individual substitutional defects, their clusters, and complexes with the participation of substitutional defects and radiation defects were singled out. The influence of defects and iron oxides formed upon annealing on absorption was estimated. The most proable nature of clusters of substitutional defects and impurity-vacancy complexes was identified.     

强流短脉冲电子束束剖面的时间分辨测量

介绍了一套基于切伦科夫辐射的、用于强流短脉冲电子束束剖面测量的装置。装置利用扫描相机记录背面打毛的石英玻璃薄片中产生的切伦科夫光信号。使用该装置,在中国工程物理研究院流体物理研究所的2MeV注入器上进行了切伦科夫光的验证实验和时间分辨的束剖面测量实验。分析表明,测量系统的时间分辨率和空间分辨率分别为1.75ns和0.74mm。     

Ultrasonic amplification semiconductors subjected to deformation

It is shown that in semiconductors with inherent piezo-effect or high relative dielectric permittivity (?_rel ? 10³) which have undergone uniaxial deformation an additional electron-phonon interaction is possible, this being conditioned by the non-linear deformation piezo-effect or electrostriction. The non-linear piezo-module in CdS and the electrostriction constant of the second order in SrTiO₃ have been experimentally investigated.Additional ultrasound amplification conditioned by deformation can exceed the amplification in a non-deformed semiconductor by one order.     

Electrical properties of nanocomposites subjected to deformation

The electrophysical properties of a new type of nanocomposites are considered. In these materials, the metallic granules are distributed in a rubberlike matrix. Nanocomposites exhibit either metallic or hopping conduction, depending on the bulk concentration of the metallic granules. The effect of pressure (for hydrostatic compression and for uniaxial deformation) upon the resistance of such composites is studied in both conduction regimes. The practically important extremely strong dependence of their resistance upon pressure in the hopping conduction regime is a consequence of the exponentially strong dependence of the probability of intergranule electron tunneling on the distance between the granules.     

Optimal deformation and ion irradiation modes for production of a uniform submicrograin structure in molybdenum

Transmission and scanning electron microscopy have been used to investigate the structure of molybdenum after complex processing: deformation and irradiation with accelerated argon ion beams. The analysis of the effect of deformation and radiation parameters on the structural transformations and mechanical properties of molybdenum allowed us to find the optimal mode of processing to form a submicrograin uniform-in-size structure.     

Low-field electrodynamics of polycrystalline ternary molybdenum chalcogenides

The penetration of very weak magnetic fields into the polycrystalline low-temperature superconductor SnMo₆S₈ is studied experimentally. The experimental results agree satisfactorily with the theory of the critical state in the framework of low-field electrodynamics. It is found that the critical current density in this case does not depend on the dc magnetic field. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 3, 184–188 (10 February 1999)     

Sub-ps pump and probe photoemission from polycrystalline molybdenum

Pump and probe electron photoemission, induced by 150 fs–790 nm laser pulses on polycrystalline molybdenum, is used to investigate the non-linear photoemissive regime. The analysis of these experimental data evidences third and fourth order thermally assisted currents that contribute to the electron yield. In addition, partial yield measurements at very low pulse intensities confirm the above analysis, evidencing a change in the logarithmic slope as predicted by the theory.     

Cyclic deformation of polycrystalline Cu films

Fatigue impairs the reliability of macroscopic metallic components utilized in a variety of technological applications. However, the fatigue behaviour of thin metal films and small-scale components used in microelectronics and mechanical microdevices has yet to be explored in detail. The fatigue behaviour in submicrometre thin films is likely to differ from that in bulk material, since the volume necessary for the formation of dislocation structures typical of cyclic deformation in bulk material is larger than that available in thin films. The thin-film dimensions and microstructure, therefore, affect the microscopic processes responsible for fatigue. The fatigue behaviour of Cu films 0.4, 0.8 and 3.0 µm thick on polyimide substrates was investigated. The specimens were fatigued at a total strain amplitude of 0.5% using an electromechanical tensile-testing machine. This work focuses on the characterization of fatigue mechanisms and the resulting fatigue damage of thin Cu films. Extrusions similar to those observed in bulk material were found at the film surfaces after cyclic loading. Voids observed beneath the extrusions, close to the film-substrate interface, contributed significantly to thin-film failure. Thinner films were more fatigue resistant and contained fewer and smaller extrusions than thicker films did. A small thickness appears to inhibit void nucleation. This observation is explained in terms of vacancy diffusion and annihilation at free surfaces or grain boundaries. Transmission electron microscopy investigations confirmed that no long-range dislocation structures have developed during fatigue loading of the films investigated.