位错芯区扩散引起的非线性滞弹性内耗峰

若干年来,我们对于出现在Al-Cu和Al-Mg系中的表现正常和反常振幅效应的坐落在室温附近的内耗峰进行了系统研究,测得的激活能接近于溶质原子在位错管道中扩散的激活能，从而认为内耗峰的基本过程是溶质原子在隹错芯内的扩散，并且提出了根据位错弯结模型的物理图像。在70年代，Windler-Gniewek等根据弦模型对于位错芯内的扩散进行了理论计算，推导出描述内耗行为的数学表达式与我们的实验结果有许多相似之处。本文对于弦模型和弯结模型进行了对比，分析了位错芯内的纵向扩散和横向扩散所引起的内耗的非线性表现以及内耗峰温和峰高随着应变振幅和测量温度而变化的情况，进一步了我们发现的室温非线性内耗峰（非线性滞弹性内耗）是由于溶质原子在位错芯内扩散所引起的。 关键词：     

晶界弛豫研究50年

文章综述了我国科学工作者５０年来关于晶界弛豫研究的早期开拓和近期发展．前者包括扭摆内耗仪的发明、晶界内耗峰的发现和无序原子群晶界模型的提出．后者包括澄清了关于晶界内耗峰来源的争论,揭示了晶界弛豫具有一个临界温度,从而提出了一个适合于各种温度的综合的晶界模型．一个最重要的进展是关于竹节晶界内耗峰的发现与其机理的阐明,从而揭示了晶界附近的位错亚结构能够影响晶界本身的性质和结构．这对于研究多晶金属的力学性质提供了一个广阔的途径．另外,晶界与邻域位错的非线性交互作用的发现,为奠定非线性滞弹性这门新学科提供了实验基础     

饱和砂岩的滞弹性弛豫衰减特征及微观机理的探索

应用Metravib热机械分析仪,以饱和岩石进行正弦波加载的方式, 分别对三种不同孔隙度的泵油饱和彭山砂岩、泵油和甘油饱和自贡长石砂岩进行了衰减实验研究,得到衰减的热弛豫规律.据此规律求得它们的激活能和原子振动频率, 其激活能和原子的振动频率比间隙原子的激活能和振动的频率低, 此现象用饱和砂岩中产生的缺陷原子簇的整体振动比单个或孤立的原子的振动频率低做出了解释. 在饱和岩石的晶粒间界缺陷处参与扩散的是固体原子、液体及气体原子. 并得出随孔隙度和黏滞系数增大,衰减强度和激活能增大,原子的振动频率增高,弛豫时间减小的结论. 在正弦波应力作用下,由多种矿物晶体胶结而成的饱和砂岩是一种多晶、多相的固体, 由于内部结构复杂、缺陷广布,产生弛豫衰减是普遍现象.砂岩中存在点缺陷、位错、 晶界及孪晶界面等许多缺陷及缺陷间的相互作用都可以产生弛豫型衰减峰. 用饱和砂岩中特有的饱和液体及砂岩内部结构的复杂性解释了饱和砂岩的衰减机理, 很自然地将其宏观衰减特征与微观结构紧密连在一起.饱和砂岩中的各种缺陷、 相界等会导致多重弛豫,使它们的弛豫衰减峰变宽,分布参数增大.这项研究既具有理论意义,也具有实用价值.     

高剂量离子注入形成的非晶层重新结晶过程中杂质外扩散的物理模型

本文提出了一个杂质沉淀引起位错生成、位错-杂质相互作用、杂质原子沿晶粒间界快速扩散的模型,用以解释高剂量离子注入形成的非晶层在重新结晶的退火过程中杂质外扩散和缺陷运动现象。给出了在位错的合应力场的影响下杂质的扩散方程。以能量为80keV,剂量为10¹⁶cm^-2的Pb⁺注入Si(111)面为例,对扩散方程进行了数学物理处理,从而给出了根据实验测量推演表观扩散系数随时间变化及位错的合应力场对杂质的作用力的纵向分布的方法。实验测得的位错合应力场对杂质的作用系数α≈8.4×10^-28dyn·cm³,退火时间在5×10³sec至8.25×10³sec内,表观扩散系数D随时间的变化为一指数关系。 关键词：     

La2 NiO4+δ体系相分离现象的低频内耗研究

La2 NiO4 δ体系额外氧δ =0 .0 71,0 .110 ,0 .135 ,0 .14 0样品中存在着一个间隙氧弛豫运动引起的低频内耗峰 ,其内耗峰峰位置随额外氧的增多向高温移动 .而额外氧处于其间位置δ =0 .0 87样品中则出现了两个弛豫型内耗峰 ,分析认为它们源于体系相分离后形成的不同一维有序结构中间隙氧的跳跃 .此外 ,额外氧δ=0 .0 38样品中也观察到两个弛豫型内耗峰 ,其中低温峰性质与上相同 ,而高温内耗峰则可能对应于体系相分离后形成的低温四方相中氧原子的跳跃弛豫     

不同加载条件下位错和溶质原子交互作用的数值模拟

动态应变时效,即位错和溶质原子的动态交互作用,对合金材料的力学性质产生重要影响. 本文基于蒙特卡罗方法,建立了“多位错-溶质原子” 二维动力学模型,分别模拟了单位错-恒定应力率、多位错-无应力、多位错-恒定应力和多位错-恒定应力率四种条件下位错和溶质原子的演化过程. 单位错-恒定应力率情况下,低应力率时位错被溶质原子钉扎而无法脱钉,高应力率时位错未被钉扎而一直运动,只有在适当应力率范围内,位错才呈现出反复的钉扎和脱钉;多位错-无应力时,溶质原子向正/负位错的下/上方偏聚;多位错-恒定应力时,位错运动受溶质原子钉扎的影响随应力增大而减小;多位错-恒定应力率时,集群化的钉扎和脱钉过程导致了位错总位移呈现阶梯状的演化. 模拟结果表明：“位错-溶质原子”尺度上呈现了动态应变时效微观过程,与其理论描述相一致. 关键词： 动态应变时效 动力学模型 位错运动     

钨中不同构型的双自间隙原子扩散行为研究

钨作为一种重要的核材料,在辐射环境下的微观演化行为与自间隙原子缺陷的扩散行为密切相关.研究不同构型自间隙原子的扩散行为有助于全面理解材料的微观演化过程.本文采用分子动力学方法重点考察了钨中具有不同构型的双自间隙原子随温度变化的扩散行为.结果表明:彼此互为最近邻的111双自间隙原子,随着温度的升高,从一维扩散演变成三维扩散,在111方向保持稳定的最近邻结构;次近邻111双自间隙原子在一定温度范围内沿111方向一维扩散,当温度高于600 K将解离成两个独立运动的自间隙原子;而三近邻结构在温度高于300 K就将解离.非平行结构的双自间隙原子在一定温度范围内形成固着性结构,几乎不移动,但在温度高于1000 K时将转化成移动性缺陷.通过将微动弹性带算法获得的自间隙原子迁移能与阿伦尼乌斯关系拟合的结果进行对比,表明了钨中单自间隙原子和双自间隙原子的扩散系数随温度的变化规律不适于用阿伦尼乌斯关系来描述,而线性关系则能合理地描述这一规律.     

晶界驰豫研究50年

文章综述了我国科学工作者５６０年来关于晶界驰豫研究的早期开拓和近期发展,前者包括扭摆内耗仪的民昌界内耗峰的发现和无序原子群晶界模型的提出,后者包括澄清了关于介内耗峰来源的争论,揭示限晶界弛豫具有一个临界温度,从而提出了一个适合于各种温度的综合的晶界模型,一个最重要的进展是关于竹节晶界内耗峰的发现与其机理的阐明,从而揭示了介附近的位错亚结构能够影响晶一身性质和结构,这对于研究多晶金属的力学性质提供了     

扩展位错低频内耗的模型

本文提出面心立方合金中扩展位错引起低频内耗峰的一个模型,用来解释高浓度Cu-Al和Cu-Zn合金经过冷加工后在210K附近出现的弛豫型内耗峰(测量频率约为1Hz)。文中指出,扩展位错在外力作用下的运动,可以分解为相对运动(两个部分位错之间的相对位移)和整体运动(扩展位错中心的位移)。除了考虑两个部分位错之间交互作用引起的回复力和位错线张力引起的回复力以外,本文引入了邻近位错之间长程交互作用引起的回复力,并且论证了这种回复力只影响扩展位错的整体运动,但不影响其相对运动。扩展位错的相对运动和整体运动,分别导致相对运动内耗峰和整体运动内耗峰。二者峰温相近。实验上观察到的内耗峰是这两个内耗峰的叠加。本文模型的推论与实验结果相符。 关键词：     

能量粒子轰击金刚石的计算机模拟

利用Tersoff势和分子动力学方法研究了初始动能为500 eV的硼粒子注入金刚石的微观行为.结果表明：硼注入后产生温度为5000 K的热峰，其寿命为0.18 ps；同时产生半径为0.45 nm局部非晶化区域，三重配位原子数占该区域原子数的7%.薄膜表层原子向内弛豫，近表层原子向外弛豫，表面层与近表层原子的间距减少了15%，表面层表现为压应力.硼原子以B<110>分裂间隙的形式存在于金刚石结构中. 关键词： 分子动力学模拟 金刚石 硼 注入     

Internal-friction study of the interstitial–substitutional effect on the deformation behaviour of Nb–O,Nb–Ta–O and Nb–Mo–O single crystals

To investigate the interstitial-substitutional interaction in dislocations, the effect of 0 on the temperature, frequency and amplitude dependence of the internal friction Q ^?1 in Nb–O, Nb-20 mol% Ta–O and Nb-20 mol% Mo–O single crystals has been studied (f = 1.55–8.2 Hz) in the temperature range from 298 to 1473 K. In our previous study, Nb–Mo and Nb–Ta single crystals were found to be strengthened by solute O. It was also suggested that the interstitial–substitutional interaction in dislocations contributes to the increase in their critical resolved shear stress (CRSS). In this study, Snoek-type relaxation peaks due to O are observed between 500 and 700 K in all the single crystals. The Snoek peak of Nb-20mol% Mo–O consisting of several peaks is analysed. The activation energy of the Snoek peak in Nb-20mol% Mo–O is higher than that of Nb–O. These results are attributable to the existence of the interstitial–substitutional complexes. The amplitude dependence of Q ^?1 at intermediate and high temperatures decreases as the O content increases. Moreover, the breakaway stress of Nb-20 mol% Mo–O still has a high value at 1200K and does not decrease much even at 1473 K. This suggests that the formation of Mo–O complexes reduces the dislocation mobility at high temperatures. From the results, the effect of the interstitial-substitutional interaction on the CRSS was discussed.     

硅中位错增殖的实验观察

用化学侵蚀法研究了在机械应力和热应力作用下硅中位错的增殖和非均匀成核。结果表明,在使位错增殖和成核作用上,热应力同机械应力是等效的。硅中小角晶界中的位错,原生孤立位错都能成为位错源;晶体内部的缺陷及表面蚀斑处的应力集中能够引起位错成核;硅中螺型位错能够通过交叉滑移机制发生增殖。对新生位错环空间分布的研究表明,Frank-Read机制可能是位错增殖的主要形式。位错能否发生增殖,主要决定于位错源所受分切应力的数值、晶体温度、位错本身的结构特点以及钉扎情况等。     

The influence of intrisic defects on the degradation and luminescence of GaAs and other III–V compounds

A significant contribution to the degradation of GaAs-based lasers and light-emitting diodes arises from the formation of so-called dark line defects. It is shown that these defects are accumulations of non-radiative recombination centres around dislocations. The centres are identified as As vacancies, which are emitted by climbing dislocations, concomitantly with the absorption of Ga interstitials. From scanning deep-level transient spectroscopy observations it is concluded that the so-called DX centres are Ga interstitials. The driving force for dislocation climb and thus for dark-line-defect formation is a supersaturation of Ga interstitials originating from the growth of the GaAs crystals under Ga-rich conditions as a consequence of the high volatility of As. Phenomena in other III–V compound semiconductors related to the formation of dark line defects in GaAs are also discussed.     

In situ investigation of the effect of a magnetic field on the mobility of dislocations in deformed KCl:Ca single crystals

This paper presents the results of an experimental investigation into the mobility of edge dislocations in KCl:Ca single crystals and the effect of a static magnetic field of 0.3 T on the dislocation mobility. The experiments on the effect of a magnetic field on the dislocation mobility were carried out with the use of a high-resolution (1 ms) method that permits in situ measurements of the sample dipole moment induced by the motion of charged dislocations as the crystal is being deformed. It is found that the starting stress is reduced in a magnetic field and the activation volume for overcoming of point defects by the dislocations is increased. It is further found that the magnetic field increases the rate of motion of the dislocations at the initial stage of deformation (to the point of dislocation multiplication) but has no effect on the mobility in the multiplication stage. Fiz. Tverd. Tela (St. Petersburg) 39, 630–633 (April 1997)     

Specific features in the generation and motion of dislocations in silicon single crystals doped with nitrogen

The specific features in the generation and motion of dislocations are investigated in Si: N single crystals grown by the Czochralski method. The motion of dislocation loops is analyzed by the four-point bending technique in the temperature range 500–800°C. The dislocation loops are preliminarily introduced into the samples with the use of a Knoopp indenter at room temperature. It is found that doping with nitrogen leads to a considerable increase in the critical stress of the onset of dislocation motion from surface sources (indentations) and in the stress of the generation of dislocations from internal sources. The velocity of dislocation motion in Si: N crystals is less than that in undoped crystals (under comparable loads). The hardening effect of nitrogen is explained by the fact that nitrogen promotes the decomposition of a solid solution of oxygen in silicon during postcrystallization cooling.     

On the mechanism of the electric field effect on dislocation mobility in alkali-halide crystals

The dependence is investigated of the velocity of motion of edge and screw dislocations on the applied shear stress in annealed and quenched NaCl and KC1 crystals with various impurity content under the action of an electric field of up to 50 kV/cm. It is shown that in impure crystals the action of the field is determined by its effect on damping centers, while in pure crystals, by its effect on charged dislocations. The interaction force of an edge dislocation with impurity-vacancy dipoles of various orientation is calculated. The charge density and sign of a dislocation is estimated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 16–21, May, 1975.     

Mobility of edge and screw dislocations in γ-irradiated LiF crystals

The free path lengths of ensembles of edge and screw dislocations in the stress field of a concentrated load are studied in γ-irradiated LiF crystals. The relative mobility of edge and screw dislocations is found to depend substantially on the irradiation dose and temperature. The results obtained are discussed in the context of additional retardation of screw dislocations with dislocation debris that appears during double cross slip.     

Different types of dislocation dynamics resulting from the dynamic aging of dislocations

The effect of mobile impurities on the dislocation dynamics under static and variable loading of crystals is calculated. It is shown that the dynamic aging of dislocations may produce a specific regime where dislocations are at rest upon static loading and move only under a growing stress. The dislocation mobility in this regime is athermal. The existence conditions for this regime are studied. The dependence of the dislocation path lengths in silicon on the stress pulse rise time that is observed in pulsed-load experiments is explained by the existence of this regime.     

GENERALIZATION OF ESHELBY'S METHOD TO THE ANISOTROPIC ELASTICITY THEORY OF DISLOCATIONS IN QUASICRYSTALS

The general expressions of the elastic fields induced by straight dislocations in quasicrystals have been given according to Eshelby's method which was used to treat the anisotropic elasticity of dislocations in crystals. As an example, the elastic displacement vector, the stress tensor and the elastic energy density of a screw dislocation line lying on the quasiperiodic plane of decagonal quasicrystals are calculated.     

GENERALIZATION OF ESHELBY''S METHOD TO THE ANISOTROPIC ELASTICITY THEORY OF DISLOCATIONS IN QUASICRYSTALS

The general expressions of the elastic fields induced by straight dislocations in quasicrystals have been given according to Eshelby's method which was used to treat the anisotropic elasticity of dislocations in crystals. As an example, the elastic displacement vector, the stress tensor and the elastic energy density of a screw dislocation line lying on the quasiperiodic plane of decagonal quasicrystals are calculated.