强脉冲磁场冲击处理对铝基复合材料塑性的影响机制

铝基复合材料在加入颗粒相之后, 延伸率和塑性变形能力明显降低. 为改善其塑性变形能力, 通过对比强脉冲磁场冲击处理前后试样内部组织和残余应力的变化特征, 研究了磁致塑性效应对铝基复合材料塑性变形能力的影响机理. 结果表明: 当磁感应强度从2 T变化到4 T时, 铝基复合材料中位错密度显著增加, 4 T时的位错密度是未加磁场时的3.1倍; 3 T, 30个脉冲处理后的复合材料中残余应力值从未加磁场时的41 MPa减小为-1 MPa. 从原子尺度来看, 强磁场导致了磁致塑性效应, 从而引起了位错的运动, 并促进了位错的退钉扎和可移动位错数量的增加; 从材料内部整体结构变化来看, 磁场加速了材料内应力的释放速率, 降低了材料内部的残余应力, 从而改善了铝基复合材料的塑性变形能力.     

Effect of magnetic field pulses on the anelastic properties of nitrogen-containing steel

The effect of weak magnetic field pulses on the dynamic properties of dislocations interacting with impurity-defect complexes is determined by the internal-friction method. The effect is characterized by an increase in the plasticity of a material under the conditions of microplastic deformation and slowing of strain hardening. Zh. Tekh. Fiz. Zh. Tekh. Fiz. 69, 122–123 (August 1999)     

Possibilities for using a pulsed magnetic field to influence structural states in oxide glass

The structural-energy spectrum of the states of a bismuth-containing oxide glass, the sensitivity of these states to the action of a pulsed magnetic field, and the thermodynamic and kinetic stability of the structure excited by a pulsed magnetic field are studied by the method of measuring the internal friction. It is established that a pulsed magnetic field influences the structural states and that this leads to irreversible changes in the structure and the crystallization parameters of the glass. It is found that the efficacy of acting on a material with a pulsed magnetic field also depends on the parameters of the field and the structural-energy state of the material and that the action itself is of a thermally-activated relaxational character. The optimal conditions for the action of a pulsed magnetic field on glass are determined. Zh. Tekh. Fiz. 68, 50–54 (October 1998)     

Magnetically stimulated hardening of NaCl(Pb) crystals

Dislocation motion in NaCl(Pb) crystals under a pulsed mechanical load with and without a magnetic field is investigated. It is found that the dislocation mobility decreases when these crystals are deformed in a magnetic field. It is inferred that the observed magnetically stimulated hardening of NaCl(Pb) is due to a characteristic feature of spin-dependent electronic transitions in the dislocation-lead impurity system which increase the barrier for dislocation motion. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 3, 226–228 (10 August 1999)     

激光冲击690高强钢位错组态与晶粒细化的实验研究

为研究激光冲击材料内部位错组态和晶粒细化的关系,用脉冲激光对690高强钢试样进行了冲击强化处理,采用扫描电镜和透射电镜分别获得了冲击后试样的扫描电子显微像和透射电子显微像、高分辨电子显微像,并对高分辨电子显微像进行快速傅里叶逆变换,从位错组态角度建立了激光冲击690高强钢晶粒细化模型.结果表明,690高强钢试样经功率密度为5.09 GW/cm^2的激光冲击加载后,其材料内部位错增殖、表层晶粒细化,截面晶粒尺寸大小分布在80~200 nm;析出相与基体保持半共格关系,基体中分布着众多刃型位错、位错偶以及扩展位错等缺陷,其中位错偶是由带割阶的螺型位错运动形成;通过由位错、扩展位错、空位等构成的几何位错界面扩展交汇把原始大晶粒分割成细小晶粒;激光冲击690高强钢晶粒细化模型可以描述激光冲击690高强钢位错运动主导的晶粒细化过程.     

Dislocations used to probe the defect state of an ionic crystal lattice excited by a pulsed magnetic field

This paper presents the results of an investigation into the effect of a pulsed magnetic field on the state of linear and point defects in ionic crystals. For different amplitudes (1–7 T) and pulse lengths (3×10⁻⁵ to 10² s) of the pulsed field the kinetics of the transformation of defects into a new state and their relaxation after the field is turned off are studied in the temperature range 77–400 K. It is found that the relaxation of the states of point defects is mainly through recombination, and the change of state of the dislocations and of the point defects contribute nonadditively to the change in the dislocation mobility. The exposure of the crystal to a magnetic field leads to an increase in the dislocation mobility when the sample is mechanically stressed and to a decrease in the dislocation displacement with a second field pulse. Fiz. Tverd. Tela (St. Petersburg) 39, 634–639 (April 1997)     

Electrically stimulated motion of dislocations in a constant magnetic field

This paper reports on the results of investigations into the dislocation mobility in n-Si single crystals (N _d =5×10²⁴ m^?3) upon simultaneous exposure to electric (j=3×10⁵ A/m²) and magnetic (B≤1 T) fields. It is found that the introduction of dislocations (≈10⁹ m^?2) into dislocation-free silicon doped with phosphorus leads to the appearance of the paramagnetic component of the magnetic susceptibility. The paramagnetic component increases with an increase in the dopant concentration. Similar transformations in silicon account for the formation of magnetically sensitive impurity stoppers that respond to external magnetic perturbations. An analysis of the behavior of dislocations in electric and magnetic fields has revealed a parabolic dependence of the dislocation path length on the magnetic induction B. The effective charges and mobilities of dislocations are numerically calculated from the results obtained. A model is proposed according to which the observed increase in the dislocation mobility is associated with the decrease in the retarding power of magnetically sensitive stoppers due to a local change in the magnetic characteristics of the material and the spin-dependent reactions stimulated by a magnetic field.     

Dynamics of surface dislocation ensembles in silicon under conditions of mechanical and magnetic perturbations

This paper reports on the results of investigations into the dynamics of surface dislocation ensembles in silicon under conditions of mechanical and magnetic perturbations. The motion of defects is described with due regard for barriers of three types, including magnetically sensitive point defects and dislocations. Within the concept of spin-dependent reactions between structural defects, a kinetic model is proposed for the magnetic-field-stimulated changes observed in the dislocation mobility due to the formation of long-lived complexes involving paramagnetic impurities. It is experimentally proved that the preliminary treatment of dislocation-containing crystals in a magnetic field (B=1 T) for 5–45 min leads to an increase in the velocity of dislocations in n-Si and p-Si samples by factors of two and three, respectively. The magnetic memory effect is observed in dislocation-containing silicon crystals. Consideration is given to the decay kinetics of the magnetic memory during storage of the silicon samples under natural conditions after magnetic treatment. The basic quantitative characteristics of the motion of linear defects in a magnetic field (for example, the partial velocities of dislocations, the dynamics of dislocation segments at stoppers of different types, and the expectation times for the appearance of the appropriate stoppers) are determined by fitting the experimental data to the theoretical results.     

Dislocation-induced internal friction of a material with vacancies in weak magnetic field pulses

It is found that the form of the amplitude dependence of low-frequency internal friction in a quenched and aged aluminum sample (99.999% pure) changes under the effect of weak magnetic field pulses (H≥10⁵ A/m): the general level of internal friction increases. This effect is attributed to the influence of a magnetic field on the structural complex formed by a dislocation and point defects (the role of point defects is played by vacancies).     

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)     

Influence of a weak pulsed magnetic field on grain-boundary relaxation in aluminum

It is discovered that the treatment of technical-grade polycrystalline aluminum in a weak pulsed magnetic field during heating leads to displacement of the grain-boundary maximum of the low-frequency internal friction toward lower temperatures. This phenomenon is associated with a decrease in the degree of interaction of the grain boundaries with impurity atoms. Fiz. Tverd. Tela (St. Petersburg) 41, 1985–1987 (November 1999)     

Magnetoplasticity and magnetic memory in diamagnetic solids

A mechanism for the depinning of dislocations pinned by a stopper is formulated. This mechanism includes the transfer of an electron from a dislocation to the stopper and the appearance of a spin two-electron nanoreactor that has no Coulomb interaction that would hold the dislocation at the stopper in the initial state. The spin dynamics in the nanoreactor is controlled by a magnetic field; therefore, it causes magnetoplasticity and short-term magnetic memory. Another origin of magnetoplasticity is the aggregation of diffusing paramagnetic ions (stoppers) into dimers, trimers, and clusters; this aggregation is also spin-selective and magnetically sensitive. The magnetic-field dependence of the structural evolution of the stoppers provides long-term magnetic memory in diamagnetic solids. Both mechanisms of magnetoplasticity and magnetic memory can coexist and be independent of or dependent on each other.     

Behavior of dislocations in silicon in the presence of mechanical and magnetic perturbations

Various types of dislocation stoppers are identified and their basic parameters are determined. Using dislocation loops as an example, the effect of internal stresses on the motion of linear defects in n-and p-Si in the field of external elastic forces is estimated. It is found that preliminary magnetic treatment of silicon plates activates the dislocation transport. In the absence of external mechanical loads, displacement of dislocation half-loops (30–50 μm) in the nonuniform field of internal stresses in a silicon crystal with a scratch (stress concentrator) is detected experimentally during isothermal annealing for 0.5–3 h at a temperature of 600–700°C. Dislocation transport is described taking into account the intrinsic (lattice) potential barrier of the crystal and two types of stoppers on the basis of magnetosensitive point defects (dopant) and “forest” dislocations. A kinetic model is proposed for describing the magnetostimulated variation of the mobility of linear defects associated with the formation of long-lived complexes with a paramagnetic impurity. It is found experimentally that the velocity of dislocations in n-and p-Si increases by a factor of 2 and 3, respectively, upon treatment of the semiconductor in a magnetic field B=1 T for 5–45 min. The “magnetic memory” effect in silicon containing dislocations is detected and kinetic aspects of the effect under natural conditions of sample storage after the removal of the magnetic field are considered. Partial velocities of dislocations and their delay times at various types of stoppers are calculated from the matching of experiment with theory.     

The physical kinetics of magnetoplasticity of diamagnetic crystals

The kinetic equations describing the rate of magnetically induced release of dislocations entrapped by stoppers were solved. The magnetic field effect on the mobility of dislocations was calculated. Its comparison with experiment gave the ratio between the rate constants for two key processes governing magnetoplasticity, namely, singlet-triplet conversion in a spin nanoreactor and the release of a dislocation from it. The kinetic criterion of the existence of magnetoplasticity as a physical phenomenon was obtained.     

铝-0.5%铜合金中反常振幅效应内耗峰的进一步实验和位错弯结气团模型

用低频扭摆进一步研究了在Al-0.5％Cu合金中观察到反常位错内耗峯的条件。结果指出,对于完全退火的试样来说,需要有适当的冷加工量,但是对于高温淬火试样则不需要冷加工。用位错气团模型定性地解释了过去所观测到的表现反常振幅效应的时效内耗峯和温度内耗峯;同时指出,简单的气团模型在作定量的解释时,遇到了下述的困难:(i)在测量内耗所用的交变应力的作用下,位错线所能够拖着气团移动的距离太短。(ii)为了气团能够被位错拖着移动,组成气团的溶质原子必须具有比通常大很多个数量级的扩散系数。(iii)根据气团模型,从理论上计算出来的使位错拖着气团以临界速度而移动时,所需的临界应力比观测值大几百倍。提出了溶质原子沿着位错弯结而扩散的气团模型,这个改进模型能够初步解决上述困难,并能定性地解释所观测的结果。这个模型所依据的基本假设是,要观测到反常内耗现象,位错线上必须具有一定数目的弯结。要得到这种弯结,可以对于退火试样进行适量的冷加工,或者把试样从高温淬火。带着弯结的位错线能够通过弯结的沿边运动而实现垂直于位错线方向的移动。可以假定,气团只在弯结两端的直位错段处形成,在弯结本身上并不形成气团。在弯结的沿边振动的过程中,聚集在弯结两端的溶质原子可以沿着位错管道进行来回的短程扩散。已知沿着位错管道的扩散具有比在正常晶体点阵中扩散时大得多的扩散系数。     

Evolution of vacancy defects and dislocations in surface layers of iron as a result of pulsed electron beam treatment

Using a micro-beam of ions (PIXE, RBS), a slow positron beam, measurements of positron lifetime, TEM and SEM techniques, formation of vacancy defects and dislocations has been found in a near-surface iron layer as a result of pulsed electron beam treatment. It has been shown that as a result of the HCEB treatment regions of a low local electron density are formed, which seem to be “embryos” for craters. In spite of the crater formation and high dislocation density (exceeding 10¹⁰ cm⁻²) in a near-surface layer, we found a decrease in wear resistance to dry friction and an increase in microhardness.     

Magnetically simulated variation of dislocation mobility in plastically deformed n-silicon

The acoustic emission method is employed for an experimental investigation of the effect of a magnetic field on the mobility of edge dislocations in a plastically deformed n-silicon sample carrying a current. It is found that the preliminary treatment of a dislocated crystal in a constant magnetic field (B<1 T) changes the intensity of its acoustic response depending on the magnetic induction. The observed effect is associated with spin-dependent magnetosensitive reactions of defects occurring in the vicinity of the dislocation core, which facilitate the detachment of the dislocations from the stoppers and, hence, increase the mobility of dislocations and the acoustic response of the dislocation structure.     

Kinetics of accumulation of vacancy complexes in dislocated silicon under 60Co γ-ray irradiation

Abstract

Radiation defect accumulation in ⁶⁰Co γ-ray-irradiated n-type Si single crystals (ρ=150ωcm) with various densities of dislocations (N_D = 1 × 10⁴ to 1 × 10⁷ cm ^?2) introduced at plastic deformation was studied. The temperature dependences of the Hall coefficient were measured. The probabilities of interaction of vacancies with oxygen, phosphorus atoms, and dislocation line elements were determined. It has been established that with the increase of N_D they can increase at the expense of complication of dislocation structure, decrease during formation of impurity atmosphere near dislocations and compensation of deformation fields, and they do not change if complex formation of vacancies with impurities occurs far from dislocations. Kinetics of A- and E-centre accumulation in the crystals containing dislocations with different impurity atmosphere was described.     

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：     

Effect of a pulsed magnetic field on the nonlinear dynamics of vortexlike domain walls in magnetic films

The Landau-Lifshitz equation is numerically solved to study the nonlinear dynamic behavior of domain walls with the 2D vortexlike magnetization distribution in magnetically uniaxial films that have in-plane anisotropy and are exposed to a pulsed magnetic field. It is shown that a pulsed magnetic field H _p may induce transitions between various steady wall motions that differ in magnetization distribution. Solitary rectangular pulses, as well as a regular train of rectangular pulses, may be used to control the period of nonlinear dynamic transformations of the wall internal structure and the related period of variation of the wall velocity.