共查询到18条相似文献,搜索用时 250 毫秒
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本文试图从位错理论出发来探索晶体脆性断裂的统计理论。脆性断裂过程,实质上是微裂缝在极小的范性形变过程中形成长大和传播的随机过程。本文导出了描述这种随机过程的微分方程,利用微裂缝形成长大的位错机理,解出了微裂缝大小的统计分布函数。文中给出了范性形变、加工硬化和活动位错源数目与微裂缝数目和大小之间的函数关系。过去研究脆性断裂时,范性变形只是含糊地包括在有效表面能之内,而加工硬化和活动位错源数目则一向被略去。从微裂缝大小的统计分布函数和微裂缝的传播条件,导出了强度的统计分布函数,从而求得了脆性断裂判别式、脆性断裂强度及脆性-范性转变温度。 相似文献
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本文从反应扩散方程出发,研究在辐照条件下,微洞和位错(无应力场)周围点缺陷的分布情况。对含有点缺陷复合项的定态的反应扩散方程,给出了一种近似求解的方法并分别得到了微洞和位错吸收点缺陷的汇强度。从所得结果与前人略去复合项的结果比较可知,微洞较大时,复合项对汇强度的影响变得重要;对于位错,当点缺陷产生率较大时,考虑了复合项后所得的汇强度可达前人结果的1.5倍以上。 相似文献
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本文从反应扩散方程出发,研究在辐照条件下,微洞和位错(无应力场)周围点缺陷的分布情况。对含有点缺陷复合项的定态的反应扩散方程,给出了一种近似求解的方法并分别得到了微洞和位错吸收点缺陷的汇强度。从所得结果与前人略去复合项的结果比较可知,微洞较大时,复合项对汇强度的影响变得重要;对于位错,当点缺陷产生率较大时,考虑了复合项后所得的汇强度可达前人结果的1.5倍以上。
关键词: 相似文献
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《物理学报》2020,(11)
在辐照环境下,载能粒子与材料相互作用导致材料中原子移位,造成辐照损伤.其中,由辐照形成的过饱和自间隙原子团簇形成的间隙型位错环,是体心立方Fe为基的材料中常见的辐照缺陷之一,其与材料中其他缺陷之间相互作用,是导致辐照硬化、脆化、肿胀及蠕变等辐照损伤的原因之一.除此相互作用外,在材料表面或内部沿晶界、沉积相、惰性气体形成的气泡所导致的微裂纹,是诱发辐照促进应力腐蚀开裂的重要原因.因此,理解辐照条件下间隙型位错环与微裂纹之间的相互作用,是理解辐照促进应力腐蚀开裂微观机制的重要一步.在本研究中,利用分子动力学方法,模拟了原子尺度微裂纹与间隙型位错环之间的相互作用,研究了位错环与微裂纹之间的距离、相对位置及位错环尺寸对二者相互作用的影响,揭示了位错环对微裂纹是否沿滑移面扩展的影响,发现当二者的相互作用起主导作用时(如在临界水平或垂直距离之内),形成的以100为主或高密度的1/2111位错网络可以抑制微裂纹沿滑移面的扩展.当位错环尺寸发生变化时,只有当位错环位错核与微裂纹尖端相互作用时,才能抑制微裂纹沿滑移面的扩展.这些结果为进一步理解辐照应力开裂提供了新的参考. 相似文献
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通过AB腐蚀(由Abrahams和Buiocchi发明的腐蚀方法,简称AB腐蚀)、KOH腐蚀,经金相显微镜观察、透射电子显微镜能谱分析、电子探针x射线微区分析,对液封直拉法生长的非掺 半绝缘砷化镓单晶中碳的微区分布进行了分析研究.实验结果表明,碳的微区分布受单晶中 高密度位错网络结构的影响.高密度位错区,位错形成较小的胞状结构,且胞内不存在孤立 位错,碳在单个胞内呈U型分布;较低密度位错区,胞状结构直径较大,且胞内存在孤立位 错,碳在单个胞内呈W型分布.
关键词:
半绝缘砷化镓
胞状位错
碳受主 相似文献
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Reactions between superdislocations involved in deformation in the basal, prismatic, and type-I and II pyramidal planes in single-crystal Ti3Al are considered. The types of dislocation interactions are established that result in the formation dislocation barriers (microcrack nuclei). The force and energy conditions for microcracks to arise are found. The interaction between a and 2c + a superdislocations results in microcracks with the plane of opening lying in basal and pyramidal planes; the interaction of 2c + a superdislocations in different pyramidal planes results in the formation of microcracks in prismatic and pyramidal planes; and the interaction of a superdislocations in basal and/or pyramidal planes does not cause the formation of dislocation barriers. The types of microcracks are classified in terms of the orientation of deformation axes of single crystals, and the regions of the stereographic triangle are determined characterized by a preferential type of crack opening. 相似文献
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The dynamics of nucleation of microcracks in the region of a developing macroscopic crack has been studied using scanning
electron microscopy during in situ experiment and the acoustic emission method. An explosive-like nucleation of microcracks
and the influence of dissipative properties of a material on the size and the rate of redistribution of local stresses of
the microcracks have been established. Each of nucleations of microscopic and mesoscopic defects is considered as an act of
local testing of the dissipative ability of the system, and the interaction between microcracks is determined by relaxation
processes when the ability is sufficient. With deteriorating dissipative properties (with increasing residence time under
loading, deformation rate, etc.), an elastic linear interaction becomes possible, and the macroscopic fracture occurs. In
the microcrack dynamics, a specific ductile-brittle transition is determined by a time deterioration of the dissipative properties
of the material under the action of a mechanical load. Generally, as a large latent energy is stored during deformation, a
macroscopic fracture can be caused by any little discrete structural transformation. 相似文献
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L. I. Yakovenkova L. E. Kar’kina O. A. Elkina 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(5):607-609
The formation of microcracks upon dislocation interactions was studied by means of TEM analysis. The types of microcracks
were classified depending on the orientation of deformation axes in single crystals. The Griffith surface energy was simulated,
and the energy of unstable stacking faults was calculated by the molecular dynamics method using the N-particle EAM potentials of the interatomic interaction for Ti3Al. The Rice—Thompson model was used to study the relationship between the tendency toward cleavage and the plastic relaxation
of stresses near a crack tip by the emission of dislocations in Ti3Al single crystals. 相似文献
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E. Bugiel M. Lewerenz H.J. Osten 《Physica E: Low-dimensional Systems and Nanostructures》2007,37(1-2):250
We show a new way to fabricate well-defined individual dislocations in SiGe. We started with a fully pseudomorphic but metastable SiGe layer grown on Si(0 0 1) by molecular beam epitaxy. Next, elongated (1 mm) mesa stripes with various widths (0.5–3 μm) were fabricated by a combination of isotropic and anisotropic etching. For smaller stripes, elastic relaxation of the strained SiGe layer can occur, transforming the originally biaxial strained layer into uniaxial strained subsystems. Subsequent strain relaxation caused by high temperature treatments leads to the formation of individual dislocation along the mesa stripes. The number of parallel dislocation can be adjusted by the original strain (Si:Ge ratio and layer thickness) and the mesa widths. We were able to fabricate structures with exactly one dislocation. Finally, contact pads were added to the stripes enabling the electrical characterization of individual dislocation. 相似文献
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Dislocation motion in the real lattice of alloys is highly complex. In a certain temperature range the dynamic strain ageing phenomena have been reported. In this paper the influence of mobile solute atoms (as obstacles) on the motion of dislocation is analysed. Both processes are assumed to be thermally activated. A new model based on this assumption is proposed. The dislocation velocity and the friction stress (due to solute-dislocation interactions) are calculated. A change in the friction stress caused by solute mobility is discussed. 相似文献
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V. A. Makara L. P. Steblenko I. V. Plyushchai A. N. Kurylyuk D. V. Kalinichenko A. N. Krit S. N. Naumenko 《Physics of the Solid State》2014,56(8):1582-1589
The possibility of magnetic ordering at dangling bonds in dislocation cores has been investigated theoretically. It has been experimentally shown that magnetic ordering in dislocations affects the spin-dependent effects occurring in dislocation crystals of silicon. It has been found that preliminary magnetic treatment of silicon crystals in a weak magnetic field leads to the suppression of the electroplastic effect induced in silicon crystals excited by an electric current. It has been assumed that a change in the microplasticity under the combined action of a magnetic field and an electric current is caused by a weakening of spin-dependent recombination at dislocation dangling bonds. 相似文献
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Dr. Heino Freese 《Zeitschrift für Physik B Condensed Matter》1971,13(2):149-155
Within the Heisenberg model the scattering of spin waves by a dislocation can be calculated in the low energy limit, taking into account the structure of a simple cubic lattice. The differential cross section for the scattering by a screw dislocation is shown to have the same form as for the scattering by a step dislocation, if thes-wave-scattering caused by local disturbances is neglected. 相似文献
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In this work, the EDIP potential is employed for representing silicon and the shuffle-set 60° perfect dislocation motion is investigated by reaction pathway analysis. There are three possible shuffle-set 60° perfect dislocation core structures named as S1, S2 and S3. The activation energy barriers of the kink migration and nucleation in S1and S2 types are calculated by CI-NEB method. The simulation results show that the critical resolved shear strain of the shuffle-set dislocation in S1 type is around 5%, and the S1 type is the dominate one in the shear strain region of 0 to 5%. During the shear strain from 5to 11.81%, the dislocation moves as the S1 core kink nucleation and migration, meanwhile the S1 dislocation core is in process of transforming into S2. More interestingly, both S1 and S2 dislocation core structures is observed along the dislocation line in this shear strain regime, which could response to the missing observation of long segment dislocation line in the experiment. 相似文献