共查询到19条相似文献,搜索用时 62 毫秒
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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. 相似文献
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颗粒介质是复杂的多体相互作用体系, 其弹性源自内部的力链结构, 弹性能量处在亚稳态, 具有复杂的弛豫行为. 在常规作用下, 颗粒介质往往呈现明显的弹性弛豫. 应力松弛是应变恒定时应力的衰减现象, 弹性弛豫是应力松弛的主要原因. 在前期工作基础上, 从弹性势能面和双颗粒温度热力学角度分析了弹性弛豫的机理, 量化了弹性应力演化不可逆过程; 基于双颗粒温度热力学计算得到了弹性能、颗粒温度和应力的演化, 其中应力松弛的计算结果与实验结果基本一致, 讨论了颗粒温度初值和输运系数的影响. 指出, 开展力链结构及其动力学研究是揭示宏观弹性弛豫机理的关键. 相似文献
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通过计算机编程建立钢奥氏体相中Σ5〈001〉/(210)大角晶界模型,用实空间的递推方法计 算碳、氮及微合金元素在完整晶体及晶界区引起的环境敏感镶嵌能,进而讨论碳、氮及微合 金元素在晶界区的偏聚及交互作用.计算结果表明,轻杂质C,N易偏聚于晶界区,且形成气 团;微合金元素在完整的奥氏体中趋于均匀分布,Ti,V,Nb易占位于晶界三角棱柱的顶部( 压缩区),且其加入量足够大时,它们能够在晶界区形成气团;微合金元素能够偏聚于C,N 掺杂的大角晶界区,当温度下降使得C,N及微合金元素的浓度超过其最大固溶度时,在钢的 奥氏体晶界区将有C,N化合物脱溶,这些化合物既可成为奥氏体再结晶的异质晶核,又可以 阻碍奥氏体晶粒长大,故可起到细化晶粒作用.在微合金元素中Nb的细化效果最好.
关键词:
电子结构
晶界偏聚
超细化 相似文献
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金属高温拉伸试验国际技术标准ISO6892-2-2011认定,拉伸试验的拉伸温度或应变速率的改变会引起拉伸试验测试力学性能结果的不确定性,危及到拉伸试验技术的可靠性. 本文综述了拉伸试验测试断面收缩率或延伸率的不确定性:中温脆性和应变速率脆性的实验现象和特征,简述了多晶金属弹性变形微观理论的基本结果,以此微观理论解释了上述两种测试不确定性的试验现象,阐明了这两种测试不确定性是拉伸试验弹性变形阶段杂质晶界偏聚,脆化了晶界引起的. 为修正金属拉伸试验技术标准,避免断面收缩率测试的不确定性提供了理论基础.
关键词:
拉伸试验
弹性变形
晶界偏聚
断面收缩率 相似文献
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利用大角重位点阵模型建立了Mg合金[0001]对称倾斜晶界模型,应用实空间的连分数方法计算了杂质在晶界的偏聚能,杂质原子间相互作用能和不同体系的费米能级,讨论了杂质在晶界的偏聚行为,杂质间的相互作用与有序化的关系及杂质对镁合金腐蚀性能影响的物理本质. 计算结果表明,杂质原子偏聚于晶界,且主要偏聚于晶界的压缩区;杂质原子间相互排斥,因此在晶界区形成有序相;费米能级与材料的腐蚀电位存在这样的关系:材料的费米能级越高,其腐蚀电位就越低,容易被腐蚀,相反费米能级低,其腐蚀电位就高,不容易腐蚀. 体系中成分不同区域的费米能级差导致电子从费米能级高的区域流向费米能级低的区域,正是费米能级差构成了镁合金电化学腐蚀的电动势.
关键词:
电子理论
晶界偏聚
镁合金
腐蚀机理 相似文献
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内耗理论与实践的奠基者——记葛庭燧教授 总被引:1,自引:0,他引:1
1989年7月在北京召开的第九届国际固体内耗与超声衰减学术会议上,葛庭燧荣获了这一国际科学领域的最高奖--“内耗与超声衰减国际奖”,以表彰他半个世纪以来在这个领域内的理论、实验研究及其他方面的创造性贡献. 相似文献
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Hyun Uk Hong Hi Won Jeong In Soo Kim Baig Gyu Choi Young Soo Yoo Chang Yong Jo 《哲学杂志》2013,93(22):2809-2825
The mechanism of serrated grain boundary formation and its effect on liquation behaviour have been studied in a wrought nickel-based superalloy – Alloy 263. It was newly discovered that grain boundaries are considerably serrated in the absence of γ?′-phase or M23C6 at the grain boundaries. An electron energy-loss spectroscopy study suggests that serration is triggered by the discontinuous segregation of C and Cr atoms at grain boundaries for the purpose of relieving the excessive elastic strain energy. The grain boundaries serrate to have specific segments approaching one {111} low-index plane at a boundary so that the interfacial free energy of the grain boundary can be decreased, which may be responsible for the driving force of the serration. The serrated grain boundaries effectively suppress grain coarsening and are highly resistant to liquation due to their lower wettability resulting from a lower interfacial energy of the grain boundary. 相似文献
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E. Rabkin 《Interface Science》1996,3(3):219-226
The grain boundary diffusion in a binary system which exhibits a grain boundary phase transition is considered in the framework of Fisher's model. The kinetic law of the growth of the grain boundary phase and the distribution of the diffusant near the grain boundary are calculated. The method of determining of the concentration dependence of the grain boundary diffusion coefficient from the experimentally measured penetration profiles of the diffusant along the grain boundaries is suggested. The experimental results on Zn diffusion in Fe(Si) bicrystals, Ni diffusion in Cu bicrystals and grain boundary grooving in Al in the presence of liquid In are discussed in light of the suggested model. 相似文献
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A modified theoretical model is proposed to predict the grain boundary segregation of impurity atoms during high temperature plastic deformation. The model is based on the supersaturated vacancy-impurity complex created by plastic deformation and involves quasi-thermodynamics and kinetics. Model predictions are made for phosphorus grain boundary segregation during plastic deformation in ferrite steel. The results reveal that phosphorus segregates at grain boundaries during plastic deformation. At a given te... 相似文献
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Knowledge of the limits of the principal Harrison kinetics regimes (Types A, B and C) for grain boundary diffusion is very important for the correct analysis of depth profiles in a tracer diffusion experiment. These regimes for self‐diffusion have been extensively studied in the past by making use of the phenomenological lattice Monte Carlo (LMC) method with the result that the limits are now well established. However, the relationship of these self‐diffusion limits to the corresponding ones for solute diffusion in the presence of solute segregation to the grain boundaries remains unclear. In the present study, the influence of solute segregation on the limits was investigated with the LMC method for the well‐known parallel grain boundary slab model by showing the equivalence of two diffusion models. It is shown which diffusion parameters are useful for identifying the limits of the Harrison kinetics regimes for solute grain boundary diffusion. It is also shown how the measured segregation factor from the diffusion experiment in the Harrison Type‐B kinetics regime may differ from the global segregation factor. 相似文献
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Segregation of alloying atoms at a tilt symmetric grain boundary in tungsten and their strengthening and embrittling effects 下载免费PDF全文
We investigate the segregation behavior of alloying atoms (Sr, Th, In, Cd, Ag, Sc, Au, Zn, Cu, Mn, Cr, and Ti) near Z3 ( 111 ) [1]-0] tilt symmetric grain boundary (GB) in tungsten and their effects on the intergranular embrittlement by performing first-principles calculations. The calculated segregation energies suggest that Ag, Au, Cd, In, Sc, Sr, Th, and Ti prefer to occupy the site in the mirror plane of the GB, while Cu, Cr, Mn, and Zn intend to locate at the first layer nearby the GB core. The calculated strengthening energies predict Sr, Th, In, Cd, Ag, Sc, Au, Ti, and Zn act as embrittlers while Cu, Cr, and Mn act as cohesion enhancers. The correlation of the alloying atom's metal radius with strengthening energy is strong enough to predict the strengthening and embrittling behavior of alloying atoms; that is, the alloying atom with larger metal radius than W acts as an embrittler and the one with smaller metal radius acts as a cohesion enhancer. 相似文献
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AbstractThe grain boundaries (GBs) present in polycrystalline materials are important with respect to materials behaviour and properties. During the transient stage of oxidation, the higher GB diffusivity results in heterogeneous oxidation structures in the form of oxide ridges that emerge along the alloy GBs. In an attempt to delve into the more fundamental aspects of the GBs, such as GB energy, the size of the oxide ridges was quantitatively measured by atomic force microscopy on the post oxidation surface of a Fe-22 wt % Cr alloy after an oxidation exposure at 800 °C in dry air. The GB diffusivity was calculated utilising the ridge size data and the relationship between the GB diffusivity and the GB characteristics was determined. Furthermore, the GB energy was calculated from the GB diffusivity data, also to make comparison with the data available in the literature. The absolute value of the calculated GB energy was quite close to the values reported in the literature. However, compared to the extremely low temperature (0 K) data-set from the literature, the data-set obtained from this study showed much less spread. The smaller variation range may be attributed to the higher temperature condition (1073 K) in this study. 相似文献
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Stefan Bringuier Venkateswara Rao Manga Keith Runge Pierre Deymier Krishna Muralidharan 《哲学杂志》2015,95(36):4118-4129
The mechanical response of symmetric tilt grain boundaries (GBs) in silicon bicrystals under shear loading are characterized using molecular dynamics simulations. It is seen that under shear, high-angle GBs namely Σ5 and Σ13 having a rotation axis [0 0 1] demonstrate coupled GB motion, such that the displacement of grains parallel to the GB interface is accompanied by normal GB motion. An atomic-scale characterization revealed that concerted rotations of silicon tetrahedra within the GB are the primary mechanisms leading to the coupled GB motion. Interestingly, so far, this phenomenon has only been examined in detail for metallic systems. A distinguishing feature of the coupled GB motion observed for the silicon symmetric tilt bicrystals as compared to metallic bicrystals is the fact that in the absence of shear, spontaneous coupled motion is not observed at high temperatures. 相似文献