共查询到18条相似文献,搜索用时 93 毫秒
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采用晶体相场模型模拟获得了平均晶粒尺寸从11.61–31.32 nm的纳米晶组织, 研究了单向拉伸过程纳米晶组织的强化规律的微观变形机理. 模拟结果表明: 晶粒转动、晶界迁移等晶间变形行为是纳米晶材料的主要微观变形方式, 纳米晶尺寸减小, 有利于晶粒转动, 使屈服强度降低, 显示出反霍尔-佩奇效应.当纳米晶较小时, 变形量超过屈服点达到4%, 位错运动开启, 其对变形的直接贡献有限, 主要通过改变晶界结构而影响变形行为, 位错运动破坏三叉晶界, 引发晶界弯曲, 促进晶界迁移. 随纳米晶增大, 晶粒转动困难, 出现晶界锯齿化并发射位错的现象.
关键词:
晶体相场
纳米晶
反霍尔-佩奇效应
微观变形 相似文献
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推导出了单相纳米晶合金的晶界过剩体积与晶粒尺寸之间的定量关系, 建立了纳米晶合金的晶界热力学性质随温度和晶粒尺寸发生变化的确定性函数. 针对SmCo7纳米晶合金, 通过纳米晶界热力学函数计算和分析, 研究了单相纳米晶合金的晶粒组织热稳定性. 研究表明, 当纳米晶合金的晶粒尺寸小于对应于体系中晶界自由能最大值的临界晶粒尺寸时, 纳米晶组织处于相对稳定的热力学状态; 当纳米晶粒尺寸达到和超过临界尺寸时, 纳米晶组织将发生热力学失稳, 导致不连续的快速晶粒长大. 利用纳米晶合金热力学理论与元胞自动机算法相耦合的模型对SmCo7纳米晶合金在升温过程中的晶粒长大行为进行了计算机模拟, 模拟结果与纳米晶合金热力学模型的计算预测结果一致, 由此证实了关于纳米晶合金晶粒组织热稳定性的研究结论.
关键词:
纳米晶合金热力学
7纳米晶合金')" href="#">SmCo7纳米晶合金
热稳定性
计算机模拟 相似文献
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采用自行开发计算机软件,建立了铝晶粒大角度重位点阵晶界模型及碳纳米管与铝金属的界面结构,利用递归法计算了纳米碳管增强铝基复合材料的电子结构参数(铝晶界、铝与纳米管界面及纳米管的结构能,体系费米能级等). 计算结果表明:Σ为5的晶界结构能最低,比较稳定;纳米碳管在铝晶粒的晶界处与铝形成的界面结构能较低,复合材料中纳米碳管主要分布在铝晶粒的晶界处;铝提高纳米碳管的结构能,降低纳米碳管的稳定性,增强碳管的物理化学活性,且管口处的碳原子稳定性较差,易与周围环境中的原子结合生成稳定结构.
关键词:
电子结构
晶界
铝复合材料
纳米管 相似文献
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纳米尺度金属Ag以其独特的导电和导热性,广泛应用于微电子、光电子学、催化等领域,特别是在纳米微电极和纳米器件方面的应用.本文采用分子动力学方法模拟了不同晶粒尺寸下多晶银纳米线的拉伸变形行为,详细分析了晶粒尺寸对多晶银纳米线弹性模量、屈服强度、塑性变形机理的影响.发现当晶粒尺寸小于13.49 nm时,多晶Ag纳米线呈现软化现象,出现反Hall-Petch关系,此时的塑性变形机理主要以晶界滑移、晶粒转动为主,变形后期形成五重孪晶;当晶粒尺寸大于13.49 nm时,塑性变形以位错滑移为主,变形后期产生大量的孪晶组织. 相似文献
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This paper
reports a molecular dynamics simulation for atomic structure of copper nanocrystals,in
which the grain size and lattice distortion were computed by X-ray diffraction
simulation,and the distribution of energy and elastic modulus was calculated.The results
show that the lattice distortion was stored not only at grain boundaries but also in the
grain.The increase of atomic radius leads to the reduction of the elastic modulus of the
nanocrystals. 相似文献
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Pressure-induced structural transformations in spherical and faceted gallium arsenide nanocrystals of various shapes and sizes are investigated with a parallel molecular-dynamics approach. The results show that the pressure for zinc blende to rocksalt structural transformation depends on the nanocrystal size, and all nanocrystals undergo nonuniform deformation during the transformation. Spherical nanocrystals above a critical diameter >/=44 A transform with grain boundaries. Faceted nanocrystals of comparable size have grain boundaries in 60% of the cases, whereas the other 40% are free of grain boundaries. The structure of transformed nanocrystals shows that domain orientation and strain relative to the initial zinc blende lattice are not equivalent. These observations may have implications in interpreting the experimental x-ray line shapes from transformed nanocrystals. 相似文献
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利用不含有机相的简单水热法制备了Co^2+∶ZnS纳米晶,纳米晶具有立方闪锌矿结构,平均晶粒尺寸约为8.3 nm,在808 nm激光泵浦下具有2~5μm波段的中红外荧光发射,中心波长位于3400 nm和4700 nm,分别对应Co^2+离子的4T2(F)→4 A 1(F)和4T1(F)→4T2(F)的能级跃迁.进一步将制备的纳米晶在还原气氛下进行800℃热处理,获得立方闪锌矿和纤锌矿混合晶型的纳米晶,平均晶粒尺寸增大到22.5 nm左右,热处理后的纳米晶表面羟基含量更低,中红外荧光发射强度显著提高.该Co^2+∶ZnS纳米晶的制备方法简单、在制备过程中不引入有机相等荧光淬灭中心,同时证明通过后热处理过程可以进一步减少表面缺陷及羟基含量,使荧光强度得到大幅提升. 相似文献
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The crystal structure and electric properties of BaTiO3 nanocrystals are studied by in situ high-pressure synchrotron radiation x-ray powder diffraction. The phase transition takes place not only in the samples of BaTiO3 nanocrystals that are tetragonal phase with grain sizes more than 100nm, but also in the samples of BaTiO3 nanocrystals that are cubic phase with grain sizes less than 100nm. The pressures of phase transition are found to increase with decrease of the grain size from about 4 to 10GPa for crystallites ranging from 200 to 10nm in radius. The bulk moduli are calculated according to Birch-Murnaghan state equation before and after the phase transition. 相似文献
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Atomic simulations of the growth of polycrystalline Ni demonstrate that deposited atoms incorporate into the film at boundaries, resulting in compressive stress generation. Incorporated atoms can also leave the boundaries and thus relieve compressive stress. This leads to a complex interplay between growth stress, adatom incorporation, and surface structure. A simple, theoretical model that accounts for grain size effects is proposed and is in good agreement with simulation results. 相似文献
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以醋酸钡和钛酸四丁酯为原料,采用溶胶-凝胶法合成了纳米BaTiO3粉体;运用差示/热重、X射线衍射及透射电镜对前驱体凝胶和产物进行了表征,并根据XRD结果,研究了纳米BaTiO3的晶格常数、晶格畸变度和晶粒尺寸随焙烧温度及时间的变化。结果表明,焙烧温度与时间对纳米BaTiO3晶格常数的影响不明显;随焙烧温度或时间的延长,纳米BaTiO3的晶格畸变度减小,晶粒尺寸增大,但晶格畸变度和晶粒尺寸更敏感于焙烧温度. 基于扩散控制机理的传统模型探讨了焙烧过程纳米BaTiO3晶粒生长动力学,得出其晶粒生长指数为7,晶粒生长活化能为75.49 kJ/mol. 将基于扩散与反应共同控制机理的新型等温模型应用于本研究中,结果表明,新型等温模型更能真实地反映纳米BaTiO3焙烧过程中的晶粒生长行为,说明纳米BaTiO3晶粒生长过程同时受溶质扩散和表面反应控制,其藕合晶粒生长活化能为27.23 kJ/mol. 相似文献
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I. N. Kar’kin L. E. Kar’kina P. A. Korzhavyi Yu. N. Gornostyrev 《Physics of the Solid State》2017,59(1):106-113
The kinetics of decomposition of a polycrystalline Fe–Cu alloy and the formation of precipitates at the grain boundaries of the material have been investigated theoretically using the atomistic simulation on different time scales by (i) the Monte Carlo method implementing the diffusion redistribution of Cu atoms and (ii) the molecular dynamics method providing the atomic relaxation of the crystal lattice. It has been shown that, for a small grain size (D ~ 10 nm), the decomposition in the bulk of the grain is suppressed, whereas the copper-enriched precipitates coherently bound to the matrix are predominantly formed at the grain boundaries of the material. The size and composition of the precipitates depend significantly on the type of grain boundaries: small precipitates (1.2–1.4 nm) have the average composition of Fe–40 at % Cu and arise in the vicinity of low-angle grain boundaries, while larger precipitates that have sizes of up to 4 nm and the average composition of Fe–60 at % Cu are formed near grain boundaries of the general type and triple junctions. 相似文献
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O. B. Perevalova E. V. Konovalova Yu. R. Kolobov A. I. Korshunov 《Bulletin of the Russian Academy of Sciences: Physics》2018,82(7):773-777
The grain structure of M1 copper subjected to equal-channel angular pressing (ECAP) and subsequent annealing at 593K for 1 h is studied by means of transmission electron microscopy and scanning electron microscopy with the diffraction of backscattered electrons. An increase in grain size and the formation of special boundaries (Σ3 twins both coherent and incoherent) are observed, along with the migration of high-energy Σ3 twins and common grain boundaries, the splitting of Σ9 special boundaries into Σ3 twins, and the splitting of common grain boundaries into Σ9 and Σ3 special boundaries. The local transformation of common grain boundaries into special boundaries also occurs. Particles of the Cu2O phase are present on the migrating Σ3 twins and common grain boundaries. 相似文献