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《中国有色金属学报》2015,(8)
采用密度泛函理论(DFT)中的广义梯度近似(GGA)对MomSn(m+n≤8)团簇进行结构优化,通过计算其二阶能量差分Δ2Em、分裂能D(m)、平均结合能Eb、最高占据轨道(HOMO)、最低空轨道(LUMO)和HOMO-LUMO能隙HLG,以表征与分析团簇总原子数对MomSn团簇基态结构稳定性的影响。计算结果表明:随着总原子数(m+n)的增大,MomSn团簇的基态结构由较为松散的平面结构向紧凑型的空间结构转变,其基态几何构型与Sn团簇以及Mom团簇的基态几何构型密切相关;MomSn团簇结构稳定性随团簇原子总数(m+n)的增加而增大,MomSn团簇的平均结合能比Sn团簇和Mom团簇的平均结合能要大;Mo Sn团簇、Mo2Sn团簇、Mo3Sn团簇的幻数(n)分别为5、4、3;在MomSn团簇中,电荷均是由Mo原子向S原子转移的,并以共价键和离子键共存。 相似文献
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基于Three Dimensional Atom Probe(3DAP)以及First-Principles对Al-Si-Cu-Mg合金中团簇及后续沉淀的演变过程进行了研究。3DAP试验表明,Al-1.0Si-1.5Cu-0.5Mg合金时效0.25h后基体中主要存在点状的Si-Si团簇、Si-Mg团簇、Si-Mg-Cu团簇,与第一性原理计算所表明的以上各结构中溶质原子间结合较强的结果相符,同时由于大量Si原子的扩散聚集,导致Si-Cu团簇结构出现;时效0.25~2h后基体中Si、Mg、Cu原子继续聚集,点状的Si-Si、Si-Cu、Si-Mg团簇长大并向针状的Si-Mg-Cu团簇演变;时效2~4h后,Si、Mg、Cu原子继续聚集,促进针状Si-Mg-Cu结构长大的同时,部分大尺寸的Si-Mg-Cu结构逐渐向板条状的Q′相转变,同时富Cu结构出现。 相似文献
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钢中细小、弥散分布的钛氧化物可以诱导晶内铁素体的形成,提高钢的力学性能。通过分子动力学方法模拟研究了Ti-O团簇长大演化成为钛氧化物的过程,并探究了钢液环境与空位对Ti-O团簇形貌的影响。结果发现:在真空中以球状结构稳定存在的Ti-O团簇在钢液中呈蠕虫状或树枝状。通过比较低能Fe原子在Ti-O团簇周围和钢液中的分布,发现在团簇内O原子周围0.25~0.30 nm范围内Fe原子出现聚集,说明钢液中Fe原子对Ti-O团簇中的O原子产生作用,使Ti-O团簇形貌发生变化。空位易在距离Ti-O团簇表面0.45 nm范围内聚集,空位扩散加速了Ti-O团簇的碰撞长大。 相似文献
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研究多个典型非晶形成体系合金相结构中的团簇规律,指出在合金相结构中团簇之间以不同方式共享原子的事实。共享后的有效团簇到合金相的连接方式有两种,一种是共享后的团簇成分就是相成分,无须连接原子,另一种是共享后的团簇加上连接原子才能构成空间相结构(这类相称之为团簇相)。这种方法使得对合金相的结构有了一个全新的理解。在典型的非晶形成体系Zr-Al-Ni中,团簇相有3个:AlNiZr-Fe2P结构,Al2NiZr6-InMg2结构和Al5Ni3Zr2-Mn23Th6结构。通过此项工作还提出了基于合金相结构来确定与非晶形成相关的团簇的方法,即与非晶相关的团簇一般为团簇相里出来的孤立团簇,这一结论在Zr-Al-Ni体系中得到了很好的验证。 相似文献
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亚共晶Al-Si合金共晶团的形核与生长 总被引:1,自引:0,他引:1
采用光学显微镜、扫描电镜及电子背散射衍射技术研究亚共晶Al-Si合金共晶团的形核与生长。通过揭示共晶团和结晶位向的分析发现:在同一个共晶团中Si相和Al相都不是单晶体,而是由不同位向的小"晶粒"构成的。提出不能依据共晶团中Al相与周围初生枝晶Al相的位向关系来确定共晶的形核模式的建议。然而,初生枝晶铝相的演化显著影响随后的共晶形核与生长。涉及的杂质元素使共晶Si的形貌由粗大的片状转变成细小的纤维状的变质行为,可能与共晶的形核无关。 相似文献
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采用密度泛函理论框架下的广义梯度近似(DFT/GGA),对V13团簇及V12M掺杂团簇(M=Sc,Ti,Cr,Mn,Fe,Co,Ni,Y,Zr,Nb,Mo,Tc,Ru)的电子结构和磁性进行研究.通过对团簇的基态几何构型优化计算得到了团簇束缚能、电子结构以及磁矩的大小,系统地分析了V13和V12M团簇磁矩的形成机理以及电子结构与磁性的变化关系.发现掺杂团簇V12Fe和V12Ru为具有大束缚能和大能隙间隔的闭壳电子结构,V12Y团簇具有11μB的大磁矩,而其它掺杂团簇则表现为弱磁性. 相似文献
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合金相的“团簇+连接原子”模型与成分设计 总被引:1,自引:0,他引:1
以最近邻配位多面体为基元描述复杂合金相的结构特征,总结出合金相的常见团簇类型,并建立了合金相的团簇+连接原子模型。以此为基础解析准晶和非晶合金为代表的团簇合金的结构与团簇成分式特征,提出复杂合金相成分设计的团簇式方法,并以块体非晶合金和稳定固溶体合金为例说明多组元合金相团簇成分式的建立与运用过程以及团簇基元及连接原子种类与数目的确定原则。前期研究工作表明,基于团簇+连接原子模型的团簇成分式方法为多元复杂合金相定量设计提供了新的有效途径。 相似文献
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团簇离子束是带电的团簇,可以在电场、磁场作用下加速、传输或偏转,形成几个eV到几个MeV能量的离子束。文中阐述了团簇离子束的基本概念、产生方法和主要应用。大尺寸气体团簇和硼基团簇必须用高压气体超声绝热膨胀方法产生,然后通过电子碰撞电离形成团簇正离子。硼团簇用于超浅结制备,实现了结深为10~20nm的超浅注入;包含数千原子的大团簇则被用于半导体的表面平化,获得了粗糙度在0.7nm以下的平滑表面。用铯溅射离子源可以产生几个到几十个原子的负离子小团簇,包括B、C、F、Si及其分子团簇(SiB、GeB)。其中,硼基分子团簇离子束已用于对半导体进行瞬态增强扩散掺杂,与半导体表面的离子注入非晶化工艺相结合,实现了接近纳米量级的超浅注入。碳系团簇最近被用于超薄材料制备,获得了单层和双层石墨烯,并发现团簇离子束引起的非线性辐照损伤对石墨烯的形成具有重要影响。结果表明:团簇离子技术在超大集成电路和新型超薄纳米材料制备等领域具有广泛的应用前景。 相似文献
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V. O. Esin A. S. Krivonosova I. Zh. Sattybaev T. G. Fedorova 《The Physics of Metals and Metallography》2007,103(3):317-323
The distribution of dislocation density has been investigated experimentally in aluminum single crystals with various concentrations of copper impurity (~0.0002, 0.005, and 0.05 wt %) that were obtained upon the crystallization of the melt under the action of a pressure and the gravitational-field component directed along the surface of the crystallization front. It has been found that a strong nonuniformity in the dislocation distribution arises in cross sections of the crystals in the direction of the field and this nonuniformity increases with increasing gravitational-field component and decreasing in the impurity concentration and rate of crystallization of the melt. It has been found that the degree of nonuniformity of the dislocation distribution in the crystals substantially depends on the magnitude of pressure at which the crystallization of the melt is realized and reaches a maximum at a certain pressure that is “optimum” for given conditions of the process of phase transformation. 相似文献
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采用四电极电阻法研究Al85Ni5Y8Co2合金熔体电阻率,并结合X射线衍射仪(XRD)和差示扫描量热仪(DSC)探索熔体结构变化对Al85Ni5Y8Co2非晶晶化行为的影响。结果表明:Al85Ni5Y8Co2合金在1135~1357 K温度区间内发生熔体结构变化,而熔体结构变化导致Al85Ni5Y8Co2非晶晶化行为存在差异;在熔体温度为1673 K下制备的非晶薄带第一晶化较1323 K和1523 K的明显提前,对激活能的计算证实其初晶化更容易析出FCC-Al,且更难析出Al2Y3、Al13Co4、Al9Co2和AlNi等脆性金属间化合物;通过XRD的测试发现高的熔体温度可能会导致熔体中原子团簇的破坏,从而引起非晶晶化行为的改变。 相似文献
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磁控溅射铬镀层的微观组织结构研究 总被引:1,自引:1,他引:0
采用磁控溅射技术制备了铬镀层,利用X射线衍射仪研究了铬镀层的物相和择优生长取向,并结合扫描电子显微镜和透射电子显微镜观察、分析了铬镀层的微观组织结构.研究结果表明:磁控溅射铬镀层呈多晶态结构,以Cr(110)晶面为择优生长面;铬镀层截面呈柱状生长特性,在沉积的最初阶段即形核晶化,随着沉积时间的延长,晶化程度逐渐提高. 相似文献
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Tsivirko É. I. Zhemanyuk P. D. Klochikhin V. V. Naumik V. V. Lunev V. V. 《Metal Science and Heat Treatment》2001,43(9-10):382-386
The effect of high-temperature melt treatment (HTMT), regimes of crystallization, and heat treatment on the structure and properties of castings from high-temperature nickel alloys ZhS3DK-VI, ZhS26-VI, and ZhS32-VI is investigated. It is shown that an optimum HTMT process noticeably decreases the nitrogen content in alloy ZhS3DK-VI and improves its structure and properties. Directed crystallization of alloys ZhS26-VI and ZhS32-VI is more effective than volume crystallization for diminution of the structural components, reduction of dendritic segregation, and elevation of the crack resistance of the metal. Heat treatment of alloy ZhS32-VI at 1270°C instead of 1210°C provides a favorable microstructure and a higher strength level in the material. 相似文献
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DSC法研究Ni镀层熔体的过冷及结晶度 总被引:2,自引:0,他引:2
将DSC技术与助熔剂(BaCl2)处理技术相结合,在不同温度下原位测试了Ni镀层熔体的过冷度。在1849K温度下(冷却速率为20K/min)获得了Ni镀层熔体的最大过冷度为411K。冷却速率在10K/min~50K/min范围内,冷却速率越大,过冷度越大。当冷却速率一定的情况下,过冷度随熔体处理温度的提高而增大,并逐步趋向于恒定。分析了Ni镀层熔体的结晶率与温度、冷却速率和时间的关系。 相似文献
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A melt maintained for hours in a press pour unit allowed the following changes over time from spheroidal graphite to compacted graphite iron by casting thermal cups at regular time intervals.This provided extensive experimental information for checking the possibility of simulating solidification of compacted graphite irons by means of a microstructure modelling approach.During solidification,compacted graphite develops very much as lamellar graphite but with much less branching.On this basis,a simulation of the thermal analysis records was developed which considers solidification proceeding in a pseudo binary Fe-C system.The simulated curves were compared with the experimental ones obtained from three representative alloys that cover the whole microstructure change during the holding of the melt.The most relevant result is that the parameter describing branching capability of graphite is the most important for reproducing the minimum eutectic temperature and the recalescence which are so characteristic of the solidification of compacted graphite cast irons. 相似文献
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亚共晶Al—Si合金熔体处理的研究进展 总被引:22,自引:4,他引:22
评述了近年来在亚共晶Al-Si合金的净化、变质和晶粒细化等熔体处理领域所取得的进展,指出将喷射熔剂法用于整个熔体处理过程是今后的发展趋势。 相似文献
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Joel J. Schubbe 《Journal of Materials Engineering and Performance》2011,20(1):147-154
A study has been accomplished to characterize the fatigue crack growth rates and mechanisms in thick plate (16.51 cm) commercial
grade 7050-T7451 aluminum plate in the L-S orientation. Examination of the effects of potential property gradients in the
plate material was accomplished through hardness measurements along the short transverse direction and with compact tension
tests. Tests exhibited a distinct trend of reduced center plane hardness in the plates. Compact tension specimens and the
compliance method were used to determine crack growth rates for specimens machined from the t/4 and t/2 planar locations and
oriented for L-S crack growth. Crack growth rate data (long crack) from the tests highlighted significant growth rate differences
between the t/4 and t/2 locations. No significant effect of R-ratio was observed in the 0.05-0.3 range tested. Additionally, crack front splitting was noted in all specimens to differing
degrees with data showing significant retardation of growth rate curves for the L-S orientation above 13 MPa √m in the center
plane, and 10 MPa √m at quarter plane, where branching and splitting parallel to the load axis are dominant growth mechanisms. 相似文献
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Lunyong Zhang Hongbo Zuo Dawei Xing Jiecai Han Jianfei Sun 《Metals and Materials International》2010,16(5):725-730
A 1-D crystallization process has been analyzed for thermal diffusion by solving the Fourier equation. The expressions of
thermal fields indicate that the temperature decreases as the crystal grows and the temperature decreases in the solid phase
as the crystal growth rate decreases. The trend of temperature variation is the opposite in the liquid phase. Meanwhile the
temperature gradient decays along the crystal growth direction in both the solid and liquid phases. An obvious temperature
layer gradually appears as the crystal growth rate increases when the crystal grows in an undercooled melt. According to these
results, the following guidelines are suggested for the quantitative process design of the 1-D crystallization at a constant
crystal growth rate: (1) the heater temperature must be decreased as the crystal grows along a route established using a formula,
(2) the linear simplification of temperature distribution is applicable to the process design of crystallization only below
a high growth rate limit, and (3) in order to keep the crystal growing in a non-undercooled melt, its growth rate cannot exceed
a maximum. 相似文献