共查询到20条相似文献,搜索用时 187 毫秒
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利用电磁悬浮无容器处理技术实现了液态五元Zr57Cu20Al10Ni8Ti5合金的深过冷与快速凝固,同时通过分子动力学模拟计算揭示了非晶形成的微观机制.实验发现,凝固组织具有明显的核-壳结构特征,核区为非晶相,壳区主要由ZrCu, Zr2Cu和Zr8Cu5晶体相组成.非晶体积分数随合金过冷度的升高逐渐增大,当达到实验最大过冷度300 K (0.26TL)时,非晶体积分数增至81.3%.由此导出完全非晶凝固所需临界过冷度为334 K. TEM分析显示,过冷度增大并接近临界过冷度时,合金凝固组织中晶体相主要为Zr8Cu5相,而ZrCu和Zr2Cu相的生长被抑制.在达到临界过冷度后,过冷液相的凝固路径由Zr8Cu5结晶生长转变为非晶凝固.此外,合金的晶体壳中存在少量的晶间非晶相,而非晶核中... 相似文献
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利用扩展x射线吸收精细结构和x射线衍射研究了机械合金化制备的体心立方(bcc)的亚稳态Fe80Cu20合金固溶体的结构随退火温度的变化特点.结果表明,在300—873 K温度范围内,随着退火温度的升高,bcc结构物相的晶格常数近于线性降低,这主要是由于Cu原子从bcc结构Fe80Cu20合金固溶体中逐渐偏析出来,生成面心立方(fcc)结构的Cu物相所致.经603K退火后,Cu原子的平均键长RCu—Cu增加了0.003 nm左右,大约有50%的Cu原子从bcc结构的Fe80Cu20合金固溶体中偏析出来.在773 K退火后,bcc结构Fe80Cu20合金固溶体近于完全相分离,生成了bcc结构的α-Fe与fcc结构的Cu物相.
关键词:
扩展x射线吸收精细结构
x射线衍射
80Cu20合金')" href="#">Fe80Cu20合金
机械合金化 相似文献
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测量了块体金属玻璃Zr46.75Ti8.25Cu7.5Ni10Be27.5在退火前后其电阻值随温度的变化,测量的温度范围为1.5—300K.样品在退火前后都发现有超导现象.零磁场下其超导转变温度Tc分别为1.84和3.76K.在5—300K温度范围内,原始样品具有负的电阻温度系数.如果取Zr, Ti, Cu, Ni及Be分别贡献出1.5, 1.5, 0.5, 0.5及两个传导
关键词:
块体金属玻璃
超导
电阻温度系数 相似文献
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应用同步辐射x射线小角散射法在原位对块体非晶合金Zr55Cu30Al 10Ni5在等温退火过程中的微结构变化进行研究.实验表明:在等温退火过程中电子 密度涨落反映了晶化之前的结构弛豫过程;在一定的退火温度下、随退火时间的增加,拓扑短程序弛豫与化学短程序弛豫之间存在一个电子密度均匀化的过程;导致这两种弛豫过程转变的退火时间与退火温度有关,温度越高,所需的退火时间越短.
关键词:
原位x射线小角散射
块体非晶合金
等温退火
结构弛豫 相似文献
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通过分析规则熔体的热力学模型,计算了典型金属玻璃的熔体混合焓ΔHmix和混合熵ΔSmix.结合临界冷却速率,归纳出典型金属玻璃形成液体的热力学特性,并提出基于原子尺寸、元素组成以及元素之间混合焓等参数的形成大块金属玻璃的成分判定方法.结果表明,当ΔHmix<-15 kJ·mol-1且ΔSmix>0.6 J·K-1mol-1时,合金易于形成大块金属玻璃.金属玻璃的临界冷却速率Rc具有明显的尺寸效应,其值与熔体的ΔSmix值呈指数关系,可以用Rc=42.24×104exp(-13.91ΔSmix)+19.66粗略判断.运用该方法成功设计并制备出远离原有Zr基大块金属玻璃形成区域(55at%—65at%Zr)的Zr40Al10Ni15Cu35和四元Fe-B基Fe53Co5Nd12B30大块金属玻璃.
关键词:
混合焓
混合熵
大块金属玻璃
玻璃形成能力 相似文献
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In the present work, the glass formation process and structural properties of Zr50Cu50-xCox (0 ≤ x ≤ 50) bulk metallic glasses were investigated by a molecular dynamics simulation with the many body tight-binding potentials. The evolution of structure and glass formation process with temperature were discussed using the coordination number, the radial distribution functions, the volume–temperature curve, icosahedral short-range order, glass transition temperature, Voronoi analysis, Honeycutt–Andersen pair analysis technique and the distribution of bond–angles. Results indicate that adding Co causes similar responses on the nature of the Zr50Cu50-xCox (0 ≤ x ≤ 50) alloys except for higher glass transition temperature and ideal icosahedral type ordered local atomic environment. Also, the differences of the atomic radii play the key role in influencing the atomic structure of these alloys. Both Cu and Co atoms play a significant role in deciding the chemical and topological short-range orders of the Zr50Cu50-xCox ternary liquids and amorphous alloys. The glass-forming ability of these alloys is supported by the experimental observations reported in the literature up to now. 相似文献
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In this paper, we systematically investigate local atomic structures of Zr100?x Al x (0???x???72) alloys using molecular dynamics simulations. Radial distribution functions of Zr-Al configurations at 300 K indicate that Zr-Al metallic glasses form only when the Al atomic concentration is larger than 32%. Voronoi polyhedral analysis shows that Zr40Al60 has the highest fraction of ?0,0,12,0? icosahedra around Al atoms, which are characteristic of amorphous microstructures. Variations of thermal expansion coefficient and heat capacity of Zr100?x Al x (40???x???72) metallic glasses as a function of temperature from 1100 to 800?K reveal that Zr40Al60 has the highest transition temperature of 1008?K. To confirm the simulation results, Zr-Al metallic glasses were fabricated using co-sputtering deposition; differential scanning calorimetry testing suggests the highest crystallisation-onset temperature of above 920?K is within Zr100?x Al x where 43?<?x?<?61. The experimental finding is in a good agreement with the simulation predictions. 相似文献
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Structural organization in the Cu<Subscript>80</Subscript>Zr<Subscript>20</Subscript> metallic glass
A. V. Korol’ A. T. Kosilov A. V. Milenin A. V. Evteev E. V. Levchenko 《Journal of Experimental and Theoretical Physics》2011,112(6):1013-1019
The laws of atomic restructuring in the Cu80Zr20 metallic glass during melt quenching are studied by molecular dynamics simulation using statistical-geometrical analysis
based on Voronoi polyhedra and cluster analysis. The morphology and size distribution of polyhedral nanoclusters in the glass
structure are investigated. 相似文献
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We report on the glass-forming ability and devitrification behavior of Zr60Cu30Al10, Zr60Cu25Al10Fe5 and Zr62.5Cu22.5Al10Fe5 bulk glass-forming alloys on heating. The effect of Fe addition on the structure of Zr–Al–Cu alloys is also discussed. Crystallization kinetics and structural changes in the glassy alloys were studied using X-ray diffraction, transmission electron microscopy, differential scanning and isothermal calorimetry methods. The results indicate that good glass-formers, such as Zr62.5Cu22.5Al10Fe5, are located somewhat beyond the equilibrium eutectic point. Possible phase separation in the supercooled liquid on heating and electron beam-induced in situ crystallization are observed and discussed. 相似文献
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Local atomic structures of Zr100−xNix (x=33.3, 36, 50 at%) binary metallic glasses were investigated by means of extended X-ray absorption fine structure (EXAFS) probe. Structural parameters show that the Zr-Ni bond length, RZr-Ni, keeps a constant value of 2.62 Å, regardless of alloy compositions. This result implies that there is a strongly chemical interaction between Zr and Ni atoms, leading to significant chemical short-range orders (CSROs) in the present metallic glasses. Further analysis indicates that the SRO structures in these metallic glasses are extremely similar with those in their crystalline counterparts. It is interesting to note that the CSROs in the eutectic Zr64Ni36 metallic glass consist of Zr2Ni-like and ZrNi-like CSROs. 相似文献
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Woyun Long Xueqiong OuyangZhiwei Luo Jing LiAnxian Lu 《Physica B: Condensed Matter》2011,406(3):503-507
Amorphous Zr50Al15−xNi10Cu25Yx alloy powders were fabricated by mechanical alloying at low vacuum with commercial pure element powders. The effects on glass forming ability of Al partial substituted by Y in Zr50Al15Ni10Cu25 and thermal stability of Si3N4 powders addition were investigated. The as-milled powders were characterized by X-ray diffraction, scanning electron microscopy and differential scanning calorimeter. The results show that partial substitution of Al can improve the glass forming ability of Zr50Al15Ni10Cu25 alloy. Minor Si3N4 additions raise the crystallization activation energy of the amorphous phase and thus improve its thermal stability. 相似文献
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Wen Deng ZhenYing Chen HaiFeng Jiang ShunPing Sun YingYing Zhu YuYang Huang 《中国科学G辑(英文版)》2008,51(9):1221-1228
Information of defects and 3d electrons in transition metals (Ti, V, Cu) and TiAl-based alloys (Ti50Al50, Ti50Al48V2, Ti50Al48Cu2) can be extracted from the positron lifetime and coincidence Doppler broadening spectra. The results show that the 3d electron
signals for the transition metals Ti, V and Cu increase with the number of 3d electrons. The 3d electron signal and the electron
density for binary TiAl alloy are relatively low due to the (Ti)3d-(Al)3p interactions. The addition of V and Cu atoms to
TiAl alloy leads to the increase in the electron densities in bulk and the defects on grain boundaries simultaneously, as
well as the enhancement of the 3d electron signal. The 3d electron signal in the spectrum of Ti50Al48Cu2 alloy is higher than that of Ti50Al48V2 alloy. 相似文献
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R. M. Khusnutdinoff A. V. Mokshin B. A. Klumov R. E. Ryltsev N. M. Chtchelkatchev 《Journal of Experimental and Theoretical Physics》2016,123(2):265-276
The structural and dynamic properties of the three-component Zr47Cu46Al7 system are subjected to a molecular dynamics simulation in the temperature range T = 250–3000 K at a pressure p = 1.0 bar. The temperature dependences of the Wendt–Abraham parameter and the translation order parameter are used to determine the glass transition temperature in the Zr47Cu46Al7 system, which is found to be Tc ≈ 750 K. It is found that the bulk amorphous Zr47Cu46Al7 alloy contains localized regions with an ordered atomic structures. Cluster analysis of configuration simulation data reveals the existence of quasi-icosahedral clusters in amorphous metallic Zr–Cu–Al alloys. The spectral densities of time radial distribution functions of the longitudinal (C?L(k, ω)) and transverse (C?T(k, ω)) fluxes are calculated in a wide wavenumber range in order to study the mechanisms of formation of atomic collective excitations in the Zr47Cu46Al7 system. It was found that a linear combination of three Gaussian functions is sufficient to reproduce the (C?L(k, ω)) spectra, whereas at least four Gaussian contributions are necessary to exactly describe the (C?T(k, ω)) spectra of the supercooled melt and the amorphous metallic alloy. It is shown that the collective atomic excitations in the equilibrium melt at T = 3000 K and in the amorphous metallic alloy at T = 250 K are characterized by two dispersion acoustic-like branches related with longitudinal and transverse polarizations. 相似文献
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Mg56Al30Li7Cu7 and Mg50Al30Y6Li7Cu7 melts were processed for 2 h in a centrifuge at an inertial acceleration of 60 000g and a temperature of 530°C. Subsequent slow cooling across the melting temperature during continuous centrifugation leads to a pronounced stratification, with primary phases forming at the sample ends and binary and ternary eutectic microstructures forming in the middle of the sample, as resolved by scanning electron microscopy. In both cases, the ternary eutectic has the approximate nominal composition Mg58Al33Li6Cu2.5(Y0.5). The implications of the use of high-temperature centrifugation as a new tool for finding deep eutectic compositions, which have the potential to form bulk metallic glasses, are discussed. 相似文献
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S. N. Aqida D. Brabazon S. Naher Z. Kovacs D. J. Browne 《Applied Physics A: Materials Science & Processing》2010,101(2):357-360
This paper presents a microstructural study of laser micro-processed high-purity Cu45Zr48Al7 alloys prepared by arc melting and Cu-mould casting. Microprocessing of the Cu45Zr48Al7 alloy was performed using a Rofin DC-015 diffusion-cooled CO2 slab laser system with 10.6-μm wavelength. The laser was defocused to a spot size of 0.2 mm on the sample surface. The laser
parameters were set to give 300- and 350-W peak power, 30% duty cycle and a 3000-Hz laser pulse repetition frequency (PRF).
About 100-micrometer-wide channels were scribed on the surfaces of disk-shaped amorphous and partially crystalline samples
at traverse speeds of 500 and 5000 mm/min. These channels were analysed using scanning electron microscopy (SEM) and 2D stylus
profilometry. The metallographic study and profile of these processed regions are discussed in terms of the applied laser
processing parameters. The SEM micrographs showed that striation marks developed at the edge and inside these regions as a
result of the laser processing. The results from this work showed that microscale features can be produced on the surface
of amorphous Cu–Zr–Al alloys by CO2 laser processing. 相似文献