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排序方式: 共有459条查询结果,搜索用时 31 毫秒
21.
The FePt system has important perspectives as high-temperature corrosion-resistant magnets. In the form of rapidly solidified melt-spun ribbons, FePt-based magnets may exhibit in certain cases a two-phase hard–soft magnetic behaviour. The present paper deals with a microstructural and magnetic study of FePtAgB alloys with increasing Ag content. The aim is to identify and confirm the effect of Ag addition in decreasing the temperature of the FePt disorder–order structural phase transformation. A detailed high-resolution transmission electron microscopy study is employed, and the alternative disposal of hard and soft regions within the two-phase microstructure is observed and interpreted with respect to the X-ray diffraction results. In the as-cast Ag-containing samples, it is shown that there is an optimum of the Ag content for which best magnetic properties are obtained. Ag addition creates a nonlinear behaviour of the coercive field and the ordering parameter, similar to the RKKY interaction-induced interlayer exchange coupling (IEC) observed in magnetic layers separated by non-magnetic spacer layers. Direct formation of the L10 phase from the as-cast state in the FePtAgB alloys is reported with magnetic parameters compatible to other exchange spring permanent nanomagnets. These findings open novel perspectives into utilization of such alloys in applications requiring magnets operating in high-temperature industrial environments. 相似文献
22.
M. Kambara K. Miyake K. Murata T. Izumi Y. Shiohara T. Umeda 《Physica C: Superconductivity and its Applications》2000,330(3-4):191-202
Crystal growth of the melt-textured bulk Nd1+xBa2−xCu3O6+d (Nd123) superconducting oxides was investigated by employing isothermal undercooling solidification with hot-seeding in air. From the relationship between growth length and holding time, the Nd123 crystal was found to have almost stopped growing after a certain growth period, while the growth length increased proportionally to the holding time at an early stage of the crystal growth. As a result of quantitative analysis for the Nd123 crystal of which solidification was terminated, the distribution of the Nd/Ba substitution was observed to decrease in the Nd123 single crystal matrix from the seed crystal to the edge of the Nd123 crystals. Also, the substitution content at the edge of the Nd123 crystal, which corresponds to that at the final stage of the crystal growth, was found to be in good agreement with the minimum substitution of the Nd123 solid solution phase in the equilibrium phase diagram at this process temperature. These compositional changes could be explained using the equilibrium phase diagram as associated with the solid solution formation, which is responsible for the non-steady state solidification of the Nd123 crystals even for the isothermal undercooling processing. 相似文献
23.
Rapid solidification processing (cooling rate from the interval 105–106 K s−1) was used to prepare deeply undercooled cryolite-alumina melts. Such prepared samples were analyzed by the XRD method. Besides
cryolite, XRD patterns belonging to ι-Al2O3 were recorded. The influence of annealing on the XRD patterns of deeply undercooled melts was also investigated. 相似文献
24.
Michal Korenko Marián Kucharík Jozef Vincenc Oboňa Dušan Janičkovič Rosa Córdoba José María De Teresa Blanka Kubíková 《Helvetica chimica acta》2008,91(7):1389-1399
The rapid‐solidification processing (by a cooling rate of 105–106 K/s) was used for the preparation of deeply undercooled cryolite/alumina (Na3AlF6/Al2O3) melts. We found a mass of nanotubes on the surface of these undercooled melts. The nanotubes were preferentially located on the defect places of the surface with the following approximate dimensions: base≈100×100 nm, length≈1000 nm. The solidified samples with the nanotubes on the surface were analyzed by scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy (EDX), X‐ray diffraction (XRD), and infrared spectroscopy (IR). 相似文献
25.
R. M. Shalaby 《Crystal Research and Technology》2010,45(4):427-432
The Sn‐Zn alloys have been considered as lead‐free solders. In this paper, the effect of 0.0, 0.5, 1.0, 1.5 and 2.0 wt.% Indium as ternary additions on melting temperature, structure, microhardness and micro‐creep of the Sn‐9Zn lead‐free solders were investigated. It is shown that the alloying additions of Indium to the Sn‐Zn binary system result in a suppression of the melting point to 187.9 °C. From x‐ray diffraction analysis, a new intermetallic compound phase, designated β‐In3Sn is detected. The formation of an intermetallic compound phase causes a pronounced increase in the electrical resistivity and mechanical strength. Also, an interesting connection between dynamic Young's modulus and the axial ratio (c/a) of the unit cell of the β‐Sn was found in which Young's modulus increases with increasing the axial ratio (c/a). The ternary Sn‐9Zn‐xIn exhibits creep resistance superior to Sn‐9Zn binary alloy. The better creep resistance of the ternary alloy is attributed to solid solution effect and precipitation of In3Sn in the Sn matrix. The addition of small amounts of In is found to refine the effective grain size and consequently, improves hardness. The 89%Sn‐9%Zn‐2%In alloy is a lead‐free solder designed for possible drop‐in replacement of Pb‐Sn solders. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
26.
采用分子动力学模拟方法模拟了在周期性边界条件下由500个原子构成的液态Mg模型系统的凝固过程,分别考察了在5×10^14 K/s、5×10^13 K/s、1×10^13 K/s 、1×10^12 K/s的冷却速率下液态Mg熔体的凝固行为。模拟结果很好地重现了实验值。模拟中原子间作用势采用FS势,结构分析采用径向分布函数、均方位移、系统总能量分析、H-A键对分析技术等方法。结果表明,当冷却速率为5×10^14 K/s时,系统形成以1541键对为主的非晶态结构;当冷却速率分别为5×10^13 K/s、1×10^13 K/s、1×10^12 K/s时,系统形成以1421、1422键对为主的hcp晶态结构;另外,在快速冷却形成非晶的过程中,大部分bcc结构被保留下来,而在慢冷形成晶态的过程中,大部分bcc结构最终演化形成了hcp结构。 相似文献
27.
28.
在自由落体条件下实现了三元Co-Cu-Pb合金的液相分离与快速凝固. 实验发现,随液滴直径减小,Co51Cu47Pb2合金液滴发生由枝晶→两层壳核→枝晶组织的转变,Co47Cu44Pb9合金液滴的组织形态由壳核组织演化为均匀组织. 两种合金的快速凝固组织均由α(Co),(Cu)和(Pb)固溶体三相组成,α(Co)和(Cu)相主要以枝晶方式生长,(Pb)相分布在(Cu)枝晶间.
关键词:
液相分离
偏晶合金
快速凝固
自由落体 相似文献
29.
Dongmei Liu Yanqing SuXinzhong Li Liangshu LuoJingjie Guo Hengzhi Fu 《Journal of Crystal Growth》2010,312(24):3658-3664
Experiments on Al–25 at%Ni peritectic alloy consisting of melting followed by thermal stabilization ranging from 0 to 2 h were carried out in a Bridgman-type furnace. Temperature distribution, microstructure evolution and solute concentration in the mushy zone are characterized. An analytical model is proposed to evaluate the Ni concentration of the melt after thermal stabilization. Effect of temperature gradient and volume fraction of liquid phase in the mushy zone on the Ni concentration of the melt is discussed. The steady state Ni concentration of the melt is inappropriately below the initial Ni concentration of the sample. The deviation increases with decreasing temperature gradient. Finally, the influence of thermal stabilization on the solute concentration of the melt is discussed based on a comparison of Al–Ni peritectic alloys with Al–Ni hyper-eutectic alloys and Al–Cu hypo-eutectic alloys. 相似文献
30.
In this article, under certain conditions, we prove the regularity for the solutions of an Allen–Cahn phase‐field type system obtained as limits of approximate solutions constructed by using a semidiscrete spectral Galerkin method. With the help of this improved regularity, as one compares to previous results, we then derive error estimates for the approximate solutions in terms of the inverse of the eigenvalues of the Laplacian operator. The system under investigation may model the evolution of solidification or melting of certain binary alloys. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献