首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到19条相似文献,搜索用时 156 毫秒
1.
根据用原子力显微镜对在不同温度下晶化的Fe基非晶合金薄带三维介观结构的观察,结合X射线衍射、Mssbauer谱等前人已有的实验结果并在目前已有的理论研究基础上,对Fe基非晶合金薄带在不同温度下的晶化过程进行了系统的分析、研究,提出了两种Nb-B框架介观结构、团聚相和单位体积纳米晶粒平均数等新概念,建立了Fe基纳米晶合金的晶化机理假说,提出了描述Fe基非晶合金晶化过程的介观织构模型.这个模型能够演化成二相结构模型和三相互套结构模型,还可以合理地解释现有的实验结果以及500—600℃退火中Fe基纳米晶巨磁阻 关键词: Fe基纳米晶合金 晶化机理 两种Nb-B框架介观结构 团聚相  相似文献   

2.
采用多晶材料趋近饱和定律研究了非晶Fe39.4-xCo40Si9B9Nb2.6Cux(x=O.5,1,1.5)合金在不同温度纳米晶化后的有效磁各向异性常数(K).结果表明,Cu含量较低(x=0.5)时,纳米晶粒较大并且在较低的退火温度(550℃)下析出硬磁相,(K)随退火温度Ta升高显著增加;随着Cu含量的增加,有效地细化了晶粒,并且抑制了硼化物的析出,(K)明显减小.讨论了(K)与晶粒尺寸D及初始磁导率的关系.  相似文献   

3.
杨静  王治  贾芸芸  韩叶梅 《物理学报》2010,59(11):8148-8154
研究了500和600℃真空退火后的纳米晶Fe38.4Co40Si9B9Nb2.6Cu合金初始磁导率随温度的变化规律,发现较高温度(600℃)退火的FeCo基纳米晶合金,在非晶相居里温度以上较宽温度范围内磁导率没有明显的衰减,这是在双相纳米晶合金中观察到的一种新现象,其磁特性不同于Fe基纳米晶合金.为了探明这种现象的起源,估算了与剩余非晶相同成分的非晶合金的居里温度及纳米晶粒间发生交换耦合作用的参数 关键词: 交换耦合作用 非晶相居里温度 交换耦合穿透深度  相似文献   

4.
张杨  宋晓艳  徐文武  张哲旭 《物理学报》2012,61(1):16102-016102
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   

5.
在晶化物理模型中添加扩散系数对晶化过程的影响, 采用相场方法研究初始形核率和初始形核半径对一次晶化过程中微观组织和生长动力学的影响。结果表明: 随着初始形核率的增加, 相同时间内非晶一次晶化的晶粒数量逐渐增加, 晶粒尺寸逐渐减小。晶化分数随着演化时间和初始形核率的增加逐渐增大, 初始形核率越大, 相同演化时间内的晶化分数越高。不同初始形核半径情况下, 非晶一次晶化过程中的晶粒数量和尺寸随着演化时间的增加基本保持不变。晶化分数随着演化时间的增加而增大。不同初始形核率和初始形核半径情况下所对应的生长指数均小于1, 表明初始形核率和初始形核半径对晶化方式无影响, 均为一次晶化。改变初始形核率和初始形核半径可调控一次晶化微观组织结构, 而晶粒尺寸及晶化分数直接关系到合金性能。  相似文献   

6.
采用成核 /晶化隔离法合成镁铁双羟基复合金属氧化物MgFe LDH ,考察了Mg∶Fe摩尔比对MgFe LDH晶形的影响 ,探讨了晶化温度及晶化时间对晶面生长选择性及晶粒尺寸的影响规律 .结果表明 ,随Mg∶Fe摩尔比增大 ,层板阳离子排列更为规整 .晶化温度对晶粒尺寸的影响显著大于晶化时间的影响 .晶化温度相同 ,随晶化时间延长 ,MgFe LDH的晶体结构趋于完整 ,晶粒尺寸变化不大 ;晶化时间相同 ,随晶化温度升高 ,晶体结构趋于完整 ,晶粒尺寸明显增大 .所得到的MgFe LDH沿a轴方向的晶粒尺寸对晶化温度变化的敏感程度远大于对晶化时间变化的敏感程度 ,但总是沿a轴方向的晶粒尺寸大于沿c轴方向的尺寸 ,即 [110 ]晶面的生长速率比[0 0 2 ]晶面的生长速率快  相似文献   

7.
韩献堂  王治  马晓华  王光建 《物理学报》2007,56(3):1697-1701
采用多晶材料趋近饱和定律研究了非晶Fe39.4-xCo40Si9B9Nb2.6Cux(x=0.5,1,1.5) 合金在不同温度纳米晶化后的有效磁各向异性常数〈K〉.结果表明, Cu含量较低(x=0.5)时,纳米晶粒较大并且在较低的退火温度(550℃)下析出硬磁相,〈K〉随退火温度Ta升高显著增加;随着Cu含量的增加,有效地细化了晶粒,并且抑制了硼化物的析出,〈K〉明显减小.讨论了〈K〉与晶粒尺寸D及初始磁导率的关系. 关键词: 纳米晶 有效磁各向异性 磁导率 FeCo基合金  相似文献   

8.
建立了纳米晶合金相的热力学模型,可定量描述纳米尺度下合金体系中化合物相的热力学性质,并预测合金相的稳定性及其转变规律.利用该模型全面计算了纳米晶Sm-Co合金体系中各化合物相在不同晶粒尺寸下的摩尔吉布斯自由能随温度的变化关系,预测了纳米尺度下Sm-Co合金体系中各物相的相对稳定性及转变规律.模型预测结果示出,在室温附近,随着纳米晶粒尺寸的减小,某些纳米晶合金相的摩尔吉布斯自由能将由负值变为正值,预示着将向其他更稳定的纳米晶合金相转变,这是与传统粗晶材料中合金相的稳定性仅依赖于温度条件而完全不同的纳米晶合金 关键词: 纳米晶材料热力学 Sm-Co合金 相稳定性 相变  相似文献   

9.
曹成成  范珏雯  朱力  孟洋  王寅岗 《物理学报》2017,66(16):167501-167501
研究了预退火时间对Fe_(80.8)B_(10)P_8Cu_(1.2)非晶合金微结构及磁性能的影响.穆斯堡尔谱研究表明:在660 K的预退火温度下,随着预退火时间的增加,Fe原子不断富集,非晶基体中的类Fe_3B化学短程有序结构向类Fe B结构转变,并且非晶基体中Fe第一近邻壳层中Cu原子的逐渐脱离以及Fe-P配位键数量的明显减少可间接表征CuP团簇的形成过程.同时,本研究通过调节预退火时间来调控非晶基体中CuP团簇和Fe团簇的数量,促进后续退火晶化过程中α-Fe纳米晶相的析出,并细化纳米晶尺寸,从而获得综合磁性能更加优异的非晶/纳米晶软磁合金.  相似文献   

10.
熊湘沅  何开元 《物理学报》1995,44(8):1286-1290
研究了经不同退火温度处理的Fe(?)Cu_2Nb_3Si_(?)B,纳米晶合金的有效磁各向异性〈k〉的变化,得出该合金在T_a=480—550℃之间退火后的有效磁各向异性〈k〉比相应成份的α-Fe(Si)固溶体晶粒的磁晶各向异性K_1小一个数量级,但随T_a的开高有效磁各向异性〈k〉只稍有变大,为860—910J.m~(-1),而起始磁导率在T_a=550℃时达到最大值.这一软磁性能的改善主要是由合金的磁致伸缩系数λ_(?)的明显变小造成的,而与有效磁各向异性〈k〉的变化无关. 关键词:  相似文献   

11.
The structural properties and parameters of ferromagnetic resonance have been studied for Fe73.5CuNb3Si13.5B9 nanocrystalline alloys produced from the initial amorphous state via annealing under different conditions. The dependence of the linewidth of the ferromagnetic resonance on the grain size ΔHD 6 has been found. The result is discussed within the framework of the random magnetic anisotropy model.  相似文献   

12.
陈慧敏  刘恩隆 《物理学报》2011,60(6):66501-066501
探讨了纳米颗粒和纳米块材摩尔定压热容 CP(T)的理论计算方法,提出了利用纳米颗粒的熔点数据来计算纳米颗粒的德拜(Debye)温度、体膨胀系数和CP(T)的理论公式,以铜纳米颗粒为例,CP(T)的理论计算值与实验值符合较好;提出了纳米块材的Debye温度随块材密度变化的关系式,随着块材密度减小,Debye温度降低;铜纳米块材CP(T)的理论计算值与实验值也符合较好;纳米块材的体 关键词: 纳米颗粒 纳米块材 CP(T)')" href="#">摩尔定压热容CP(T) 德拜温度  相似文献   

13.
The structural and electrical conductivity (σ) of annealed SrTiO3–PbO2–V2O5 glasses were studied. The annealing of initially glass samples leads to formation of nanocrystalline grains embedded in the glassy matrix. XRD patterns of the glass–ceramic samples show that nanocrystals were embedded in the glassy matrix with an average grain size of 32 nm. The glass–ceramic nanocrystals obtained by annealing at temperatures close to the crystallization temperature Tc exhibit enhancement of electrical conductivity up to four orders of magnitude than initially glasses. The enhancement of the electrical conductivity due to annealing was attributed to two interdependent factors: (i) an increase of concentration of V4+–V5+ pairs; and (ii) formation of defective, well-conducting regions along the glass–crystallites interfaces. From the conductivity temperature relation, it was found that small polaron hopping model was applicable at temperature above θD/2 (θD, the Debye temperature). The electrical conduction at T >θD/2 was due to non-adiabatic small polaron hopping (SPH) of electrons between vanadium ions. The parameters obtained from the fits of the experimental data to this model appear reasonable and are consistent with glass composition.  相似文献   

14.
Electrodeposited nanocrystalline Co offers a relatively unique opportunity to study the interaction of two fundamentally different elementary solid state reactions: grain growth and ε (HCP) to α (FCC) allotropic phase transformation. Samples were isothermally annealed at temperatures above and below the equilibrium transformation temperature (Tεα?=?695?K) and quenched to ambient for subsequent characterization by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Isothermal annealing above 695?K resulted in concurrent grain growth and ε to α transformation. Unexpectedly, however, simultaneous grain growth and ε to α transformation also occurred during isothermal annealing at temperatures as low as 573?K, i.e. 122?K below the expected equilibrium Tεα. It was observed that non-equilibrium α-Co formed within a matrix of nanocrystalline ε-Co via abnormal grain growth, and is therefore fundamentally different from the ε to α transformation typically observed in conventional polycrystalline Co.  相似文献   

15.
Structure, hyperfine interactions, and magnetic behaviour of Fe80M7Cu1B12 (M=Mo, Nb, Ti) nanocrystalline alloys are studied by Mössbauer spectrometry. As-quenched and heat-treated specimens are investigated. Transmission and Conversion Electron Mössbauer effect techniques are used to compare surface and bulk crystallization as a function of annealing temperature with the aim to unveil the crystallization onset. In addition, magnetic structure comprising distributions of hyperfine fields is discussed as a function of composition and annealing temperature. Hyperfine field distributions are obtained separately for the amorphous residual phase and for interface regions. Crystalline phases are represented by discrete components.  相似文献   

16.
In order to clarify the origin of the high thermal stability of the microstructure in bcc-Fe/amorphous two-phase nanocrystalline soft magnetic materials, we have investigated the changes in the magnetic and microstructural properties upon isothermal annealing at 898 K for an Fe89Zr7B3Cu1 alloy by means of transmission electron microscopy, Mössbauer spectroscopy and DC magnetometry. The mean grain size was found to remain almost unchanged at the early stage of annealing. However, rapid grain coarsening was evident at an annealing time of 7.2 ks where the intergranular amorphous phase begins to crystallize into Fe23Zr6. The grain growth process with a kinetic exponent of 1.6 is observed for the growth process beyond this annealing time, reflecting the disappearance of the intergranular amorphous phase. Our results confirm that the thermal stability of the bcc-Fe/amorphous two-phase nanocrystalline soft magnetic alloys is governed by the residual amorphous phase.  相似文献   

17.
Glass-forming ability (GFA) and thermal stability of Fe62Nb8B30, Fe62Nb6Zr2B30 and Fe72Zr8B20 at % amorphous alloys were investigated by calorimetric (DSC and DTA) measurements. The crystallization kinetics was studied by DSC in the mode of continuous versus linear heating and it was found that both the glass transition temperature, T g , and the crystallization peak temperature, T p , display strong dependence on the heating rate. The partial replacement of Nb by Zr leads to lower T g and T x temperatures and causes a decrease of the supercooled liquid region. JMA analysis of isothermal transformation data measured between T g and T x suggests that the crystallization of the Fe62Nb8B30 and Fe62Nb6Zr2B30 amorphous alloys take place by three-dimensional growth with constant nucleation rate. Nb enhances the precipitation of the metastable Fe23B6 phase and stabilizes it up to the third crystallization stage. Zr addition increases the lattice constant of Fe23B6 and, at the same time, decreases the grain size.  相似文献   

18.
Radiography, differential scanning calorimetry, luminescence and high-resolution electron microscopy are used to study the production, nanocrystalline structure, stability, and microhardness of alloys from the Ni-Mo-B system containing from 27 at. % to 31.5 at. % Mo and 10 at. % B. All studies of these alloys indicated that annealing at 600 °C leads to the creation of a granular phase consisting of FCC nanocrystallites with average grain sizes of 15–25 nm, depending on the chemical composition of the alloy. Annealing these nanocrystalline samples isothermally at a temperature of 600 °C has no appreciable effect on the grain size. Structurally, the nanocrystalline phase consists of grains of an FCC solid solution of Mo and B in Ni, dispersed in an amorphous matrix that isolates them from one another. The lattice parameters of the FCC nanocrystallites depend on the alloy composition and the duration of their isothermal anneal. Within this latter time, molybdenum and boron atoms diffuse from the FCC solid-solution lattice into the surrounding amorphous matrix. The stability of the nanocrystalline structure is determined by the thermal stability of the amorphous matrix, whose crystallization temperature increases with the isothermal annealing time due to enrichment by boron and molybdenum. As the structure forms, the alloy becomes harder as the nanocrystalline grains grow in size. This relation between hardness and grain size, which is opposite to the Hall-Petch law, is explained by hardening of the amorphous matrix due to changes in its chemical composition. Fiz. Tverd. Tela (St. Petersburg) 40, 10–16 (January 1998)  相似文献   

19.
Nanocrystalline materials contain many atoms at and near grain boundaries. Sufficient numbers of Mössbauer probe atoms can be situated in grain boundary environments to make a clear contribution to the measured Mössbauer spectrum. Three types of measurements on nanocrystalline materials are reported here, all using Mössbauer spectrometry in conjunction with X-ray diffractometry, transmission electron microscopy, or small angle neutron scattering. By measuring the fraction of atoms contributing to the grain boundary component in a Mössbauer spectrum, and by knowing the grain size of the material, it is possible to deduce the average width of grain boundaries in metallic alloys. It is found that these widths are approximately 0.5 nm for fcc alloys and slightly larger than 1.0 nm for bcc alloys. Chemical segregation to grain boundaries can be measured by Mössbauer spectrometry, especially in conjunction with small angle neutron scattering. Such measurements on Fe-Cu and Fe3Si-Nb were used to study how nanocrystalline materials could be stabilized against grain growth by the segregation of Cu and Nb to grain boundaries. The segregation of Cu to grain boundaries did not stabilize the Fe-Cu alloys against grain growth, since the grain boundaries were found to widen and accept more Cu atoms during annealing. The Nb additions to Fe3Si did suppress grain growth, perhaps because of the low mobility of Nb atoms, but also perhaps because Nb atoms altered the chemical ordering in the alloy. The internal structure of grain boundaries in nanocrystalline materials prepared by high-energy ball milling is found to be unstable against internal relaxations at low temperatures. The Mössbauer spectra of the nanocrystalline samples showed changes in the hyperfine fields attributable to movements of grain boundary atoms. In conjunction with SANS measurements, the changes in grain boundary structure induced by cryogenic exposure and annealing at low temperature were found to be somewhat different. Both were consistent with a sharper density gradient between the crystalline region and the grain boundary region.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号