Effects of nickel on the crystallization of Zr70Cu20Ni10 amorphous alloy

Differential scanning calorimetry (DSC) and x-ray diffraction (XRD) are employed to investigate the effects of nickel on the crystallization of the amorphous Zr₇₀Cu₂₀Ni₁₀ alloy. We have found that the crystallization process of the amorphous Zr₇₀Cu₂₀Ni₁₀ alloy is strongly influenced by the addition of nickel. Addition of 10 at% Ni to the Zr₇₀Cu₃₀ amorphous alloy makes the crystallization process proceed from a single-stage mode to a double-stage mode. The activation energy for crystallization of the amorphous Zr₇₀Cu₂₀Ni₁₀ alloy is calculated to be about 388kJ·mol^-1 on the basis of the Kissinger equation. The effects of nickel on the crystallization of the amorphous Zr₇₀Cu₂₀Ni₁₀ alloy are discussed in terms of the genetics of metals.     

Temperature dependence of the coercivity in Nd60Fe30−xCoxAl10, x=0 or 10, and Pr58Fe24Al18 bulk amorphous ferromagnets

Bulk amorphous ferromagnet alloys of composition Nd₆₀Fe₃₀Al₁₀, Nd₆₀Fe₂₀Co₁₀Al₁₀ and Pr₅₈Fe₂₄Al₁₈ have been prepared by argon arc melting and quenching into a copper mould. General insight into the magnetic behaviour of the alloys was gained from measurement of the major hysteresis loop at room temperature, and from zero-field cooled and field-cooled magnetisation measurements in the range 10-400 K. Measurements of the coercivity were made from 10 to 400 K, and for all alloys, the coercivity is seen to increase steeply with decreasing temperature to a peak at a temperature in the range 25-50 K, before decreasing. For all alloys, the temperature dependence of the coercivity between 50 and 400 K is well explained by the strong pinning model of domain walls of Gaunt [Philos. Mag. B 48 (1983) 261]. Quantities deduced from the Gaunt model, along with other relevant magnetic parameters, are used to estimate values for the exchange and anisotropy constants.     

Magnetic viscosity in Nd60Fe30Al10 amorphous alloys

Ferromagnetic amorphous Nd₆₀Fe₃₀Al₁₀ alloys melt spun at wheel speeds between 5 and 20 m/s exhibit hard magnetic properties, which are found to be very sensitive to the cooling conditions. The magnetization reversion mechanisms leading to the rather high coercive forces found are investigated by thermally activated magnetic relaxation experiments; the mean fluctuation field and the activation volume are measured—in specimens cooled at different rates—at the critical field for extensive magnetization reversion. These preliminary results show a qualitative agreement with the predictions of a ferromagnetic cluster model.     

Zr60Al15Ni25大块非晶合金晶化动力学研究

通过等温示差扫描量热法研究了Zr₆₀Al₁₅Ni₂₅大块非 晶合金的晶化动力学.实验结果表明，晶化过程的孕育期很短，即使在743 K这样低的温度下也不过0.52 min，而放热峰宽（反应整个晶化过程进行的时间）却随退火温度的降低明显增大，这说明了结晶过程是一个晶核长大控制的过程.Avrami指数表明在不同的退火温度，该合金的晶化机制发生了变化.晶化机制的变化是由于合金原子在不同温度下的扩散能力相差很大所致. 关键词： 晶化动力学 60Al₁₅Ni₂₅大块非晶合金')" href="#">Zr₆₀Al₁₅Ni₂₅大块非晶合金 示差扫 描量热法（DSC）     

非晶态Gd45Ni30Al15Co10合金的制备与磁热性能

具有优良磁热性能的材料是磁制冷技术应用的关键.本文设计制备出了一种非晶态四元Gd₄₅Ni₃₀Al₁₅Co₁₀合金条带,系统地研究了该合金的磁热性能. Co的引入增加了合金的非晶态热稳定性,扩大了过冷液相区宽度. Gd₄₅Ni₃₀Al₁₅Co₁₀非晶态合金条带的居里温度和有效磁矩分别为80 K和7.21μB,在10 K温度下饱和磁化强度达到173 A·m~2·kg^-1,矫顽力为0.8 kA·m^-1,具有优异的软磁性能.在5 T的外加磁场下, Gd₄₅Ni₃₀Al₁₅Co₁₀非晶态合金的磁熵变峰值和相对制冷能力分别高达10.2 J·kg^-1·K^-1和918 J·kg^-1.该合金具有典型的二级磁相变特征,可以在较宽的温度范围...     

Cu60Zr30Ti10非晶合金弛豫和晶化过程的小角X射线散射研究

应用小角X射线散射技术研究了Cu₆₀Zr₃₀Ti₁₀非晶合金从300到813 K之间微结构的演化情况.发现在淬火状态下Cu₆₀Zr₃₀Ti₁₀非晶合金中存在直径30 nm左右的富Cu区.非晶的结构弛豫包括573 K之前的低温结构弛豫和573 K到玻璃转变温度的高温结构弛豫，弛豫的结果是产生含有有序原子团簇的富Cu区，这些有序原子团簇的富Cu区是随后晶化过程中晶核产生的基础.Porod曲线分析表明，晶化生成的纳米体心立方CuZr相和基体之间有明锐的界面. 关键词： 小角X射线散射 非晶合金 结构弛豫 晶化     

水雾化制备Fe74Al4Sn2P10C2B4Si4非晶合金粉末及其磁粉芯性能研究

采用水雾化方法制备Fe₇₄Al₄Sn₂P₁₀C₂B₄Si₄合金粉末，研究发现该合金具有强的非晶形成能力和高热稳定性，在粉末粒度小于400目时可以形成非晶态合金.采用该非晶粉末制备的磁粉芯在高频下品质因数显著高于MPP粉芯，说明该磁粉芯高频损耗较低.分析表明，非晶合金磁粉芯高频下损耗低的主要原因是电阻率较高. 关键词： 非晶合金 磁粉芯 玻璃形成能力 软磁性能     

粉末状态对激光立体成形Zr55Cu30Al10Ni5块体非晶合金晶化行为的影响

基于金属熔体结构的遗传性, 激光熔池的快速熔凝导致粉末的晶化状态可能会对最终成形件的晶化产生重要影响, 理清其影响规律对于制备大块非晶合金具有重要意义. 本文选取等离子旋转电极法所制粉末和1000 K退火态粉末为沉积材料, 采用激光立体成形技术沉积Zr₅₅Cu₃₀Al₁₀Ni₅块体非晶合金, 考察了粉末中已有晶化相对熔池及热影响区晶化行为的影响. 结果发现, 原始粉末组织由非晶相及粗大的Al₅Ni₃Zr₂相组成; 当激光线能量较低时, 相应熔覆层的熔池和热影响区皆含有Al₅Ni₃Zr₂相; 随着线能量的提高, 熔池中Al₅Ni₃Zr₂相消失, 保持了非晶态, 但热影响区晶化加重, 并有大量Al₅Ni₃Zr₂相析出; 当采用退火态粉末时, 即使线能量较小, 相应熔覆层仍主要由非晶构成, 几乎无Al₅Ni₃Zr₂相析出. 这是由于原始粉末在退火时其微观结构发生重排, 与Al₅Ni₃Zr₂相关的原子短程/中程有序结构减少, 导致已沉积层非晶区的热稳定性提高, 不利于Al₅Ni₃Zr₂相析出. 可见, 提高线能量将会加剧非晶沉积体的晶化, 而粉末中的Al₅Ni₃Zr₂团簇相状态对Zr₅₅Cu₃₀Al₁₀Ni₅合金沉积层的晶化有重要影响.     

Microstructure and hard magnetic properties in bulk rods of Nd60Fe30Al10 glass forming alloys

The Nd₆₀Fe₃₀Al₁₀ alloy exhibits a large glass forming ability which allows to obtain relatively thick cast rods containing large volume fractions of amorphous phases. In this work the microstructure and the hard magnetic properties of as-cast rods are characterized. The alloy is processed by suction casting into a chilled copper mould to obtain cylinders 5 mm diameter and 50 mm length. This diameter is selected because it is an upper limit for this processing route, beyond which the hard properties largely deteriorate. A room temperature coercivity of 0.34 T is obtained. The sample microstructure is heterogeneous, with very different size scales near the surface and along the central zone. However, in both regions a large fraction of an amorphous ferromagnetic phase is observed; it is found that paramagnetic nanocrystalline phases – mainly Nd or Nd-rich particles, embedded in the amorphous matrix – are somewhat coarser in the central zone. These larger nanocrystals, less efficient to pin domain walls, are proposed to be responsible for the lower coercive fields observed, as compared with those found in cylinders 1–3 mm diameter where no inhomogeneities are found. This conclusion is supported by microstructure, calorimetric and magnetic observations.     

退火态Zr55Al10Ni5Cu30块体非晶合金在轧制过程中的自由体积演化

将Zr₅₅Al₁₀Ni₅Cu₃₀块体非晶合金在715 K等温退火30 min, 引入少量纳米晶, 然后于室温以不同的应变速率进行轧制, 用差示扫描量热仪考察不同应变量样品的热稳定性和自由体积演化. 结果表明:即使轧制到95%的最大应变量, 样品的热稳定性也几乎没有发生改变. 在各种应变速率下, 随着应变量的增加, 自由体积含量持续上升. 但随着应变速率的增加, 相同应变量下自由体积的含量先上升后降低, 该规律与单一非晶态结构合金在塑性变形过程中自由体积的变化情况截然不同.     

Effect of processing parameters on the structure and magnetic properties of Nd60Fe30Al10 alloy

Although rapidly solidified Nd–Fe–Al alloys exhibit hard magnetic properties they so far have not found any practical application, however, their study has great scientific meaning. Investigations of the Nd–Fe–Al alloys enable one to evaluate the effect of magnetic interactions, between nanoscale precipitates, having different structure and properties, on the macroscopically observed phenomena. The evolution of microstructure in the course of annealing is generally unclear. Most of the reported data were obtained for different materials, using various processing methods, which makes their comparison difficult. It was shown that different fabrication methods (melt spinning, suction casting) generate different properties. On the other hand, for the particular processing method the structure and magnetic properties are highly affected by the processing variables.

In this study the samples fabricated by two methods were compared. Melt spinning, with the roll speed 5–30 m/s, and casting into moulds having bore diameters 1, 3, 6 and 12 mm were used. The alloy composition was kept constant Nd₆₀Fe₃₀Al₁₀. Strong dependence of the magnetic properties on quenching rate was proved. Application of the appropriate processing variables for both the methods (roll speed or rode diameter) enables one to obtain comparable quenching rates and thus overall similar magnetic properties. However, for the cylindrical specimens different cooling rates for the surface and core produces a structural gradient, which leads to variation of the magnetic properties on the sample cross-section. The structural and property gradients were evaluated using SEM and magnetic measurements, respectively.     

压力对Zr46.75Ti8.25Cu7.5Ni10Be27.5大块非晶合金玻璃转变和晶化动力学的影响

利用X射线衍射和差示扫描量热分析研究了高温高压下Zr_46.75Ti_8.25Cu_7.5Ni₁₀Be_27.5大块非晶合金的玻璃转变和晶化行为，结果发现压力降低了该大块非晶合金中的自由体积、热焓和晶化激活能. 关键词： 大块非晶合金 高压 差示扫描量热分析 玻璃转变     

Nonlinear elastic characteristics of Zr52.5Ti5Cu17.9Ni14.6Al10 and Pd40Cu30Ni10P20 bulk metallic glasses

The influence of uniaxial compression on the propagation of sound in Zr_52.5Ti₅Cu_17.9Ni_14.6Al₁₀ and Pd₄₀Cu₃₀Ni₁₀P₂₀ bulk metallic glasses is investigated, and the third-order elastic moduli of these glasses are determined. __________ Translated from Fizika Tverdogo Tela, Vol. 47, No. 3, 2005, pp. 395–399. Original Russian Text Copyright ? 2005 by Kobelev, Kolyvanov, Khonik.     

A comparative study of FMR and Brillouin light scattering on amorphous Fe40Ni40B20

It is shown that magnetic surface mode frequencies in the amorphous ferromagnet Fe₄₀Ni₄₀B₂₀ measured using Brillouin light scattering depend upon the incident laser light intensity: presumably due to local heating of the specimen due to the concentration of the light flux into a focal spot only a few microns in diameter. Surface mode frequencies extrapolated to zero light intensity are shown to be consistent with magnetic parameters measured using ferromagnetic resonance at 35.731 GHz to within ±0.5 GHz for specimens of amorphous Fe₄₀Ni₄₀B₂₀. 0.5 GHz corresponds to a change of 0.17 kG in the saturation magnetization, 4πM_s.     

Research on Zr50Al15−xNi10Cu25Yx amorphous alloys prepared by mechanical alloying with commercial pure element powders

Amorphous Zr₅₀Al_15−xNi₁₀Cu₂₅Y_x 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.     

Thermomagnetic transitions and coercivity mechanism in bulk composite Nd60Fe30Al10 alloys

The thermomagnetic behaviour (within the temperature range 553-300 K) for the bulk composite Nd₆₀Fe₃₀Al₁₀ alloy is described in terms of a transition from paramagnetic to superferromagnetic state at T=553 K, followed by a ferromagnetic ordering for T<473 K. For the superferromagnetic regime, the alloy thermomagnetic response was associated to a homogeneous distribution of magnetic clusters with mean magnetic moment and size of 1072 μ_B and 2.5 nm, respectively. For T<473 K, a pinning model of domain walls described properly the alloy coercivity dependence with temperature, from which the domain wall width and the magnetic anisotropy constant were estimated as being of ≈8 nm and ≈10⁵ J/m³, typical values of hard magnetic phases. Results are supported by microstructural and magnetic domain observations.     

1at％ Ag替代Zr57Cu20Al10Ni8Ti5金属玻璃中各组元对玻璃形成能力及热稳定性的作用分析

以1at％ Ag元素分别等量替代Zr57Cu20Al10Ni8Ti5金属玻璃的各个组元,利用差示扫描量热升温分析获得不同试样的热力学参数,并结合不同尺寸(Φ8,Φ10,Φ12)吸铸试样的X-射线衍射分析结果,考察、验证元素替代后合金的实际玻璃形成能力及热稳定性的变化规律.经比较发现,Ag替代Ti元素,其玻璃形成能力显著提高(直径实际增大4 mm),同时热稳定性也明显改善,且临界冷却速率也明显降低,而Ag替代其他组元却无明显规律.针对玻璃形成能力的相关数据比较分析表明,本文结果未显示符合其Inoue的尺寸准则,混合焓判据也未显示出明显符合的现象.通过对堆垛密度的计算发现,1 at％ Ag替代Ti元素后使金属玻璃体系内部的堆垛密度增加.通过动力学分析,从晶化激活能、晶化反应速率常数两方面探讨了元素替代对玻璃形成能力和热稳定性的作用机理.     

Electronic structure and structural stability of LaAl2 and LaAl3—A comparative study

The large structural stability regime of LaAl₂ and LaAl₃ as a function of pressure is investigated by the band structure calculations using the FP-LAPW method. An earlier experimental study has revealed that there is no structural phase transition at ∼35 and ∼30 GPa for LaAl₂ and LaAl₃, respectively. Our calculations indicate that in the density of states curve of LaAl₂, the Fermi level (E_F) lies in a slope between bonding maxima and antibonding minima. At high pressures the E_F moves slightly towards the valley, but this shifting does not affect its structural stability. In LaAl₃, the E_F falls in a flat region in the density of states and does not move even up to 33 GPa. The band dispersion curves for both the compounds show movement of bands under the influence of pressure. Some of them cross the Fermi level leading to so called Lifshitz transitions. However, it is seen that these electronic changes do not manifest into any volume anomaly in LaAl₃ under pressure. Our study clearly shows that the density of states behavior for LaAl₂ and LaAl₃ satisfies the Yamashita-Asano criterion for structural stability. The theoretical equations of state, bulk modulus and its pressure derivative values are compared with the experimental values.     

Ab initio electronic structure,bonding and optical properties of two relatively new ceramics Hf2Al3C4 and Hf3Al3C5: A comparative study

The structural, electronic and optical properties of the ternary carbides Hf₂Al₃C₄ and Hf₃Al₃C₅ are studied via first principles orthogonalized linear combination of atomic orbitals (OLCAO) method. Results on crystal structure, interatomic bonding, band structure, total and partial density of states (DOS), localization index (LI), effective charge (Q*), bond order (BO), dielectric function (ε), optical conductivity (σ) and electron energy loss function are presented and discussed in detail. The band structure plots show the conducting nature of Hf₂Al₃C₄ and Hf₃Al₃C₅ carbides. DOS results disclose that the total number of states at Fermi level N(E_F) are 1.89 and 2.38 states/(eV unit cell) for Hf₂Al₃C₄ and Hf₃Al₃C₅ respectively. The Q* calculations show an average charge transfer of 0.723 and 0.711 electrons from Hf and 0.809 and 0.807 electrons from Al to C sites in Hf₂Al₃C₄ and Hf₃Al₃C₅ respectively. The BO results provide the dominating role of Al–C bonds with BO value of 6.62 (BO%?=?59%) and 6.66 (BO%?=?49%) for Hf₂Al₃C₄ and Hf₃Al₃C₅ respectively and are considered responsible for the crystals cohesion. The LI results reflect the presence of highly delocalized states in the vicinity of the Fermi level. The dielectric function plots of the real (?₁(?ω)) and imaginary (?₂(?ω)) parts show the anisotropic behavior of Hf₂Al₃C₄ and Hf₃Al₃C₅. The results on optical conductivity (σ) support the trends observed in dielectric functions. The electron energy loss functions reveal the presence of sharp peaks both in ab-plane and along c-axis around 20?eV in Hf₂Al₃C₄ and Hf₃Al₃C₅ ternary carbides.     

A comparative study of electronic structure and magnetic properties of SrCrO3 and SrMoO3

A comparative study of electronic structure and magnetic properties of SrCrO₃ and SrMoO₃ has been carried out using FPLAPW method with density-functional theory. The calculated results suggest that both compounds are nonmagnetic (NM) metal in cubic structures at room temperature, and they exhibit very similar band structure and electronic properties except more extend Mo 4d orbitals than Cr 3d electronic states. However, the electronic structure and magnetic properties exhibit remarkable differences between them in the low temperature phases. SrCrO₃ is with a C-AFM ground state with magnetic moment of 1.18μ_B/Cr in the tetragonal structure, while SrMoO₃ is with a NM ground state in the orthorhombic structure. It is assumed that the extend 4d orbitals may be the reason which results in NM solution at low temperature phase of SrMoO₃.