Heat treatment effects in amorphous metals: Zr70Cu30 and La70Cu30

We measured the electrical resistivity (4–300 K), superconducting critical temperature and thermal conductivity (0.5–7 K) of the amorphous metals Zr₇₀Cu₃₀ and La₇₀Cu₃₀. Heat treatments below crystallization temperature induced changes in these properties. In particular, in the first stage of the annealing of Zr₇₀Cu₃₀ there are systematic changes in the thermal conductivity and the critical temperature, while the electrical resistivity remains constant. We show that there is no simple correlation between the thermal conductivity processes in the low temperature and plateau regions. We also show that the thermal conductivity of as quenched La₇₀Cu₃₀ is typical of amorphous metals, contrary to information previously reported.     

Superconducting behavior of amorphous Zr70Cu30

Measurement of the Meissner penetration depth, λ(T) were made in amorphous Zr₇₀Cu₃₀ samples. The results indicate that this amorphous alloy behaves as a BCS superconductor with 2Δ(0)?kT_c = 3.8, where Δ(0) is the superconducting energy gap at T=0 and T_c the critical temperature. It is also concluded that the low energy excitation, TLS, characteristics of amorphous material does not contribute to T_c.     

Critical temperature and density of states in amorphous Zr70Cu30

By means of thermal heat treatment of amorphous Zr₇₀Cu₃₀ it is shown that the induced decrease in critical temperature is followed by a reduction in the electronic density of states of the same magnitude as that obtained by changing the Cu concentration. This result indicates that the density of states is the fundamental microscopic parameter determining the superconducting behavior.     

Electrical resistivity of amorphous Zr70Cu30 and the Kondo like model

Electrical resistivity measurements of amorphous Zr₇₀Cu₃₀ as a function of the concentrations of two level systems show that a Kondo like theory cannot explain the observed temperature dependence.     

Superconducting properties of amorphous sputtered Zr70Mo30

Specific heat, resistivity and critical superconducting fields (H_c and H_c2) measurements show that amorphous Zr₇₀Mo₃₀ is an intermediate superconductor (T_c = 4.3 K; λ = 0.77). The coupling strength is mainly governed by the electronic properties. Like in the Zr?3d alloys previously investigated, a discrepancy between the measured and calculated upper critical field slope is reported. The effect of two-level systems (TLS) needs to be clarified.     

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.     

用原位x射线小角散射研究块体非晶合金Zr55Cu30Al10 Ni5的结构弛豫

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     

利用Pr_(70)Cu_(30)晶界扩散改善烧结钕铁硼废料矫顽力的研究

钕铁硼磁体制备过程中出现的部分块体废料由于矫顽力较低,性能难以满足使用要求.本文主要通过晶界扩散技术来提高废料磁体的矫顽力.采用Pr_(70)Cu_(30)合金作为扩散介质,对烧结钕铁硼废料磁体进行了晶界扩散处理,研究了扩散温度、扩散时间和回火时间对扩散后的磁体性能的影响.结果显示,800℃下扩散3 h,磁体的矫顽力从原来的7.88 kOe(1 Oe=79.5775 A/m)提升至11.55 kOe,提升幅度为46.6%,同时剩磁没有明显降低.扩散后回火对矫顽力的提升有一定的作用.800℃下扩散4h后的磁体在500℃回火3h后,最高矫顽力可达11.97 kOe,比原磁体废料提高了51.9%,接近成品磁体的水平.显微组织分析证实了晶界扩散的作用.扩散处理后的磁体中,主相晶粒间形成了连续晶间相,起到有效的磁隔离作用,有利于矫顽力的提高.研究还发现,Pr_(70)Cu_(30)晶界扩散虽然可以使磁体腐蚀电位上升,但也会增加腐蚀电流密度,不利于磁体抗腐蚀性的改善.本文工作对于提高材料的成品率具有重要意义.     

Magnetic and structural properties of as-milled and heat-treated bcc-Fe70Cu30 alloy

A ferromagnetic solid solution with a nominal atomic composition Fe₇₀Cu₃₀ and a body-centered structure has been obtained by high-energy ball milling. The decomposition of the system is monitored by X-ray diffraction (XRD), magnetic measurements and Mössbauer spectroscopy. According to XRD, for healing temperatures below 723 K there is only a bcc phase in the material, while for heating temperatures above 723 K a new phase, with a fcc structure, appears, suggesting that the solid solution has decomposed into bcc-Fe and fcc-Cu. However, the magnetic behavior observed during the decomposition process indicates that this evolution is more complex than the simple decomposition into the equilibrium phases. This behavior can be summarized in two points: (1) a decrease in the magnetization at 5 K, and (2) drastic changes in the coercive field with the thermal treatment, soft magnetic behavior for the material in the as-milled state, superparamagnetism for low heating temperatures and a hardening of the material heated to above 723 K, for which the values of the coercive field at room temperature are several times higher than those for the as-milled sample. The Mössbauer spectroscopy performed at room temperature shows that for the heat-treated samples the Fe atoms are in two different phases: a ferromagnetic phase, which evolves to bcc-Fe, and a paramagnetic phase.     

On the structure of amorphous sputtered Zr76Cu24 alloy

X-ray diffraction experiments have been performed on amorphous sputtered Zr₇₆Cu₂₄ alloy in order to investigate the structural relaxation induced by thermal annealing below the crystallization temperature. Contrary to the low-temperature thermal properties which are very sensitive to heat treatments, only weak modifications affect the short-range structural order as defined by the total radial distribution function.     

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.     

Model relating superconductive penetration depth and metallurgical phase separation in amorphous La70Cu30

A model is proposed to account for the large increase in the measured penetration depth of superconducting, amorphous La₇₀Cu₃₀ when the specimens are annealed sufficiently long near, but below, the crystallization temperature. It is suggested that a metallurgical phase separation occurs with domain dimensions in the submicrometer range. Penetration depth measurements as a function of temperature in a weak magnetic field are a useful tool to detect changes in phase separation in high-K materials.     

Nuclear relaxation in normal and superconducting hydrogen alloys: Th4H15

T₁ measurements in the normal state show that the conduction electrons are responsible for the proton nuclear relaxation for T ? 300°K. an additional mechanism appears in the superconducting state.     

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.     

Physical aging in Zr46.75Ti8.25Cu7.5Ni10Be27.5 typical bulk metallic glass manifested as enthalpy relaxation

Enthalpy recovery is not only an important characteristic of physical aging of glass, but also a good tool to investigate the physical aging. Using differential scanning calorimeter (DSC), the enthalpy recovery of Zr_46.75Ti_8.25Cu_7.5Ni₁₀Be_27.5 bulk metallic glass (BMG) was studied. The typical characteristics of enthalpy recovery of glass including the sub-T _g peak and ‘overshot’ were found in BMG. The evolution of the sub-T _g peak and ‘overshot’ were described by the free volume theory and Hodge’s model, respectively. It was found that the former failed to describe the enthalpy recovery in the BMG, while the latter could give a qualitative explanation. In combination with the dynamics in the BMG, the origin of the enthalpy recovery in the BMG was discussed. The results show that BMGs are an ideal material to investigate the physical aging. The further understanding of physical aging of BMGs is useful to clarify the nature of glass and improve the application and device of new types of BMGs. Supported by the National Natural Science Foundation of China (Grant No. 50671118)     

高矫顽力的Co70Cu30合金纳米线阵列的制备及磁性研究

利用直流电化学沉积法, 在多孔阳极氧化铝模板中首次制备出了具有[220]取向的单晶 面心立方结构的CoCu固溶体合金纳米线阵列, 其Co含量高达70%.透射电子显微镜显示纳米线均匀连续, 具有较高的长径比, 约为300. 磁性测量表明所制备的Co₇₀Cu₃₀ 合金纳米线具有超高的矫顽力H_c//=2438 Oe(1 Oe=79.5775 A/m)和较高的矩形比S//=0.76, 远高于以往报道的CoCu合金纳米线的磁性, 分析表明磁性好的主要原因是由于较高Co含量和高形状各向异性. 通过磁性测量和模型计算, 得到Co₇₀Cu₃₀ 合金纳米线阵列在反磁化过程中遵从对称扇型转动的球链模型, 并从结构的角度分析了Co₇₀Cu₃₀合金纳米线阵列的反磁化行为.     

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.     

High thermal stability and low thermal conductivity in Ga30Sb70/Sb80Te20 nanocomposite multilayer films

The reliability characteristics and thermal conductivity of Ga₃₀Sb₇₀/Sb₈₀Te₂₀ nanocomposite multilayer films were investigated by isothermal resistance and transient thermoreflectance (TTR) measurements, respectively. The crystallization temperature and activation energy for the crystallization can be modulated by varying the layer thickness of Ga₃₀Sb₇₀. A data retention time of ten years of the amorphous state [Ga₃₀Sb₇₀ (3 nm)/Sb₈₀Te₂₀ (5 nm)]₁₃, [Ga₃₀Sb₇₀ (5 nm)/Sb₈₀Te₂₀ (5 nm)]₁₀, and [Ga₃₀Sb₇₀ (10 nm)/Sb₈₀Te₂₀ (5 nm)]₇ was estimated when ambient temperature is 137, 163, and 178 °C, respectively. Ga₃₀Sb₇₀/Sb₈₀Te₂₀ nanocomposite multilayer films were found to have lower thermal conductivity in both the amorphous and crystalline state compared to Ge₂Sb₂Te₅ film, which will promise lower programming power in the phase-change random access memory.     

Preparation and superconducting properties of YBa2Cu4O8

Samples of YBa₂Cu₄O₈ are prepared by means of a new high oxygen pressure technique employing oxygen-HIP. Both magnetization and resistivity measurements show the superconductivity transition at 82.5 K. The lower and upper critical fields of YBa₂Cu₄O₈ are obtained from the magnetization measurements. The Ginzburg-Landau parameters, ζ(0)=17 Å, λ(0)=2400 Å, are estimated from these results.     

退火诱导亚稳态Fe80Cu20合金固溶体的结构相变

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R_Cu—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Fe_８０Cu₂₀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="#">Fe_８０Cu₂₀合金 机械合金化