Dendritic growth and solute trapping in rapidly solidified Cu-based alloys

Rapid solidification of binary Cu-22%Sn peritectic alloys and Cu-5%Sn-5%Ni-5%Ag quaternary alloys was accomplished by glass fluxing, drop tube and melt spinning methods. The undercooled, by glass fluxing method, Cu-22%Sn peritectic alloy was composed of α(Cu) and δ(Cu41Sn11) phases. If rapidly solidified in a drop tube, the alloy phase constitution changed from α(Cu) and δ(Cu41Sn11) phases into a single supersaturated (Cu) phase with the reducing of droplet diameter, and the maximum solubility of Sn in (Cu)...     

Pd40.5Ni40.5P19合金的无容器凝固及其大块金属玻璃的形成

熔态Pd_40.5Ni_40.5P₁₉,合金在1.2落管中被分散成液滴,并在自由下落过程中凝固.由于实验是在纯净的氦气氛下的无容器环境中进行,因而消除了由于表面氧化层的存在以及由于液态合金与容器壁的接触所造成的非均匀成核,得到了迄今尺寸最大的直径2mm的规则金属玻璃球体. 关键词：     

Structural Feature and Solute Trapping of Rapidly Grown Ni3Sn Intermetallic Compound

The rapid dendritic growth of primary Ni3Sn phase in undercooled Ni-30.9%Sn-5%Ge alloy is investigated by using the glass fluxing technique. The dendritic growth velocity of Ni3Sn compound is measured as a function of undercooling, and a velocity of 2.47m/s is achieved at the maximum undercooling of 251 K （0.17TL）. The addition of the Ge element reduces its growth velocity as compared with the binary Ni75Sn25 alloy. During rapid solidification, the Ni3Sn compound behaves like a normal solid solution and it displays a morphological transition of ＂coarse dendrite-equiaxed grain-vermicular structure＂ with the increase of undereooling. Significant solute trapping of Ge atoms occurs in the whole undercooling range.     

无容器过程中Pd-Ni-P系合金的过冷及金属玻璃形成

在1.2m落管中对Pd_43.5Ni_43.5P₁₃和Pd₄₀Ni₄₀P₂₀合金进行了无容器过冷实验。通过在落管中充以不同的惰性气体,从而调节过冷液滴的散热条件,研究了冷却速率对于Pd₄₀Ni₄₀P₂₀合金的玻璃形成、晶体成核和长大的影响。确定了在落管中形成玻璃的临界冷却速率。此外,液滴下落以前的初始温度也与玻璃形 关键词：     

Short range order in (Ni65Fe35)77B23 metallic glass by neutron diffraction

The S(Q) structure factor of (Ni₆₅Fe₃₅)₇₇B₂₃ metallic glass was measured by time-of-flight neutron diffraction up to 24 Å^?1 momentum transfer. The distribution of transition metal-boron and transition metal-transition metal first neighbour atom pairs is resolved in the distribution function obtained from S(Q) by Fourier transformation. The distances of these first neighbours pairs, the width of their distribution, the partial coordination numbers and the short range order parameter are given. The results on (Ni₆₅Fe₃₅)₇₇B₂₃ and on the previously studies Fe₈₁B₁₉ amorphous alloys are compared.     

Metastable phase separation and rapid solidification of undercooled Co-Cu alloy under different conditions

The metastable liquid phase separation and rapid solidification behaviours of Co_61.8Cu_38.2 alloy were investigated by using differential thermal analysis (DTA) in combination with glass fluxing, electromagnetic levitation (EML) and drop tube techniques. It is found that the liquid phase separation process and the solidification microstructures intensively depend on the experimental processing parameters, such as undercooling level, cooling rate, gravity level, liquid surface tension and the wetting state of crucible. Large undercooling and surface tension difference of the two liquids tend to facilitate further separation and cause severe macrosegregation. On the other hand, rapid cooling and low gravity effectively suppress the coalescence of the minority phase. Severe macrosegregation patterns are formed in the bulk samples processed by both DTA and EML. In contrast, disperse structures with fine spherical Cu-rich spheres homogeneously distributed in the matrix of Co-rich phase have been obtained in drop tube.     

Dendrite growth characteristics within liquid Fe-Sb alloy

Bulk samples and small droplets of liquid Fe-10%Sb alloys are undercooled up to 429 K (0.24TL) and 568 K (0.32TL), respectively, with glass fluxing and free fall techniques. The high undercooling does not change the phase constitution, and only the αFe solid solution is found in the rapidly solidified alloy. The experimental results show that when the undercooling is below 296 K, the growth velocity of αFe dendrite rises exponentially with the increase of undercooling and reaches a maximum value 1.38 m/s. S...     

Pd-Ni-P大块金属玻璃的形成及其转变动力学

本文报道了Pd-Ni-P合金的过冷实验结果,研究了冷却速度对合金过冷行为的影响。通过将样品包裹在B₂O₃中从而减少样品的表面非均匀生核,使得样品在极低的冷却速度下形成大块金属玻璃。在玻璃转变温度(T_g=590K)处,冷却速度低达1K/s。利用经典的均匀生核与非均匀生核理论,计算了Pd₄₀Ni₄₀P₂₀合金的温度、时间转变曲线(即TTT图)。确定了合金的临界冷却速度。对结果进行了详细的讨论。 关键词：     

落管中Al4Mn合金的形核研究

用1.2米长的落管对Al₄Mn合金进行了形核与过冷的研究.在落管底部收集到的样品中得到了正交Al₆Mn,β-Mn,两个十次准晶相关相、一个二十面体五次准晶相关相和十次准晶畴.发现这些相的含量与样品的尺寸大小有关,根据传统的形核理论对相含量与样品尺寸大小之间的关系作了定性的分析和讨论. 关键词：     

Measurement and simulation of specific heat for metastable liquid Ni80Fe10Cu10 alloy

The specific heat of undercooled liquid Ni₈₀Fe₁₀Cu₁₀ alloy was experimentally measured by electromagnetic levitation drop calorimeter, and also numerically simulated by the molecular dynamics method. The achieved maximum undercooling is up to 252 K (0.15 T _L) in the experiments, and the measured result is 41.67 J mol⁻¹ K⁻¹. The simulation provides calculated data within 0∼702 K undercooling range, which is much broader than the experimental regime. The simulated value is 37.02 J mol⁻¹ K⁻¹. Although there exists a difference of 4.65 J mol⁻¹ K⁻¹ between them, the result is quite acceptable for simulation. Furthermore, the liquid structure of undercooled Ni₈₀Fe₁₀Cu₁₀ alloy is studied in terms of the total and partial pair distribution functions, which display that the ordered degree of atoms enhances from a normal liquid to metastable state.     

Torque magnetometer measurements of the temperature dependence of induced anisotropy energy and of saturation magnetization in amorphous Fe40Ni40P14B6

Induced anisotropy energy K_u and saturation magnetization M have been measured as a function of temperature T between 77 K and T_c on co$\text{n}$venient specimens of amorphous Fe₄₀Ni₄₀P₁₄B₆ by means of a torque magnetometer. The M vs. T curve is found to follow an anomalously low behaviour with respect to crystalline materials. The exper$\text{i}$mental K_u vs. T curve is well fitted by a M² law, also different from higher power laws typical of crystalline alloys.     

Hyperfine interactions, structure and magnetic properties of nanocrystalline Co–Fe–Ni alloys prepared by mechanical alloying

Mechanical alloying method was used to prepare nanocrystalline Co₅₀Fe₄₀Ni₁₀, Co₅₂Fe₂₆Ni₂₂ and Co₆₅Fe₂₃Ni₁₂ alloys. X-ray diffraction proved that during milling Co–Fe-based solid solution with b.c.c. lattice was formed in the case of Co₅₀Fe₄₀Ni₁₀, while for Co₅₂Fe₂₆Ni₂₂ and Co₆₅Fe₂₃Ni₁₂ compositions Co–Ni-based solid solutions with f.c.c. lattice were obtained. Mössbauer spectroscopy revealed similar values of the average hyperfine magnetic fields for all alloys, e.g. 32.17, 32.24 and 31.21 T for Co₅₀Fe₄₀Ni₁₀, Co₅₂Fe₂₆Ni₂₂ and Co₆₅Fe₂₃Ni₁₂ alloys, respectively. Magnetization measurements allowed to determine the effective magnetic moment, Curie temperature, saturation magnetization and coercive field for the obtained alloys.     

Formation of NI80P20 solid solution phase under pressure

A Ni-P solid solution phase was obtained by quenching of melts under a pressure of 4.5 GPa. This was considered as a metastable high pressure phase. Despite the lack of thermodynamic parameters for Ni₈₀, P₂₀ alloy under pressure, the degree of undercooling, nucleation frequency and crystal growth velocity were calculated. We conclude that metastable phases with the same composition as the melting phase, such as supersaturated solid solution phase and amorphous phase, are easily prepared by high-pressure quenching.     

A comparative study of the structure and crystallization of bulk metallic amorphous rod Pr60Ni30Al10 and melt-spun metallic amorphous ribbon Al87Ni10Pr3

Pr-based bulk metallic amorphous （BMA） rods （Pr60Ni30Al10） and Al-based amorphous ribbons （Al87Ni10Pr3） have been prepared by using copper mould casting and single roller melt-spun techniques, respectively. Thermal parameters deduced from differential scanning calorimeter （DSC） indicate that the glass-forming ability （GFA） of Pr60Ni30Al10 BMA rod is far higher than that of Al87Ni10Pr3 ribbon. A comparative study about the differences in structure between the two kinds of glass-forming alloys, superheated viscosity and crystallization are also made. Compared with the amorphous alloy Al87Ni10Pr3, the BMA alloy Pr60Ni30Al10 shows high thermal stability and large viscosity, small diffusivity at the same superheated temperatures. The results of x-Ray diffraction （XRD） and transmission electron microscope （TEM） show the pronounced difference in structure between the two amorphous alloys. Together with crystallization results, the main structure compositions of the amorphous samples are confirmed. It seems that the higher the GFA, the more topological type clusters in the Pr-Ni-Al amorphous alloys, the GFAs of the present glass-forming alloys are closely related to their structures.     

Grain boundaries in the refined solidification structure of undercooled Ni75Pd25

When a single-phase alloy solidifies in a low-undercooling range or above a critical undercooling, grain-refined structures are obtained. Taking Ni₇₅Pd₂₅ alloy as an example, the microscopic orientation of the refined grains was investigated by electron backscattered diffraction technology. It is revealed that the refined grains at low undercooling are completely randomly distributed. In the refined structure at high undercooling, certain grain boundaries with misorientation angles less than 5° can be observed, while most of the grain boundaries have large misorientation angles. The inverse pole figure indicates that the refined grains at high undercooling have a textured crystallographic orientation. The fact that twins exist in the refined structure at high undercooling and the dendritic substructure arms exhibit no misorientation supports such an argument that the grain refinement at high undercooling results from the recrystallization of the solidification dendrites.     

Ce2-xDyxFe17合金的磁熵研究

研究了Ce_2-xDy_xFe₁₇(x=0.0,0.3,0.5,1.0)系列合金在77—298K温区范围磁熵变,发现Ce_2-xDy_xFe₁₇系列合金有较大的磁熵变,居里温度可通过离子替代而改变,是一种可供选择的室温磁致冷材料.     

Si掺杂的铁磁形状记忆合金Co50Ni21Ga29Six的物性研究

成功生长了Co₅₀Ni₂₁Ga₂₉:Si(x=1,2)单晶样品,对其磁性,马氏体相变及其相关性质进行了细致的测量.发现掺Si成分的单晶具有非常迅速的马氏体相变行为、2.5％的大相变应变、大于100 ppm的磁感生应变和4.5％的相变电阻.进一步研究指出,在CoNiGa合金中掺入适量Si元素,能够降低材料的马氏体相变温度,减小相变热滞后,提高材料的居里温度,并使得磁性原子的磁矩有所降低.尤其重要的是Si元素的添加能够增大材料马氏体的磁晶各向异性能,改善马氏体变体的迁移特性,从而获得更大的磁感生应变. 关键词： 铁磁形状记忆合金 Heusler合金 50Ni₂₁Ga₂₉Si_x')" href="#">Co₅₀Ni₂₁Ga₂₉Si_x     

Low temperature resistivities of FexNi80-xP14B6 metallic glasses

The resistivities of six Fe_xNi_80-xP₁₄B₆ alloys have been measured between 1.5 and 50 K. It is found that the resistivity variations both below and above the resistivity minima depend on the transition metal composition. The room temperature coefficients of the resistivity indicate the existence of the magnetic contribution to the resistivity.     

Magnetic properties on shape memory alloys Ni2Mn1+xIn1−x

X-ray powder diffraction and magnetization measurements were done on the magnetic shape memory alloys Ni₂Mn_1+xIn_1−x. On the basis of the results, the magnetic phase diagram was determined for Ni₂Mn_1+xIn_1−x alloys. Magnetization measurements make clear that the excess Mn atoms, which substitute for In sites, are coupled ferromagnetically to the ferromagnetic manganese sublattices. A magnetic phase diagram of Ni₂Mn_1+xIn_1−x alloys is discussed qualitatively on the basis of the interatomic dependence of the exchange interactions.