The microstructure development in arc-melt and melt-spun Fe50Ni10Cu20P10Si5B5 immiscible alloy

A six-component Fe₅₀Ni₁₀Cu₂₀P₁₀Si₅B₅ immiscible alloy was arc-melt in argon and it was melt-spun from various temperatures. The morphology and chemical composition of the cross-section of the ingot and melt-spun ribbons were analysed with a scanning electron microscope SEM/EDS. The melt-spun ribbon was investigated by a transmission electron microscope (TEM). The melting range of the alloy was investigated by means of differential thermal analysis (DTA) and for reference, the temperature change during free cooling of the alloy was controlled by pyrometer in the melt spinning device. The slow cooling rate resulted in the fractal surface structures formed by the Fe-rich regions and Cu-rich regions typical for the alloying system with a miscibility gap. The structures of the melt-spun ribbons were dependent on ejection temperatures before the melt spinning. The lower ejection temperatures resulted in the formation of the structures separated into Fe-rich and Cu-rich regions. This was due to rapid cooling within the miscibility gap. Ejection at higher temperatures led to the formation of a uniform amorphous/crystalline composite.     

Transformations in liquid state and microstructure development in immiscible Fe60Cu20P10Si5B5 alloy

A five-component Fe₆₀Cu₂₀P₁₀Si₅B₅ immiscible alloy was arc-melt and melt-spun from various temperatures. The microstructure and chemical composition of the ingot and melt-spun ribbons were analyzed using scanning electron microscope SEM/EDS. The melt-spun ribbon was investigated by transmission electron microscope (TEM). The melting range of the alloy was investigated by means of differential thermal analysis (DTA) and for reference, the temperature change during free cooling of the alloy was controlled by pyrometer in the melt spinning device. Processing with the slow cooling rate produced the fractal surface structures formed by the Fe-rich regions and Cu-rich regions. The arrangement of the regions was characteristic for the liquid immiscible alloys. It was found that the microstructures of the melt-spun ribbons depended on the ejection temperature. The lower ejection temperatures resulted in the formation of the lamellar structures separated into Fe-rich and Cu-rich regions. This was due to rapid cooling within the miscibility gap. Ejection at higher temperatures, above the miscibility gap led to the formation of a uniform amorphous/crystalline composite.     

Microstructural evolution of slowly solidified Cu-Ti-Zr-Ni amorphous alloy

The microstructures of slowly solidified Cu-Ti-Zr-Ni bulk amorphous alloy were identified by X-ray diffractometry (XRD) and transmission electron microscope (TEM). XRD and TEM examinations show that the deep eutectic structures of the tested alloy consist of CuTi₂-Cu₁₀Zr₇、Cu₃Ti-CuZr、Cu₃Ti-Cu₁₀Zr₇-CuZr low-order eutectics. Moreover, short-range ordering clusters in the melt with configuration similar to that of Cu₁₀Zr₇ compound may contribute to the glass forming ability of bulk amorphous Cu-Ti-Zr-Ni alloy.     

Intergrowth and stacking faults in the Sm5Co19 Phase

An electron microscope observation was made on the binary Sm-Co alloy. One-dimensional lattice images of Sm₅Co₁₉ taken with the incident beam parallel to the [010] and [110] directions of the hexagonal axis showed many stacking faults. The intergrowth with the Sm₂Co₇ phase was observed in the matrix of the Sm₅Co₁₉ phase, the analysis being based on the thickness of blockj layers estimated by the distance of lattice fringes.     

The effect of polyacrylamide on the crystallization of calcium carbonate: Synthesis of aragonite single-crystal nanorods and hollow vatarite hexagons

CaCO₃ nanorods were synthesized via a facile solution route by polymer-controlled crystallization in the presence of polyacrylamide (PAM). The morphology, size and crystal structure were characterized by means of scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray diffraction (XRD). The results suggest that the as-synthesized product was CaCO₃ (aragonite) nanorods with diameter ca. 50 nm and length ca. 1 μm. Selected area electron diffraction (SAED) pattern shows the single-crystal nature of CaCO₃ nanorods. The reaction time, temperature, pH and reactant concentration were systemically investigated. With the increase in the reaction time, hollow vaterite hexagonal disks can be obtained.     

Electrical resistivity evolution in the annealed amorphous Fe78Si9B13 ribbons

The electrical resistivity was measured at room temperature for the amorphous Fe₇₈Si₉B₁₃ ribbons annealed at various temperatures for different holding time. Although the annealed Fe₇₈Si₉B₁₃ ribbons are in full amorphous state, their electrical resistivity obviously varies with the annealing time. At every annealed temperature, the electrical resistivity evolution can be divided into regions I, II, and III, respectively. Using X-ray diffraction (XRD), scanning electron microscope (SEM), and differential scanning calorimetry (DSC), we investigated the ribbons overlapping regions I and II (called the focused ribbons, FRs). The results show that the change of electrical resistivity, fracture morphology, thermal effect in DSC analysis of the focused ribbons (FRs) can be ascribed to the evolution of the short range order (SRO) in the amorphous alloy.     

Crystallization kinetics of electro-deposited amorphous CoP alloys

The crystallization characteristics of amorphous Co-15.2 at.% P and Co-18.4 at.% P alloys were studied by means of a differential scanning calorimeter (DSC) and a transmission electron microscope (TEM). The analysis of DSC data obtained in the isothermal operation was performed by means of the Johnson-Mehl-Avrami (J-M-A) rate equation. The values of the J-M-A time index, n, for the crystallization of Co-15.2 at.% P and Co-18.4 at.% P alloys were 3.3 ± 0.1 and 2.2±0.1, respectively. It has been revealed through these experimental results and TEM observation during the crystallization process of the amorphous alloys that the crystallization of the former alloy results in interface-controlled three-dimensional spherical growth (n = 3) of Co₂P crystal, whereas the crystallization of the latter alloy results in two-dimensional growth (n = 2) of Co₂P disks having constant thickness. It has also been found that the apparent activation energy for the crystallization is 195 kJ/mol. and 190 kJ/mol. for Co-15.2 at.% P and Co-18.4 at.% P alloys, respectively.     

Phase transformation and crystallization kinetics of melt-spun Ni60Nb20Zr20 amorphous alloy

The glass transition and crystallization kinetics of melt-spun Ni₆₀Nb₂₀Zr₂₀ amorphous alloy ribbons have been studied under non-isothermal and isothermal conditions using differential scanning calorimetry (DSC). The dependence of glass transition and crystallization temperatures on heating rates was analyzed by Lasocka's relationship. The activation energies of crystallization, E_x, were determined to be 499.5 kJ/mol and 488.6 kJ/mol using the Kissinger and Ozawa equations, respectively. The Johnson–Mehl–Avrami equation has also been applied to the isothermal kinetics and the Avrami exponents are in the range of 1.92–2.47 indicating a diffusion-controlled three-dimensional growth mechanism. The activation energy obtained from the Arrhenius equation in the isothermal process was calculated to be E_x = 419.5 kJ/mol. The corresponding three dimensional (3D) time–temperature–transformation (TTT) diagram of crystallization for the alloy has been drawn which provides the information about transformation at a particular temperature. In addition, the intermetallic phases and morphology after thermal treatment have been identified by X-ray diffraction (XRD) and scanning electron microscope (SEM).     

Fabrication of cobalt ferrite nanostructures and comparison of their electrochemical properties

Cobalt Ferrite (CoFe₂O₄) nanorods and nanorings have been successfully controllable synthesized by solvothermal method. The specific characteristics were confirmed by X‐ray diffraction studies (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The measurement of their electrochemical properties as supercapacitor electrode materials indicate different morphological characterizations have various capacitive effects, and CoFe₂O₄ nanorings generally have larger specific capacitances than nanorods at different scan rates and current densities in 1.0 M KOH solution.     

Glass-formation and crystallization processes in Ag–Y–Cu alloys

Investigation of glass-formation and crystallization processes of several alloys of Ag–Y–Cu system was conducted. The samples were produced by melt spinning and Cu-mold casting. The structure of ribbon samples was examined by X-ray diffractometry and transmission electron microscopy. Phase transformations were studied by differential scanning and isothermal calorimetry and differential thermal analysis. Despite the large difference in atomic radii between the components in the investigated system, even being produced by melt spinning technique at high cooling rate, only Ag₆₁Y₂₉Cu₁₀ alloy with large supercooled liquid region was found to be X-ray amorphous. A principle for obtaining an alloy with high glass forming ability involving difference in atomic radii between the alloy components is considered. Efficient cluster packing model was also tested.     

Preparation of PbS nano‐microcrystals with different morphologies and their optical properties

PbS nano‐microcrystals were prepared from Pb(OAc)₂·3H₂O and sulfur in a solution without any surfactant using the solvothermal process. Different morphologies, mainly including polyhedron microcrystals and sphere‐like assemblies, were characterized using a scanning electron microscope (SEM) and a transmission electron microscope (TEM). PbS nano‐microcrystals with cubic crystal structure were detected using X‐ray diffraction (XRD), electron diffraction (ED) and high resolution transmission electron micrograph (HRTEM) techniques. The optical properties were investigated by ultraviolet‐visible (UV‐vis) spectroscopy, and photoluminescence spectroscopy (PL). The UV‐vis absorption peaks of PbS exhibited a large blue‐shift and the PL spectra had a strong and broad emission bands centered at 408 nm. The crystal growth mechanism of PbS was also discussed.     

Crystallization of amorphous Cu60Zr40 prepared by magnetron sputter deposition

The crystallization of amorphous Cu₆₀Zr₄₀ prepared by magnetron sputter deposition was studied by differential scanning calorimetry, X-ray diffraction and transmission electron microscopy. Calorimetric results were similar to those reported in the literature for liquid-quenched Cu₆₀Zr₄₀, including the manifestation of a glass transition. Crystallization above and below the glass transition temperature, T_g, occurred by nucleation and growth of the equilibrium phase, Cu₁₀Zr₇. This phase was characterized by convergent beam electron diffraction. With isothermal annealing below T_g, the time scale for crystallization indicated that the vapor-quenched alloy was kinetically more stable than the liquid-quenched alloy. This was interpreted as a difference in the quenched-in structures, produced by the different synthesis methods. During longer anneals, TEM analysis indicated that the structure was being contaminated by oxygen.     

Half opened microtubes of NaYF4:Yb,Er synthesized in reverse microemulsion under solvothermal condition

NaYF₄:Yb,Er micro/nanocrystals with different sizes and morphologies such as nanospheres, short flexural nanorods, and half opened microtubes, were synthesized in reverse microemulsion under solvothermal condition using the quaternary reverse microemulsion system, CTAB/1-butanol/cyclohexane/aqueous solution. The X-ray diffraction analysis confirmed that cubic phase NaYF₄:Yb,Er can completely transform to hexagonal phase with increasing reaction time. The scanning electron microscope and transmission electron microscope images revealed that the morphology of the product can be tailored by varying the reaction time. A possible crystalline growth process of the NaYF₄:Yb,Er micro/nanocrystals was discussed. The obtained half opened microtubes exhibited an intense green upconversion luminescence, which may be attractive in novel optoelectronic devices.     

<Emphasis Type="Italic">In situ</Emphasis> electron microscopy study of growth of WO<Subscript>3</Subscript> and MoO<Subscript>3</Subscript> nanowhiskers

WO₃ and MoO₃ nanowhiskers were grown from nanosize WO₃ and MoO₃ powders intensely irradiated with electrons in an electron microscope. Solid and hollow nanowhiskers of these materials were observed. A growth mechanism of nanowhiskers is suggested that is based on surface diffusion of WO₃ and MoO₃ molecules generated by the agglomerates of molecules under intense electron irradiation.     

Effect of SnSb Particle Size on Creep Behaviour under Power Law Regime of Sn-10%Sb Alloy

Sn-10 %Sb alloy was casted from the liquid state, drawn into wires of 0.55 mm in diameter or rolled into sheet of 0.2 mm thick. The as received as well as the heat treated specimens were examined by metallurgical microscope. Room temperature creep tests at constant loads were also carried out. The results obtained show that increasing annealing temperature, T_a, affects the structure and properties of the alloy. The increase of T_a leads to smaller SnSb particle size, therefore results in increasing its mechanical strength as measured by the decrease in steady state creep rate of specimen. The stress exponent parameter (m) calculated from the equation ϵ_S= A s_m was found to have higher values than usual and to decrease by increasing annealing temperature which was related to the associated decrease of the SnSb particle size.     

Structure and properties of nanocrystalline Cu70Fe18Co12 obtained by mechanical alloying

Cu₇₀Fe₁₈Co₁₂ alloy is prepared by mechanical alloying of pure Cu, Fe, Co powder using a high energy ball mill, with increasing milling time ranging from 4 to 8, 24, 36 and 54 h. The variation of the morphology and the elemental distribution were measured at these different stages on various grains of the alloy using a scanning electron microscope with a dispersive energy analyzer. Atomic clusters of iron were observed on some grains after 8 h of milling, confirming the non-homogenisation of the powder at this stage. Beyond 12 h, the homogenisation is ensured over a volume of one cube micron. Microstructural changes during the mechanical alloying have been studied by X-ray diffractometry (XRD) and Mössbauer spectroscopy. X-ray diffraction measurements confirm the dissolution of iron and cobalt phases in the FCC matrix of copper after 24 h of milling with increase of the structural parameter. This same dissolution was also measured by Mössbauer spectroscopy, confirming that after 4 h of milling the CuFe phase begins to form and iron dissolution is incomplete with partial amount of alpha Fe phase surviving after 36 h of milling.     

Microstructures of Mg–Zn–Nd alloy including small quasicrystalline grains

Two kinds of Mg-rich and low neodymium Mg–Zn–Nd alloys including icosahedral quasicrystal phase (I-phase) were prepared under conventional casting conditions. The microstructures and phases of Mg–Zn–Nd quasicrystal alloys were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and transmission electron microscopy (TEM). The results indicate that the I-phase in Mg–Zn–Nd quasicrystal alloy is a simple icosahedral quasicrystal with quasi-lattice of a_R = 0.525 nm. It has been proved that the as-cast Mg_70.8Zn₂₈Nd_1.2 quasicrystal alloy mainly consisted of I-phase and Mg₇Zn₃ matrix phase. While the as-cast Mg_70.5Zn_28.5Nd₁ alloy mainly consisted of I-phase, Mg₇Zn₃ matrix phase, dendrite α-Mg phase and a new rod-like hexagonal phase.     

Emissionselektronenmikroskopische Untersuchungen am Zweistoffsystem Niob-Eisen

Results from emission electron microscope investigations of thermal and mechanical behaviour of the Laves-phase NbFe₂ and of two-phase areas in the binary system Nb Fe are presented. The melting process of NbFe₂ samples with included μ-phase NbFe was observed in the emission microscope and supported the existence of a eutectic between both intermetallic compounds. The Laves-phase NbFe₂ was deformed plastically by a microhardness tester and also homogenously by a compressive device during electron microscope observations. Both yield stress and microhardness of NbFe₂ were measured as a function of temperature up to 1550 K. The relation between a critical temperature T₀ of the hardness-temperature curve and the melting temperature T_m was T₀/T_m = 0,64, in good agreement with results from other Laves-phases. During the heating of NbFe₂ samples a niobium oxide decoration structure appeared at residual air pressures from 1 · 10⁻⁶ torr to some 10⁻⁴ torr. The observed density of decoration points amounted to (1…5) · 10⁸ cm⁻². A discussion shows the possibility of a connection between decoration points and dislocations emerging from the crystal.     

A template‐free route for controlled synthesis of dumbbell‐like Sb2S3 microcrystals

Large amounts of dumbbell‐like Sb₂S₃ microcrystals were synthesized via a simple solvothermal treatment method. Various techniques such as x‐ray diffraction (XRD), field‐emission scanning electron microscope (FESEM), high‐resolution transmission electron microscope (HRTEM), selected area electron diffraction (SAED), and photoluminescence spectrometry (PL) have been used to characterize the obtained products. The results showed that the products belong to the orthorhombic Sb₂S₃ phase, and the dumbbell‐like Sb₂S₃ microcrystals were composed by uniform microrods. Besides, the morphologies of Sb₂S₃ microcrystals could be changed from microshperes to dumbbell‐like microcrystals by only adjusting the reaction solvent. The solvent effects are discussed in detail. Furthermore, the PL properties of the obtained Sb₂S₃ microcrystals clearly show shape effects. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hydrothermal synthesis and characterization of micro/nanostructured ZnSn(OH)6/ZnO composite architectures

Micro/nanostructured ZnSn(OH)₆/ZnO composite architectures were synthesized through a simple one‐step hydrothermal method. Phase structure and morphology of the products were characterized by using X‐ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). ZnSn(OH)₆ microcubes and ZnO nanorods with uniform size were interconnected to form the micro/nanostructured architectures. ZnO nanorods preferentially grow at edges and corners of the microcubes. Morphology of the products was susceptible to concentration of the reactants. With increasing reactant concentration, the ZnO nanorods grown on the surfaces of ZnSn(OH)₆ microcubes disappeared. Meanwhile, the smooth surfaces of the ZnSn(OH)₆ microcubes become coarsened and were etched to spherical outlines. Growth mechanism of the micro/nanostructured ZnSn(OH)₆/ZnO composite architectures was discussed and thermal decomposition properties of the micro/nanostructured ZnSn(OH)₆/ZnO composite architectures at high temperature were examined. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)