Characterization of ultrafine γ-Fe(C), α-Fe(C) and Fe3C particles synthesized by arc-discharge in methane

Ultrafine -Fe(C), -Fe(C) and Fe3C particles were prepared by arc-discharge synthesis in a methane atmosphere. The phases, morphology, structure and surface layer of the particles were studied by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) techniques and X-ray photoelectron spectroscopy (XPS). It was found that the mean particle size ranged from 9.8 to 12.8 nm. The surface of particles mostly consisted of a carbon layer and a little oxide. Phase transformation from -Fe(C) to -Fe(C) was studied by annealing in vacuum and by differential thermal analysis and thermogravimetry (DTA–TGA) measurement. The abundance of -Fe(C) was determined by a magnetization measurement to be approximately 30%. Phase transformation occurred between 300 and 500 °C in a flowing argon atmosphere. The Fe3C particles oxidized to -Fe2O3 and carbon dioxide at 610 °C or so. © 1998 Chapman & Hall     

The substrate problem in X-ray diffraction of boron-rich amorphous FeB alloys

Energy-dispersive X-ray diffraction spectra of boron-rich amorphous FeB alloys are presented. Special attention is paid to the preparation of the samples in a sputtering apparatus specially designed to give very pure materials. A solution is given to the “substrate problem”. The amorphous films are sputtered onto thin polycarbobate foils 2 μm thick fixed to a copper backing by means of SIRA adhesive wax. It is shown that the data evaluation is greatly simplified when the polycarbonate is directed towards the incident X-ray beam during the measurements.     

Mössbauer spectroscopic studies of the crystallization of amorphous Fe80B20−x Si x (x=0, 2, and 8) alloys

The crystallization process of amorphous Fe₈₀B_20–x Si _x (x=0, 2, and 8) ferromagnetic alloys has been studied by using ⁵⁷Fe Mössbauer spectroscopy and X-ray diffraction studies. Results for samples heat treated at different temperatures for different times show that the crystallization of Fe₈₀B_20–x Si _x samples having x=0 and 2 leads to -Fe and t-Fe₃B, while for x=8, it leads to -Fe, t-Fe₂B, and perhaps Fe-Si. It is further observed that the addition of silicon to the Fe-B system improves the thermal stability of the system.     

The effect of Fe on the crystallization behavior of Al–Mm–Ni–Fe amorphous alloys

The crystallization behavior and thermal stability of Al₈₆Mm₄Ni_10–x Fe _x alloys were investigated as a function of Fe content. Alloys, produced by a single roll melt-spinner at a circumferential speed of 52 m/s, revealed fully amorphous structures. The thermal stability of the present amorphous alloys increased with the increase of Fe content. The activation energy for crystallization of -Al increased as the Fe content increased. This increase of activation energy resulted in the simultaneous precipitation of -Al and intermetallic phase observed especially in Al₈₆Mm₄Ni₅Fe₅ and Al₈₆Mm₄Ni₂Fe₈ alloys. The glass transition was observed in DSC thermogram only after proper annealing treatment. The effect of alloy composition on the thermal stability could be explained in terms of the atomic structure of the amorphous alloy.     

Effect of illumination on the crystallization kinetics of amorphous Se80−xTe20Inx

The present paper reports the effect of illumination on the crystallization kinetics in amorphous Se_80–xTe₂₀In_x (0x10). The crystallization was monitored by measuring the electrical conductivity of isothermally annealed samples held at temperatures near the crystallization temperature. It is observed that the crystallization becomes faster in the presence of light as compared to a pure thermal case. There is no significant change in the activation energy under illuminated conditions as compared to the purely thermal case.     

Wetting of (0001) α-alumina single crystals by molten Mg–Al alloys in the presence of evaporation

The wetting of (0001) α-alumina single crystals by Mg–Al alloys over a wide composition range at 1073?K was investigated using an improved sessile drop method in a flowing argon atmosphere. The initial contact angles are between 103° and 84°, almost linearly decreasing with increasing nominal Mg concentration, suggesting that the addition of Mg to Al improves the initial wettability. According to the evolution of contact angle and contact diameter, representative stages were identified to characterize the complex wetting behavior in the presence of evaporation. The wetting kinetics was dependent on the nominal Mg concentration in the alloy. Two patterns of “stick–slip” behavior were observed in the wetting process and interpreted by combining the effects of interfacial reaction and evaporation of magnesium. In addition, the dependence of the interfacial reaction on the Mg–Al alloy concentration was thermodynamically analyzed. The dominant reaction product at 1073?K should be MgO when x _Mg?>?9?mol%, while MgAl₂O₄ when x _Mg?<?9?mol%. However, because of the continuous consumption of Mg due to the evaporation and reaction, its concentration in the alloy progressively decreased with time. As a result, MgO formed usually earlier while MgAl₂O₄ later even for the alloys with higher than 9?mol% Mg.     

Crystallization process and magnetic properties of Fe100−x,B x (10 ≦ × ≦ 35) amorphous alloys and supersaturated state of boron inα-Fe

Amorphous specimens of Fe_100–x B _x were prepared in the range 10 × 35 at % B by a single-roller method. The crystallization process and the boron concentration dependence of the Curie temperature were examined by differential scanning calorimetry, X-ray diffraction, Mössbauer spectroscopy and magnetic measurements. Two-step crystallization was observed in specimens with× < 17: amorphous amorphous + boron-supersaturated b c c phase (-Fe(B)) t-Fe₃B +-Fe. A single-Fe(B) phase was not observed. The transition temperature from t-Fe₃B to stable (-Fe + t-Fe₂B) sensitively depends on the boron content in the alloys. The crystallization temperature (T _x) of the amorphous alloys was almost unchanged for 17 × 31, but increased remarkably at high boron concentrations of× 33, where the decomposition products consisted of t-Fe₂B and o-FeB. The Curie temperature (T _c) of the amorphous phase was as low as 480 K at× = 10, increased with increasing boron content up to 820 K and then decreased in the high boron concentration alloys of× > 28. A single-Fe(B) phase was not detected in the as-quenched specimens of× = 8 and 10. The phase coexisted with the o-Fe₃B and amorphous phases. The lattice parameter of the phase was 0.2861₀ nm which was smaller than that of pure iron by 2/1000, indicating the substitutional occupation of boron atoms in the b c c lattice.     

Photoconductivity in single crystals of (TlGaSe2)1−x(TlInS2)x alloys (0−0.45 ≤ x ≤0.55-1)

The spectral distribution of the photoconductivity in (TlGaSe₂)_1−x(TlInS₂)_x single crystals has been studied at 77 K and 300 K. At O ≤ x ≤ 4, Eg is observed to vary linearly with x. Eg(x) deviates from linearity at x = 0.6. This deviation is attributed to the effect of disorder in the composition. Over the range 0.6 to 2.2 eV pronounced impurity photoconductivity is detected at 77 K and 300 K. Deep impurity levels and their neighbourhood in this alloy are established to preserve their positions with the variation in the composition. The analysis of the obtained results indicates that the impurity centres are mainly connected with the cation neighbourhood.     

Formation and properties of amorphous (Fe1−x Nb x ) l B100−l

Amorphous (Fe_1–x Nb _{x l} B_100–l alloys with 0 x 0.15 and 74 T _g, crystallization temperatureT _x, and microhardnessH _v, but to decrease the magnetization and Curie temperatureT _c. The effects of niobium onT _x,H _v, andT _c in iron-based amorphous alloys are similar to those of chromium, manganese, molybdenum, tungsten and vanadium.     

The impact of hydrogen on the ductility loss of bainitic Fe–C alloys

The influence of hydrogen on the mechanical properties of generic lab-cast Fe–C bainitic alloys is studied by tensile tests on notched samples. The bainitic microstructure is induced in a 0.2% C and 0.4% C Fe–C alloy by an appropriate heat treatment. The hydrogen embrittlement susceptibility is evaluated by mechanical tests on both in situ hydrogen pre-charged and uncharged specimens. The observed ductility loss of the materials is correlated with the present amount of hydrogen and the hydrogen diffusion coefficient. In addition to the correlation between the amount of hydrogen and the hydrogen-induced ductility loss, the hydrogen diffusion during the tensile test, quantified by the hydrogen diffusion distance during the test, appears to be of major importance as well.     

Non-equilibrium crystallization diagram for the Co75.26−xFe4.74(BSi)20+x amorphous metal alloys

A non-equilibrium crystallization diagram for Co sub-surface layers of the Co_75.26–x Fe_4.74(BSi)_20+x amorphous alloy for x > 1 during magnetic field annealing is determined using Transmission Electron Microscopy (TEM). The diagram shows that, depending on the composition and temperature, the Co sub-layer exhibits five distinctively different microstructures when the metallic glass is heat treated below its bulk crystallization temperature. At high boron content, the structure is dominated by the FCC structure with a high degree of oxygen impurity faulting regardless of the annealing temperature. At low concentration, the Co sub-layer exhibits FCC or HCP structures, depending on the temperature. Also found was a two-phase region in which FCC and HCP Co co-existed. Such a diagram serves as a useful guide to obtaining the desired properties as the microstructure is closely linked to the magnetic properties of the material.     

The change of the electric conductivity type in crystals of Bi2−xInxTe3 solid solutions

Room-temperature values of the Hall constantR _H (Bc), Seebeck coefficient (Tc), and the temperature dependence of the electric conductivity _c in the 120–360 K temperature interval have been investigated on samples of Bi_2–x In _x Te₃ crystals prepared by the Bridgman technique. It has been established on the basis of the changes of these transport coefficients with increasing content of indium that for values close tox=0.1 the conductivity type changes from p-type to n-type. Suppression of the concentration of holes due to the incorporation of In atoms into the crystal lattice of p-Bi₂Te₃ is accounted for by a model of point defects in the Bi₂–xIn _x Te₃ crystal lattice. It is assumed that the arising uncharged substitutional In _Bi ^x defects polarize the Bi₂Te₃ lattice and thus lower the concentration of anti-site defects Bi_Te, whose charges are compensated by holes. The dominant defects in the crystal lattice of n-Bi_2–x In _x Te₃ are the tellurium vacancies V _Te ^. .     

Precipitation of (PdxAg1−x)3 In in Ag-25% Pd-In alloys and the partial phase diagram of ternary Ag-Pd-In alloys

A study was carried out to determine the partial phase diagram for the system Ag-25 wt % Pd–y wt% In with y 8 by X-ray powder diffraction and differential thermal analysis. The liquidus and solidus temperatures decreased with increasing indium content up to 8 wt % In for a given 25 wt % Pd. The solvus curve of phase identified as Pd_xAg_1-x)₃ In was determined by the parametric method and the temperature dependence of In-solubility in Ag-25 wt % Pd was very strong above 900 °C. ©2000 Kluwer Academic Publishers     

The morphology of α′ martensite in a two-phase (α+γ) Fe-Cr-Ni stainless steel

Both lath-shaped and martensites are induced by tensile deformation within of a two-phase ( + ) Fe-Cr-Ni stainless steel, forms from the through the at an intersection of two crystals. These are observed both when is surrounded by and when borders . The amount of strain at which both and nucleate, increases with test temperatures in the range –196 to 50° C. Adjacent laths are either twin-related, or 5, 9, 15 or 19° off the twin relationship, as found by analysing electron diffraction patterns.     

Investigation of magnetic properties of Fe61Co8Zr4−xY2+xNi5Nb5B15 amorphous alloys (x = 0, 1) in the form of ribbons

Amorphous Fe₆₁Co₁₀Zr_4?xY_2+xNb₅B₁₅ (x = 0, 1) samples in the form of a ribbon with a thickness of approximately 30 μm and a width of about 4 mm have been investigated. The ribbons were obtained by a single roller melt-spinning method with the wheel linear velocity equal to 35 m/s. Microstructural studies, using X-ray spectroscopy, confirmed that samples in the as-quenched state were fully amorphous. Measurements carried out using a vibrating sample magnetometer allowed values of coercivity and saturation magnetization to be obtained. On the basis of performed measurements, it can be stated that Fe₆₁Co₈Zr₄Y₂Ni₅Nb₅B₁₅ alloy exhibits superior soft magnetic properties compared with the Fe₆₁Co₈Zr₃Y₃Ni₅Nb₅B₁₅ alloy. The former alloy possesses: a higher value of saturation magnetization, almost double the value of magnetic permeability, approximately half the value of coercivity and substantially smaller core losses than the latter alloy.     

Mechanisms of the temperature quenching of luminescence due to deep centres in CdSexTe1−x (0 < × < 1) alloys

In CdSe_xTe_1−x (0 < x < 1) sintered films, both the dependence of the luminescence intensities of the bands with λ_m=0.92 μm and 1.16 μm at 77 K for x=1 on temperature and the dependence of band intensities on the excitation level measured at low temperatures and from the ranges of band quenching are investigated. The data obtained enable conclusions to be drawn about the tw0 band quenching mechanisms: the “external” mechanism is valid for the 0.92 μm bands and the “internal” mechanism is valid for the 1.16 μm bands, with the exception that CdSe_0.3Te_0.7 exhibits the external mechanism. A discontinuous change in the surroundings of the emission centres from selenium atoms to tellurium atoms has been found to take place for this alloy composition.     

The design and properties of pseudobinary alloys (PbTe)1−x–(SnTe)x with gradient composition

The pseudobinary thermoelectric alloys (PbTe)_1−x–(SnTe)_x (0≤x≤0.4) doped with 0.02 mol% Ag concentration were prepared by pressureless sintering (PS), and their properties were optimized to fit the preparation of functionally graded materials (FGM) with gradient composition. The calculation shows that the FGM can raise the maximal power output to approximately 200.0 (W m⁻²), at least 21% greater than that of the best monolithic alloys (PbTe)_0.6–(SnTe)_0.4. The measurement shows that the maximum power output of FGM is about 175.0 (W m⁻²), and at least increases by about 16% as compared to those of any monolithic materials (PbTe)_1−x–(SnTe)_x (0≤x≤0.4) without or with different Ag concentration doping.