Improved tensile ductility of amorphous Fe78Si9B13 alloy using electrodeposited nano-Ni layers

In order to improve the tensile ductility of amorphous Fe₇₈Si₉B₁₃ alloy, nano-Ni layers were electrodeposited on the amorphous alloy ribbon and amorphous Fe₇₈Si₉B₁₃/nano-Ni laminated composite was prepared. The tensile ductility of laminated composite and monolithic amorphous alloy at both room and high temperatures was examined. The elongation of the amorphous Fe₇₈Si₉B₁₃ alloy and that in the laminated composite increases from 1.4% to 8.5% and from 36.3% to 115.5% at room temperature and 450 °C, respectively. The improved tensile ductility using electrodeposited nano-Ni layers is attributed to a good bonding between the amorphous Fe₇₈Si₉B₁₃ layer and nano-Ni layers. The amorphous layer can deform in conformity with Ni layers and be significantly stretched without fracture.     

Structure and magnetic properties of bulk amorphous Fe60Co10Ni10Zr7B13 alloy formed by mechanical synthesis and hot pressing

Formation and magnetic properties of the bulk amorphous Fe₆₀Co₁₀Ni₁₀Zr₇B₁₃ alloy are described. The amorphous powder was prepared by high-energy ball milling of the amorphous ribbon and then was pressed under high pressure and temperature to obtain a bulk alloy in the form of a disc 5 mm in diameter and 2.5 mm thick. The compacted discs are fully amorphous as confirmed by X-ray diffraction and Mössbauer spectroscopy measurements. Differential scanning calorimetry curve recorded for the amorphous ribbon shows two exothermal peaks related to two stages of crystallization. Similar thermal behavior is observed for the powder samples. Hysteresis loops obtained for the amorphous ribbon, as-milled and compacted powders reveal their soft magnetic properties.     

The short-range order in ternary ZrF4---BaF2---ErF3 glasses

The short-range order structures in ternary ZrF₄---BaF₂---ErF₃ glasses have been studied by X-ray absorption fine structure (XAFS). The near-neighbor structures around Zr, Ba and Er have been determined and compared with that in binary ZrF₄---BaF₂ glasses. The near-neighbor structures around Zr and Ba are scarcely affected by doping with ErF₃. The structural parameters of near neighbors around Er in the glasses are near to that in ErF₃, but the corresponding distance and coordination number of near neighbors in the glasses decrease slightly. It is also observed that the intensities of the white lines at the Er L and L absorption edges in these glasses are different from that in c-ErF₃. Meanwhile, compared with that of the corresponding fluoride, the changes of the ‘white line’ at the Er L_,-edges in the glasses differ from the case of Nd. The causes leading to these differences are discussed.     

Internal friction and shear modulus of certain metallic glasses

We have measured the temperature dependence of the internal friction and shear modulus of metallic glass alloys Fe₄₀Ni₄₀P₁₄B₆, Fe₂₉Ni₄₉P₁₄B₆Si₂, Fe₈₀B₂₀ and Fe₇₈Mo₂B₂₀ in the glassy and crystalline phases using a torsional pendulum technique. The internal friction in the glassy phase remains approximately constant from room temperature to a temperature which depends on the annealing treatment, and the rises exponentially with temperature. The internal friction measurements were made at two different frequencies (0.2 Hz and 1.0 Hz) and the activation energies for the relaxation processes estimated by the frequency shift method. The shear modulus increases by about 30% when the amorphous alloys are crystallized. The amorphous alloys Fe₈₀B₂₀ and Fe₇₈Mo₂B₂₀ exhibit Invar type behaviour which disappears upon crystallization.     

Preparation and characterization of Ni-incorporated FeS2 single crystals

Nickel-incorporated FeS₂ single crystals with various Ni compositions of Fe_0.99S₂:Ni_0.01, Fe_0.98S₂:Ni_0.02, Fe_0.96S₂:Ni_0.04, and Fe_0.9S₂:Ni_0.1 were grown by chemical vapor transport (CVT) method using ICl₃ as a transport agent. Physical properties of the Ni-incorporated FeS₂ single crystals were characterized using X-ray diffraction, Raman spectroscopy, electrical conductivity, and photoconductivity (PC) measurements. By means of the analyses of the X-ray diffraction patterns, the whole series of Ni-doped FeS₂ single crystals were determined to be single-phase and isostructural. Raman spectroscopy of the Ni-doped FeS₂ crystals was carried out at room temperature. Raman resonant peaks of the Ni-doped FeS₂ crystals demonstrate an energy red-shift behavior with respect to the increase of the dopant densities. Conductivity measurements show the resistivity of the Ni-doped FeS₂ decreased as the doping concentration of Ni is increased. Nickel is an n-type dopant, which behaves like a donor level existed near the conduction band edge of the synthetic FeS₂. On the other hand, dopant effect of nickel on the synthetic FeS₂ also destroys the photoconductive sensitivity in the photoconductivity measurements.     

RDF analysis of structural evolution during the primary crystallization of the Fe40Ni38Mo4B18 glassy alloy

The changes in the atomic structure of amorphous Fe₄₀Ni₃₈Mo₄B₁₈ during the crystallization process were studied by X-ray diffraction. The radial distribution functions of various specimens frozen at significant points of the relative DSC thermograms, were obtained from the interference functions by means of the usual Fourier analysis.

It appears from the results that the onset of crystal formation implies the simultaneous occurrence of atomic rearrangements involving the basic structural units already present in the unannealed sample; a five-fold symmetry and icosahedral structure were found for these units. An effort was made to correlate the progress in the crystalline organization with the significant features of the DSC related thermograms.     

Al2O3-TiO2 and Al2TiO5 ceramic materials by the sol-gel process

Ceramic materials with a very low thermal expansion coefficient are synthesized by the sol-gel process. The binary gel is obtained by hydrolysis and polycondensation reactions of organometallic compounds of aluminium and titanium. The thermal evolution of the amorphous powder is followed by DTA and TGA measurements. Structural evolution is followed using X-ray diffraction. The crystallization of the TiO₂ rutile and Al₂O₃ corindon starts at 700 and 900°C respectively. The transformation of Al₂O₃ and TiO₂ into Al₂TiO₅ appears between 1200 and 1300°C. The densification of the powder is performed by the hot pressing process. The shrinkage of the powder was previously followed by dilatometric measurements. The physical properties of the final material are studied as a function of pressing parameters.     

Mössbauer and X-ray studies of the kinetics of crystallization in glassy Fe---B alloys

X-ray crystallography and Mössbauer spectroscopy were used to investigate the crystallization of the amorphous Fe_100−xB_x alloys, 14 x 20 annealed at 615 K. As a result of the heat treatment, the formation of crystalline -Fe and Fe₃B were observed. Variations in the values of the isomer shift and the orientation of the axis of magnetization indicate changes in the iron-boron bonding and the local atomic arrangement.

Formation of the -Fe phase was determined as a function of boron concentration and annealing time. Crystallization rates of that phase were observed to be dependent on boron concentration and on the annealing time. The average hyperfine field of the untreated samples was observed to increase till x = 17 after which it decreased. This is explained in terms of the Invar behavior of Fe₈₃B₁₇. The anomalous crystallization of Fe₈₆B₁₄ is proposed to be due to the existence of interstitial-like boron sites in a near bcc short range atomic structure.     

Study of electrical properties of MoO3–Fe2O3–P2O5 and SrO–Fe2O3–P2O5 glasses by impedance spectroscopy. II

The electrical and dielectric properties for three series of MoO₃–Fe₂O₃–P₂O₅ and one series of SrO–Fe₂O₃–P₂O₅ glasses were measured by impedance spectroscopy in the frequency range from 0.01 Hz to 3 MHz and over the temperature range from 303 to 473 K. It was shown in Part I that the MoO₃ is incorporated into phosphate network and the structure/properties are strongly influenced by the overall O/P ratio. The Fe₂O₃ content and Fe(II)/Fe_tot ratio in these glasses have significant effects on the electrical conductivity and dielectric permittivity. With decreasing Fe₂O₃ content in MoO₃–Fe₂O₃–P₂O₅ glasses with O/P at 3.5 the dc conductivity, σ_dc(ω) decreases for two orders of magnitude, which indicates that the conductivity for these glasses depends on Fe₂O₃ and is independent of the MoO₃ content. Also, the dielectric properties such as ^′(ω), ^″(ω) and σ_ac(ω) and their variation with frequency and temperature indicates a decrease in relaxation intensity with increase in the concentration of MoO₃. On the other hand, the dc conductivity for MoO₃–Fe₂O₃–P₂O₅ glasses with O/P > 3.5 increases with the substitution of MoO₃ which has been explained by an increase in the number of non-bridging oxygens and formation of Fe–O–P bonds that are responsible for formation of small polarons. The increase in the dielectric permittivity, ^′(ω) with increasing MoO₃ content is attributed to the increase in the deformation of glass network with increasing bonding defects. For SrO–Fe₂O₃–P₂O₅ glasses the conductivity and dielectric permittivity remained constant with increasing SrO.     

Elastic constant anomaly in Fe80−xMoxB20 metallic glasses

The extensional sound velocities V_E of Fe_80−xMo_xB₂₀(x = 6, 7, 8) metallic glasses have been measured between 100 and 600 K in a saturating magnetic field. Young's modulus (E = _E², = density) shows anomalous temperature dependence at and below the magnetic transition temperature of each glass studied. These anomalies are interpreted as arising from the change of long-range spin coupling energy at the Curie temperature in a molecular field approximation. Comparison is made with similar effects in other crystalline and non-crystalline magnetic materials.     

Mössbauer studies on some glasses and crystals in the Na2O---Fe2O3---SiO2 system

Mössbauer absorption measurements have been made at room temperature on ⁵⁷Fe in iron sodium silicate glasses containing 3–15 mol% Fe₂O₃ and various iron alkali silicate crystals in order to study the state of iron in these glasses. The spectra of all the glasses gave one doublet with a quadrupole splitting varying from 0.73–0.78 mm s⁻¹, while those of Na₂O · Fe₂O₃ · 4 SiO₂ and 5 Na₂O · Fe₂O₃ · 8 SiO₂ crystals showed much smaller quadrupole splitting, 0.28 mm s⁻¹ and 0.10 mm s⁻¹, respectively, and an asymmetrical doublet of much narrower linewidth. When sodium was replaced by other alkali metals of larger size, such as K and Cs, in MFeSi₂O₆ and MFeSi₃O₈ crystals, the quadrupole splitting became wider and approached to 0.73 mm s⁻¹. Such a variation was not observed for glasses. These results suggest that a larger number of non-identical sites exist in iron sodium silicate glasses than in the corresponding crystals.     

The surface structure and catalytic properties of partially crystallized Fe---Si---B alloys

The surface structure of partially crystallized Fe₇₈Si₁₂B₁₀ alloys was investigated by means of X-ray diffraction, high resolution electron microscopy and Auger electron spectroscopy and was correlated with their catalytic properties. Highly dispersed minute -Fe particles were observed in the amorphous matrix. After chemical treatment of the partially crystallized Fe---Si---B alloys with NaOH solution, large stripes of B₂O₃ were discovered because of the aggregation of a boron-containing phase. Boron- or silicon-containing surface films were formed on the -Fe particles by diffusion, causing the deactivation of these alloy catalysts.     

Crystallization-nitriding process of FeSiB and FeSiBCuNb ribbons: influence of additive (Cu,Nb) pair and nitrogen on structure, magnetic and magnetostrictive parameters

Both conventional thermal treatments (CTTs) and nitriding thermochemical treatments (NTTs) are used to crystallize Fe₇₄Si₁₄B₁₂ and Fe_73.5Si_13.5B₉Cu₁Nb₃ melt spun ribbons. For the FeSiB sample, nitrogen is detected throughout the whole thickness, while nitrogen is observed only in the periphery of the (Cu–Nb) containing sample. Nitrogen diffusion is related to the crystallization. The remaining phase in the nanocrystallized FeSiBCuNb sample slows down the nitrogen diffusion. This kind of treatment applicated to FeSiBCuNb sample enables the formation of nanocrystallites with a grain size that is slightly smaller than that obtained following a CTT.     

Athermal photo-amorphization of As50Se50 films

A novel process for producing amorphous state, namely photo-induced transformation, is reported in a chalcogenide material, As₅₀Se₅₀, which in the crystalline phase is a molecular solid consisting of As₄Se₄ molecules. The crystalline-amorphous transition is athermal. Although the mechanism of photo-induced transformation to the amorphous state is not known, two possibilities are suggested: either photon-induced intramolecular bond-breaking leading to a cross-linked CRN-like network, or intermolecular bond-breaking resulting in an orientationally disordered molecular glass.     

Sub-Tg mechanical relaxation of a La55Al25Ni20 amorphous alloy

Dynamic mechanical properties of an amorphous La₅₅Al₂₅Ni₂₀ alloy were measured by a forced oscillation method in the temperature range from room temperature to 453 K, just below the glass transition temperature (T_g = 481 K). The internal friction at a constant frequency 62.8 rad/s of this alloy showed a peak at about 400 K and the peak position shifts with frequency. Structural relaxation reduces the magnitude of the relaxation peak but has little affect on the peak position. Using the time-temperature superposition process, master curves for storage E′ (ln ω) and loss E″ (ln ω) moduli are constructed. Activation energy of the relaxation obtained from shift factors is low, 100 kJ/mol, which is close to that for diffusion of the Al in Al and Ni in Al. The relaxation spectra are very broad with a half width of 2 3 decades.     

The effect of Pt-group metal additions on the thermal stability of Fe- and Ni-based glassy alloys

The influence of dilute concentrations (<10 at.%) of Pt-group metals (Re, Ru, Os, Ir, Pd and Pt) on the thermal-stability of melt-spun (Fe or Ni) Si₁₀B₁₂-based amorphous alloys has been investigated by differential scanning calorimetry. The stability of the Fe-based alloys, with the exception of those containing Pd or Pt, can be related to both the electronic and atomic-size differences between solvent and solute metal species, as we observed previously for other solutes from groups IVa–VIa. Addition of Ru, Pd or Pt to glassy NiSi₁₀B₁₂ has little effect on the stability, and no correlation with atomic size or electron concentration could be established.     

Synthesis and characterization of a novel non-linear optical material La2SrB10O19

A novel compound with the chemical formula of La₂SrB₁₀O₁₉ has been successfully synthesized from the La₂O₃--- SrO---B₂O₃ system via a solid state reaction. The powder X-ray diffraction data is reported. It is found that the data show little difference from that of La₂CaB₁₀O₁₉ which demonstrate that they are isostructural. The powder second harmonic generation effect of La₂SrB₁₎O₁₉ is about twice that of KH₂PO₄(KDP). The investigation of crystal growth is in progress.     

The enthalpy relaxation of amorphous Fe---Co alloys with metal-metalloid and metal-metal compositions

The enthalpy relaxation behaviour of metal-metalloid type (Fe_0.5Co_50.5)₈₃P₁₇ and metal-metal type (Fe_0.5Co_0.5) _90-Zr10 amorphous alloys was investigated with a DSC measurement. The annealing temperature (T_a) dependence of the annealing-induced reversible enthalpy relaxation evaluated with an endothermic showed the maximum at thesame T_a for the two alloys, but the magnitude of the relaxation was considerably smaller for the (Fe_0.5Co_0.5)₉₀Zr₁₀ alloy. Moreover, it was found that the amorphous (Fe_0.5Co_0.5)₉₀Zr₁₀ alloy has a larger atomic packing density and a higher activation energy of the enthalpy relaxation than the amorphous (Fe_0.5Co_0.5)₈₃P₁₇ alloy. Rhe small enthalpy relaxation and high activation energy for the amorphous (Fe_0.5Co_0.5)₉₀Zr₁₀ alloy were ascribed to the highly packed structure of the metal-metal type amorphous alloy.     

A comparison of the medium-range order in glassy GeS2 and Sb2S3

In amorphous (a-) GeS₂ there is only one medium-range order (MRO) dependent X-ray scattering feature, i.e., the ‘first sharp diffraction peak’ (FSDP), whereas in a-Sb₂S₃ all scattering features in the interval 1–2.4 Å⁻¹ are in fact MRO-dependent. The basic element of MRO in a-GeS₂ is a part of a chain of corner bound tetrahedra extracted from the high temperature form of c-GeS₂; in a-Sb₂S₃ it is a part of a crystalline-like (Sb₂S₃)_n band. Ordering of parts of these bands is characterized by a greater interband separation than in the crystal. By contrast with a-GeS₂, the MRO-dependent medium-angle scattering features in a-Sb₂S₃ are less sensitive to fluctuations of the interband (intercluster) ordering distance.     

Structural evolution in mechanical alloying of Co and B powders

X-ray diffraction and scanning electron microscopy were used to monitor the mechanical alloying of four different mixtures of cobalt and boron with atomic compositions Co₅₀B₅₀, Co₆₇B₃₃, Co₇₅B₂₅ and Co₈₀B₂₀, respectively. The process induces amorphization reactions depending on the boron content; an almost complete amorphization was reached for the Co₆₇B₃₃ and Co₈₀B₂₀ samples, where only minor traces of unreacted cobalt are present. Extended X-ray absorption fine structure data collected on the most amorphous sample confirmed the diffraction results. In all the samples, the formation of t-Co₂B was detected.