The preparation of ductile high strength Fe-base filaments using the methods of glass-coated melt spinning

High toughness glass-coated metallic fibres show great promise for use in composite materials as reinforcement for brittle matrixes such as fine ceramics. This paper describes the glass-coated melt spinning of austenitic steel and Fe-B base alloys in order to prepare a ductile high strength filament. The toughness was estimated from the area of the stress-strain curves of the filament obtained. Continuous high toughness steel filament, which had a maximum toughness of 6600 MPa% with a tensile strength of 3050 MPa and an elongation of 3.1% was obtained from the molten state at 1600 K for a winding speed of 7.95 m sec^–1. The filament was 3×10^–6m diameter and polycrystalline with a grain size of 1000×10^–10m. The crystal structure of the filament was a single b c c phase and the phase transformed into a stable f c c structure by heat treatment at 1073 K for 600sec. Ductile filaments of Fe_78-x Co₅Ni₅Cu₂B₁₀M _x (M _x Cr_5–20, Cr₅Si₃, Cr₅Co₅, Cr₅Ni₅, Cr₁₀Mo_0.5, Cr₁₀Nb_0.5) alloys were also successfully produced. The Fe_67.5Co₅Cr₁₀Ni₅Cu₂B₁₀Mo_0.5 filament had the highest toughness of 13 900 MPa% with tensile strength of 3760 MPa and an elongation of 4.8%. The filament had a single b c c phase.     

Enhancement of superconductivity in Pb-Bi-Sn and Pb-Bi-In alloy filaments produced by glass-coated melt spinning

The enhancement ofT _c in Pb-Bi-Sn and Pb-Bi-In system alloy filaments produced by glass-coated melt spinning was investigated as a means of producing a new type of superconducting filament with highT _c. Long filaments of Pb-Bi-Sn alloy withT _c higher than 10 K and Pb-Bi-In alloy withT _c higher than 9 K were obtained from the molten state at a temperature of 1500 K with a winding speed of 2.63 m sec^–1. For example, a Pb₄₅Bi₃₅Sn₂₀ filament withT _c of 10.1 K was 15 m in diameter and polycrystalline with a grain size of 100 nm. The structure of the filament was a mixture of , tin and bismuth phases and a metastable phase of mixed structure of bismuth and supersaturated solid solution of tin in -phase was detected. TheT _c of the filament decreased on heat treatment. A metastable phase of mixed structure of bismuth and -phase was also detected for a Pb₄₅Bi₄₅In₁₀ filament withT _c of 9.3 K. As the metastable phase for the Pb-Bi-In filament was more unstable than that for the Pb-Bi-Sn filament, theT _c of the filament was drastically decreased by heat treatment. The metastable phase was considered to play an important role in the enhancement ofT _c for Pb-Bi-Sn and Pb-Bi-In alloy filaments.     

Mechanical properties and microstructure of high toughness Fe-base filaments produced by glass-coated melt spinning

High toughness Fe_57.5Co₅Cr₁₅Mn₁₀Cu₂B₁₀Ti_0.5 filaments having a high tensile strength of 1740 M Pa and high elongation of 11.0% were produced by the method of glass-coated melt spinning. A noticeable feature of the stress-strain curves of the filament was that rapid hardening to a high stress-level of more than 1500 M Pa was reached in the first few per cent of tensile elongation. The filament was 14.5m diameter and micropolycrystalline with a grain size of 27 nm. The crystal structure of the filament was a mixture of bcc and fcc phases and the two phases were distributed homogeneously in the filament. The high toughness of the filament related to its micropolycrystalline structure and the uniformly mixed structure of bcc and fcc phases. After heat treatment at 573 K for 600 sec, the filament developed a higher toughness with a tensile strength of 2150 M Pa and an elongation of 12.0%.     

A method for preparation of a high-quality high temperature superconducting ceramics

An improved method for hot pressing of high temperature superconducting (HTSC) powders prepared by conventional solid phase synthesis of the initial BaCO₃, CuO and Ln₂O₃ allows one to obtain HTSC targets and magnetic shields possessing a high degree of homogeneity. By sputtering such targets HTSC films with critical current density of 3.3·10⁶ A/cm² have been deposited. Shields, prepared according to this method, show a shielding coefficient of 10⁵ andH _c of 79 Öe in the constant magnetic field and in the alternating magnetic field the amplitude is 90 Öe in the frequency range of 70–3000 Hz.     

The preparation,properties and applications of some glass-coated metal filaments prepared by the Taylor-wire process

The Taylor-wire method offers a versatile and intrinsically inexpensive route for the manufacture of glass-coated metal filaments a few micrometres in diameter in a single operation directly from the melt. The preparation by this process of a number of microcrystalline and amorphous microwires is reported. Materials investigated have included copper, four different Ni-Si-B alloys and a Co-Mo alloy. The resultant properties of the microwire products prepared from these materials are summarized. One potential application for microwire is in the area of composite materials and data are presented outlining the preparation directly from microwire of metal filament-reinforced glass-matrix composites. In conclusion, a number of alternative potential applications for microwire are briefly discussed.     

Specific-heat anomaly near superconducting transition in high temperature superconductors

A brief appraisal of the current state of understanding on the specific heat anomaly nearT _c in the oxide superconductors is presented. Spectacular specific heat double transitions are explained with plausible models.     

An experimental study on the melt spinning of AA2618 alloy

The commercial AA2618 alloy was treated through melt spinning at rotation speeds of 20 and 40 ms^–1, respectively. The melt-spun ribbons were characterised by a combination of optical microscopy (OPM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Microstructural evolution of ribbons in the continuous heating process was investigated. Microhardnesses of samples treated under different conditions were measured. It was found that due to the low solubilities of iron and nickel Al _x FeNi was very prone to precipitate in AA2618 alloy. At chilling sides of melt-spun ribbons fine Al _x FeNi particles presented along the grain boundaries, while at free sides Al _x FeNi presented not only along the grain boundaries but also in the interior of grains. The microhardnesses of melt-spun ribbons decreased significantly from chilling surfaces to free surfaces. During heating Al _x FeNi precipitated uniformly throughout the matrix until melting, which was one of the reasons responsible for the lowering of hardness.     

The influence of short-range magnetic correlations on the superconducting transition temperature

Taking into account correlations between well-defined localized magnetic moments in a dilute magnetic system, we derive an expression for the super-conducting transition temperature which is different from Bennemann's theory. In particular it is shown that the influence of short-range magnetic correlations in the vicinity of a magnetic phase transition on the superconducting transition temperature is twofold: (1) There are large corrections to the Abrikosov-Gor'kov theory. (2) For a certain choice of parameters the phase diagram in the temperature versus concentration plane shows a break (where the system is normally conducting) between two superconducting regions.     

The superconducting transition temperature of multilayer superconductors: The frustratedXY-Josephson model

The superconducting transition temperature of multilayered superconducting structures of the S-N(D)-S type in the RVB theory is defined taking into account the resonance pair “tunneling” between superconducting layers. The Josephson array defectivity is considered with the frustration parameters.     

The superconducting transition temperature of multilayered superconductors. The frustratedXY-Josephson model

The superconducting transition temperature of multilayered superconducting structures of the RVB theory for the S-N(D)-S type is defined taking into account the resonance pair “tunneling” between superconducting layers. The Josephson array defectivity is considered with the frustration parameters.     

The use of NbTiTa as a high field superconducting alloy

NbTi-based alloys containing 8% and 25% tantalum have been studied for use at fields around 12 tesla and at temperatures between 2 K and 3 K. These materials have significantly higher current densities at reduced temperatures than other NbTi-based alloys. Using the results of these studies, a 10,000 A, nominal 12 tesla conductor has been designed and is presently being fabricated for use in a test coil for the Lawrence Livermore Laboratory HFTF. The alloy selected for that conductor is Nb-43% Ti-25% Ta.     

Morphology and phase transition of high melt temperature crystallized poly(vinylidene fluoride)

When PVDF is crystallized at temperatures above 155°C it presents a multiform morphology composed of ringed, non ringed and mixed spherulites. Infrared spectroscopy showed that the ringed spherulites are formed exclusively by the phase when crystallization takes place at temperatures below 155°C. Higher temperatures induce a solid-state phase transformation in these structures, increasing the amount of phase with crystallization time. The rate at which this transformation takes place increases with crystallization temperature. The non ringed spherulites, only formed at crystallization temperatures above 155°C, consist predominantly of the phase, crystallized from the melt, with small phase inclusions. The melt process of the different spherulites, observed by optical microscopy and calorimetric measurements (DSC) showed that the melt temperature of the phase, originated from the phase transition, is 8°C higher than that crystallized directly from the melt. Optical micrographs of samples heated up to 186°C and quickly cooled allowed visualization of the ringed spherulite regions which underwent the phase transformation at different crystallization times and temperatures.     

Quantum oscillations of the superconducting transition temperature in Al-SiO systems

We report measurements on the superconducting transition temperature T _cand the normal resistance R _nof quench-condensed pure and granular aluminum films. The changes of the superconducting transition temperature are characteristically dependent on the coating film thickness and are inversely dependent on the Al film thickness. The observed oscillations of the transition temperature are interpreted in the framework of the theory of quantum oscillations developed by Kagan and Dubovskii.This work was supported in part by the Deutsche Forschungsgemeinschaft.     

Fluctuation conductivity of tin films below the superconducting transition temperature

Measurements have been carried out of the temperature dependence of the fluctuation-induced excess electrical conductivity of thin (thickness much less than the Ginzburg-Landau coherence length) superconducting films of tin below the transition temperature. Two types of specimen were investigated: (a) films deposited on a glass substrate held at 300 K and (b) films deposited on a glass substrate at 300 K and then covered by a protective layer of germanium. Special care was taken to ensure sample homogeneity. Analysis of the results shows that the fluctuation parameter, ε_c, is not affected by the germanium layer. Its value is, however, much larger than that predicted by the theory of Kajimura, Micoshiba, and Yamaji.     

The superconducting transition temperature for La1−x Gd x

The deviation of the superconducting transition temperature from the Abrikosov-Gorkov behavior in the case of La_1−xGd _x is explained considering the presence of short range spin-glass at low temperature. The theoretical results show good agreement with the experimental data.     

The interaction of phase-slip centers in superconducting filaments

Theoretical step structures for ideal homogeneous filaments based on the interactions implicit in the simple phase-slip-center model of Skocpol, Beasley, and Tinkham are displayed explicitly.Research supported in part by NSF and ONR.Senior U.S. Scientist awardee of Alexander von Humboldt Foundation.     

Relevance of free-surface temperature to thermal and kinetic factors in melt spinning

The relationship between the free-surface temperature history and the thermal and kinetic factors involved in melt spinning has been examined using a thermokinetic model for rapid solidification. Results show that the relationship is quite substantial. Measurement of the free surface temperature history can lead to the estimation of some of the factors involved which are otherwise very difficult to measure. Once these factors are determined, the real situation in rapid solidification can be modelled.Nomenclature A Pre-exponential coefficient for the nucleation rate expression - C _p Specifie heat with C ₁ and C _s representing that for liquid and solid, respectively - D The pre-basial constant for the crystal growth kinetic model - The thickness of the solidifying slab - G ^* Activation barrier for homogeneous nucleation - G Gibbs free energy change for an atom jumping from liquid to solid - Atomic jump frequency - h Heat transfer coefficient - I Nucleation rate with I _s and I _t representing the steady state and transient nucleation rate, respectively - k Boltzmann's constant - K Heat conduction coefficient with K ₁ and K _s representing that for liquid and solid, respectively - L Latent heat - n The power index of the crystal growth kinetic model - N ^* Number of atoms in the critical nucleus - Density of the material with ₁ and _s representing that for liquid and solid, respectively - t Time coordinate - T ₁ Initial temperature of the cooling substrate - T ₂ Initial liquid temperature - T _I Interface temperature - T _m Melting point - T _n Nucleation temperature - T Undercooling: T=T _m-T _I - t _s The time at the onset of solidification - V Interface velocity - x Space coordinate