V. V. Molokanov

Nanocrystallization of bulk ZrCuTi metallic glass

The phase transformations during heating of Zr 30 Cu 60 Ti 10 bulk metallic glass were studied by differential scanning calorimetry, dilatom-etry, X-ray diffraction, transmission and high resolution electron microscopy. The crystallization of bulk metallic glass was found to occur in several stages. According to X-ray diffraction studies the structure was closely similar to amorphous structure when the sample was heated to the end of the first DSC sub-peak (781 K). However, the volume effect of the first stage of transformation is 1.6%; it forms about 80% of total volume effect of the crystallization (2%). A change of the shape of the diffraction maxima has been analyzed for the cases of structure relaxation and nanocrystalline structure formation. The nanocrystalline structure with very fine grain size was found to form during first stage of crystallization. The grain size of the nanocrystals was 1-5 nm.

Specific features of magnetic properties of “thick” microwires produced by the Ulitovsky-Taylor method

The magnetic properties of initial and heat-treated Co69Fe4Cr4Si12B11 microwires in a glass shell with the diameter D = 125 μm and the diameter of the amorphous metallic core d = 90 μm produced by the Ulitovsky-Taylor method have been studied. It has been found that the magnetic characteristics, in particular, the saturation field HS and the coercive force HC of the samples annealed at a temperature T < 300°C do not differ from HS and HC of the initial microwire, and those of the samples annealed at T ≥ 400°C increase by almost one order of magnitude. The obtained experimental data have been explained by the structural features of the microwires. The near-surface values of HS and HC at T < 300°C are found to be larger than the bulk values by a factor of 5–10. These experimental data have been explained by the existence of structural and chemical ingomogeneities in the near-surface layer, which are inherent in amorphous materials. This difference decreases with a further increase in the annealing temperature, but HS and HC increase substantially. This fact has been explained by the beginning of the microwire crystallization.

Initial stages in the decay of the amorphous phase in the bulk metallic glass Zr-Cu-Ti

Using methods of x-ray diffraction analysis, differential scanning calorimetry, dilatometry, and transmission electron microscopy, we have investigated the initial stages of decay of the amorphous phase in a bulk metallic glass based on zirconium. We found that crystallization of the bulk metallic glass proceeds in several stages, where in the first stage the bulk conversion effect is equal to more than 1.6%, or about 80% of the total bulk crystallization effect. We showed that the first stage of decay of the amorphous phase in the bulk metallic glass Zr29Ti11Cu60 leads to the formation of a nanocrystalline structure with a grain size of 1–5 nm. We have analyzed the change in the shape of the diffraction maximum during the formation of the very fine nanocrystalline structure.

Formation and structure of nanocrystals in bulk Zr50Ti16Cu15Ni19 metallic glass

The possible formation of a nanocrystalline structure in controlled crystallization of a bulk Zr50Ti16Cu15Ni19 amorphous alloy has been studied using differential scanning calorimetry, transmission and high-resolution electron microscopy, and x-ray diffraction. It was established that crystallization of the alloy at temperatures above the glass formation point occurs in two stages and brings about the formation of a nanocrystalline structure consisting of three phases. Local spectral x-ray analysis identified the composition and structure of the phases formed.

“Thick” amorphous wires in the Fe75Si10B15–Co75Si10B15–Ni75Si10B15 system: Fabrication, structure, properties

Samples of rapidly -quenched ribbons and wires with a diameter of metal core of dс= 50–200 μm within the ternary eutectic system Fe75Si10B15–Co75Si10B15–Ni75Si10B15 were obtained by the melt spinning and Ulitovsky–Taylor methods. The liquidus surface and crystallization surface of the amorphous alloys were constructed on the basis of the results of investigations of the thermal, mechanical and magnetic properties of the system alloys; the concentration ranges of amorphous alloys with various crystallization mechanisms and the ranges of amorphous alloys with the positive and negative Villari effect were determined. The concentration range of compositions favorable for obtaining amorphous wires with high glass-forming ability was determined. The comparative study of the structure and properties of the “thick” wires samples was carried out for two models alloys: Co71Fe4Si10B15 and Fe31Co34Ni10Si10B15. It was found that the wires possess a new complex of high strength, ductile, elastic, and soft magnetic properties. The prospects for application of “thick” ferromagnetic amorphous wires associated with the development of new types of structural and functional materials were considered.

Effect of quenching conditions on the structure and properties of a “thick” microwire fabricated by the Ulitovskii-Taylor method

The effect of quenching conditions on the mechanical and magnetic properties of a meltquenched wire with a core diameter of 50 μm, which is made of a model soft magnetic Co69Fe4Cr4Si12B11 alloy and is fabricated by the Ulitovskii-Taylor method, is studied. The highest set of mechanical and soft magnetic properties of a wire is achieved when it is quenched from the upper position of a quenching stream. The lowering of the position of the quenching stream degrades the mechanical and magnetic properties of the wire at a retained amorphous structure in it.

Magnetic structure and properties of a bulk Fe72Al5P10Ga2C6B4Si1 alloy in the amorphous and nanocrystalline states

The structure forming under controlled crystallization of a bulk Fe72Al5P10Ga2C6B4Si1 amorphous alloy has been studied using differential scanning calorimetry, transmission electron microscopy, and x-ray diffraction. Crystallization of the alloy was established to result in the formation of a nanocrystalline structure consisting of three phases. The domain structure and magnetic properties of amorphous and nanocrystalline samples were investigated using the magnetooptic indicating film technique (MOIF) and a vibrating-sample magnetometer. The coercive force and the saturation magnetization of the amorphous samples were found to be 1 Oe and 130 emu/g, respectively. It was shown that the formation of the nanocrystalline structure entails a dramatic decrease in domain size (down to 1–4 µm) as compared to an amorphous sample (∼1 mm). Simultaneously, a decrease in the saturation magnetization and a strong increase in the coercive force of the samples were observed.

Effect of thermal treatment on the microstructure and magnetic properties of a bulk amorphous Fe72Al5P10Ga2C6B4Si1 alloy

The structure and chemical composition of the phases that form in the controlled crystallization of a bulk amorphous Fe72Al5P10Ga2C6B4Si1 alloy are studied by differential scanning calorimetry, transmission electron microscopy, and x-ray diffraction. It was established that, when the alloy is annealed at a temperature above the glass transition point, a nanocrystalline structure consisting of three phases arises. The magnetic properties of amorphous and nanocrystalline samples were studied with a vibrating-sample magnetometer. The coercive force and saturation magnetization of amorphous samples were found to be 1 Oe and 130 emu/g, respectively. The structure and chemical composition of the forming phases and their correlation with the magnetic properties of the samples were determined.

Application of thermal analysis technique for development of technology of melt preparation to obtain “thick” amorphous Co-alloy microwires

The thermal analysis technique of estimating the ability of a melt to overcool is used to determine the optimum technological regimes of melt preparation in all the production stages of amorphous wires. The temperature range of high-temperature melt homogenization and the regimes of precursor extraction and melting are defined for the model Co69Fe4Cr4Si12B11 alloy. With use of the established regimes of heat treatment, the precursor melting is conducted and the samples of high-ductile amorphous microwires with a diameter 200 μm are produced by the Ulitovsky–Taylor method.

Structure and properties of amorphous finemet alloy microwires produced by the Ulitovskii-Taylor method

Amorphous Fe73.5Si13.5B9Nb3Cu1 alloy microwires 19–50 μm in diameter are fabricated by the Ulitovskii-Taylor method. The mechanism of crystallization of the amorphous microwires is shown to be analogous to the mechanism of crystallization of an amorphous ribbon made of the same alloy. Microwires up to 30 μm in diameter are found to exhibit ductility upon bending. The near-surface magnetic properties of the microwires are shown to depend on the microwire diameter. The magnetic properties of the amorphous microwires are highly sensitive to elastic tensile and torsional strains in an ac magnetic field.