N. V. Umnova

Strength and plastic properties of amorphous cobalt alloy wires produced by various melt quenching methods

The strength and plastic properties of amorphous wires produced by melt spinning, in-rotatingwater spinning (INROWASP), and the Taylor-Ulitovskii method are studied. The wire produced by the Taylor-Ulitovskii method is found to have the highest level of strength and plasticity. The fracture and lateral surfaces of the amorphous wires are subjected to fractographic analysis. The high plasticity of this wire is shown to be caused by sequential formation of various families of shear bands and their interaction. The structure of the surface layer in an amorphous wire is assumed to be controlled by thermomechanical treatment to form a one-dimensional nanoamorphous composite material.

Nature of the deformation crystallization of iron-based amorphous alloys upon megaplastic deformation

Specific features of the crystallization of amorphous alloys Fe83Cr13B4, Fe80B13Si7, Fe76Cr16Zr4.5B3C0.5, Fe58Ni25B17, Fe57Co24Cr16B3, and Fe50Ni33B17 during megaplastic deformation (MPD) in a Bridgman chamber have been studied at room temperature. It is found that the volume fraction of the crystalline phase formed in each of the amorphous alloys during deformation increases when its crystallization temperature decreases. The obtained results are explained on the assumption of adiabatic heating in a shear band and also the hypothesis regarding an increase in the concentration of excess free volume regions in shear bands during deformation.

Mechanical properties of “Thick” amorphous metallic wires produced by the Ulitovskii-Taylor method

The strength and plastic characteristics of thick (d = 40–120 μm) amorphous wires made of a model Co-based alloy and fabricated by the Ulitovskii-Taylor method are studied. They are found to have stable strength and plastic characteristics along the length. The plasticity of the thick wires is high, and they can form a full knot and undergo a load of 0.5 ultimate tensile strength in this state. The surface state and fracture surfaces of the amorphous wires are analyzed by scanning electron and optical microscopy. The wires are found to have a smooth lustrous lateral surface almost free of defects and to retain stable geometrical parameters along their length. Zones with different positions and frequencies of shear bands can form on the wire surface depending on the type of deformation action. The fracture surfaces of the thick amorphous wires are specific: a venous zone consists of several large pronounced principal “veins” and a rare network of adjoining secondary veins.

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.

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.

Conditions of formation of “thick” plastic amorphous Fe-Co microwires in Fe 75 Si 10 B 15 -Co 75 Si 10 B 15 system

Equilibrium and rapidly quenched Fe-Co-Si-B alloys are studied in Fe75Si10B15-Co75Si10B15 cross section. The polythermal cross section is developed in the range of melting and crystallization temperatures. Amorphous ribbons of alloys are produced by melt spinning, and rapidly quenched microwires in a glass sleeve with diameter of the metal core dcore = 10–100 μm are obtained by the Ulitovskii-Taylor technique. The structure and physical and mechanical properties of the alloys are studied. The concentration range of stability of “thick” amorphous plastic microwires with core diameter dcore ≥ 50 μm is determined using analysis of the phase diagram and content-property diagram. A special two-stage crystallization mechanism responsible for high glass-forming ability of microwires is established.

Conditions of formation of “thick” plastic amorphous Fe-Co microwires in Fe75

Equilibrium and rapidly quenched Fe-Co-Si-B alloys are studied in Fe75Si10B15-Co75Si10B15 cross section. The polythermal cross section is developed in the range of melting and crystallization temperatures. Amorphous ribbons of alloys are produced by melt spinning, and rapidly quenched microwires in a glass sleeve with diameter of the metal core dcore = 10–100 μm are obtained by the Ulitovskii-Taylor technique. The structure and physical and mechanical properties of the alloys are studied. The concentration range of stability of “thick” amorphous plastic microwires with core diameter dcore ≥ 50 μm is determined using analysis of the phase diagram and content-property diagram. A special two-stage crystallization mechanism responsible for high glass-forming ability of microwires is established.

Conditions of formation of “thick” plastic amorphous Fe-Co microwires in Fe75Si10B15-Co75Si10B15 system

Equilibrium and rapidly quenched Fe-Co-Si-B alloys are studied in Fe75Si10B15-Co75Si10B15 cross section. The polythermal cross section is developed in the range of melting and crystallization temperatures. Amorphous ribbons of alloys are produced by melt spinning, and rapidly quenched microwires in a glass sleeve with diameter of the metal core dcore = 10–100 μm are obtained by the Ulitovskii-Taylor technique. The structure and physical and mechanical properties of the alloys are studied. The concentration range of stability of “thick” amorphous plastic microwires with core diameter dcore ≥ 50 μm is determined using analysis of the phase diagram and content-property diagram. A special two-stage crystallization mechanism responsible for high glass-forming ability of microwires is established.

A mechanism of removal of a glass envelope from a “thick” amorphous Co-alloy wire prepared by the Ulitovsky-Taylor method

Optical and scanning electron microscopy are used to study a mechanism of removal of a glass envelope from a “thick” (D = 96 μm) amorphous wire prepared from a model Co alloy by the Ulitovsky-Taylor method. It is shown that the mechanism of destruction and removal of the glass envelope during pulling of the wire through a cylindrical tool with a hard rough coating is determined by the type and level of stresses that act in the amorphous metal core. The stresses that occur in the longitudinal direction owing to the difference in the linear expansion coefficients of the metal and the glass provide an easy chipping of long (5–15 wire diameters) fragments of the glass envelope. The local stresses induced by the bending of the wire even in the elastic region contribute to the effective destruction of the remaining small fragments of the glass envelope along the directions of the preferred formation of shear bands. High bending stresses arising from the plastic deformation of the amorphous metal core increase the efficiency of removal of the glass envelope, but lead to a decrease in the mechanical and magnetic properties of the metal core owing to the nucleation and propagation of a network of shear bands.