G. F. Korznikova

The mechanism of nanocrystalline structure formation in Ni3Al during severe plastic deformation

The microstructure evolution of the intermetallic compound Ni3Al during severe deformation by torsion under high quasi-hydrostatic pressure, which eventually results in the formation of a disordered nanocrystalline structure with a high level of internal stresses, was investigated as a function of the amount of shear strain. At the microstructural level, the crystals were first fragmented by the propagation of twins, then nanosized equiaxed crystallites with high misorientations were formed. At the macroscopic level, there is evidence that the cold-worked structure first formed at the sample surface and then propagated into the whole volume.

Nanocrystalline structure and phase transformation of the intermetallic compound TiAl processed by severe plastic deformation

Abstract Bulk samples of nanocrystalline TiAl were produced by severe plastic deformation. Different amounts of cold work lead to different nanocrystalline structures and phase contents. Based on transmission electron microscopy and X-ray data an assumption has been made to explain the origin of the observed structural changes.

Saturation magnetization and Curie temperature of nanocrystalline nickel

Abstract Bulk samples of nanocrystalline Ni were produced by severe plastic deformation consolidation of ball-milled powders. The processed samples are characterized by reduced values of saturation magnetization and Curie temperature. Relying on transmission electron microscopy and X-ray data, an assumption has been made to explain the origin of the observed phenomena.

THE CHANGE IN THE EFFECTIVE MAGNETIC MOMENT IN GADOLINIUM AFTER SEVERE PLASTIC DEFORMATION

Abstract This paper presents the results of an experimental study of the temperature dependence of the magnetization and paramagnetic susceptibility in pure gadolinium after severe plastic deformation. A significant decrease in the effective magnetic moment was established, which is explained on the basis of an analysis of the structural changes in the sample after deformation.

The study of domain structure of submicron grained cobalt and its changes during heating

Abstract The results of an experimental study of the domain structure of cobalt with a submicron-grained structure (d≈0.1 μm) at room temperature and during heating are given. For comparison the domain structure of coarse-grained (d = 10 μm) specimens are studied as well. It is established that the decrease of grain size in the structure slightly changes the shape of the domain structure of a striped type. At heating in the temperature range of 470–570 K, an increase of domain width is observed and then near 570 K the change of the domain wall direction by π/2 in the specimen plane occurs. The explanation of observed effects proceeding from the analysis of temperature dependence of cobalt magnetocrystalline anisotropy constants is given.

Magnetic hysteric properties and saturation magnetization of nanocrystalline iron

The paper presents the results of experimental studies of bulk nanocrystalline pure iron produced by two-steps severe plastic deformation. The processed samples are characterized by enhanced values of coercivity and saturation in comparison with a coarse grained state. Annealing leads to partial restoration of the properties. High-temperature (1073 K) annealing results in complete restorations of properties due to recrystallization. Transmission electron microscopy and X-ray analysis were used for structural analysis.

Structure and property changes in intermetallic compounds during severe plastic deformation

Abstract The processing of intermetallic compounds by severe plastic deformation (SPD) methods is reviewed. In Ni3Al-based massive compounds or multiphase materials this leads to a disordered nanocrystalline structure. In TiAl, high-temperature SPD by multi-step forging produces sub-microcrystalline materials, but room-temperature SPD by high-pressure torsion results in a partial phase transformation. This is also the case for the σ phase of multiphase FeCrCo alloys.

Properties of Ni-based amorphous ribbons consolidated by high pressure torsion

Two amorphous ribbons, of compositions (Ni56Cu2)Zr18Ti16Al3Si5 and (Ni36Cu23)Zr18Ti14Al5Si4, were subdued to the similar process of cold consolidation by the high pressure torsion (HPT) method. The first ribbon, that revealed higher thermal stability of the amorphous phase, higher GFA and better mechanical properties like tensile strength, Young modulus and hardness, partially crystallized in the HPT process. The second ribbon, revealing lower Tg and Tx temperatures, tensile strength and hardness, could be consolidated preserving amorphous structure. Such result suggests that the thermal stability against crystallization was not responsible for the preservation of the amorphous phase in the cold consolidation by the HPT. It rather seemed that a proper relation of the undercooled liquid temperature range to the local temperature increase during consolidation is suggested and it was a decisive parameter.

Magnetic properties of terbium with submicrocrystalline structure

The influence of the structural state of terbium on its magnetic properties is studied. It is shown that in the submicrocrystalline state remagnetization occurs following a wide hysteretic loop and a helical antiferromagnetic order does not form. Unlike the coarse-grained state, the magnetization value in the submicrocrystalline state is 5 times less, and the temperature of magnetic transformation is lower by 14 K.

Study of the domain structure of submicron-grained nickel

Abstract The results of an experimental study of the domain structure of nickel with submicron-grained structure ( d = 0.1 μm ) by the Lorenz method are given. For comparison, the domain structure of coarse-grained ( d = 10 μm ) specimens are studied as well. It is established that the decrease in grain size from 10 to 0.1 μm in the structure causes no changes in the domain structure configuration. The observations are explained from the analysis of nickel magneto-crystalline and induced anisotropies.