Elena Nikonenko

Modifying the structural phase state of fine-grained titanium under conditions of ion irradiation

The results from quantitative investigations into the structural phase state of finely dispersed titanium before and after implantation with aluminum ions are presented. Two types of α-Ti grains differing by phase composition, defect structure, and size are distinguished in the structure: fine grains in the range of 0.1–0.5 μm and coarse grains in the range of 0.5–5 μm. The presence of two types of TiO2 particles in the material, i.e., rounded particles found at dislocations in the bulk of the α-Ti grains and lamellar particles found only inside coarse α-Ti grains, is established. The formation of the Ti3Al phase is observed in the form of lamellar inclusions along the grain boundaries and rounded particles in triple joints. It is found that the particles of the TiAl3 phase are isolated with a smaller volume fraction than the Ti3Al phase; they are localized along the boundaries of coarse grains of the titanium matrix. It is established that the granular state and defect structure of the material change substantially after ion irradiation; i.e., the dislocation density and the fields of internal stresses in fine grains grow considerably, relative to the initial state of titanium.

Effect of thermal treatment and re-doping on the volume fraction of the γ′ phase in complex-doped Ni-Al-Cr-based superalloy

Phase transformations of complex-redoped Ni-Al-Cr-based superalloys under different thermal treatment are investigated by means of diffraction electron microscopy. Alloys are obtained via directional crystallization. The factors affecting the formation of the long-range atomic order of the γ′ phase (an ordered multicomponent phase based on superstructure L12) are established from the experimental results. It is shown that the degree of long-range order is directly dependent on the strengthening of the superalloy.

Intense formation of intermetallic phases during implantation of aluminum ions in titanium

The results from microstructure and phase composition investigations of titanium in different structural states (with average grain sizes of 0.3 μm, 1.5 μm, and 17 μm) are presented following Al ion implantation using the Mevva-V.RU source (irradiating dose, 1018 ion/cm2). The implanted multiphase layers are found to form on the base of α-Ti grains. The size, shape, and localization of the formed phases (TiO2, Ti2O, TiC, Ti3Al, Al3Ti) depend strongly on the grain size of titanium target. It is shown that the nanostructural particles of TiO2 phase are located mainly on dislocations in the body of target grains. A Ti2O surface layer is found to arise in titanium with a grain size of 17 μm. It is established that an ordered Ti3Al phase is located at a depth of more than 200 nm in the implanted layer along the bounaries of the titanium grains.

Study of creep and features of the dislocation structure in single crystals of Ni3Ge alloy

Data from investigating the dislocation structure of Ni3Ge alloy single crystals formed during creep are presented. The creep of the Ni3Ge single crystals with the [001] orientation of the deformation axis was studied. It was found that a fragmented substructure with varying degrees of disorientation occurs in the areas of macrolocalized deformation. A polycrystalline substructure consisting of fragments with a low dislocation density is formed in the local areas.

Structural and phase transformations in 0.3C-1Cr-1Mn-1Si-Fe steel after electrolytic plasma treatment

The paper presents the transmission electron microscopy (TEM) investigations on thin foils concerning phase transitions occurred in the type 0.3C-1Cr-1Mn-1Si-Fe alloyed steel after the electrolyte plasma treatment, i.e. carbonitriding at 850°C during 5 min. TEM investigations involve two points, namely: on the specimen surface and at 50 µm distance from the surface, i.e. in transition layer. It is shown that carbonitriding results in the formation of structures the properties of which are changed at a distance from it’s the specimen surface. Thus, the modified morphology of the steel matrix is represented mostly by high-temperature lamellar martensite on α-phase surface, while the intermediate layer is represented by massive martensite. After carbonitriding, the particles of the alloyed cementite and M2C0.61N0.39, M4(C,N), M7(C,N)3, M23(C,N)6 carbonitrides are observed in all layers inside α-phase crystals and at their boundaries. The concentration of carbon and nitrogen on the surface is considerably hig...

Change in the phase composition and defect structure of a multicomponent ordered Ni-based alloy upon high-temperature annealing

Phase transformations upon the high-temperature annealing of a multicomponent Ni-based alloy produced via direct crystallization are studied by diffraction electron microscopy. The alloy is annealed at T = 1000°C for a prolonged period. The phase composition is determined. The dislocation structure and behavior of the γ-phase during prolonged annealing are studied.

Scale Effects in the Structure of Modern Superalloys. Role of Nanoparticles

The structural state of the γ′ and γ phases of modern superalloys is considered in detail. A classification of the scale effects in the γ′ phase morphology is proposed.

Energy of planar defects in the Ni3Al phase: Theory and experiment

The Ni3Al phase with an L12 surperstructure exhibits a clearly pronounced positive temperature dependence of the yield stress. The nature of this phenomenon is still not clearly understood. The temperature dependence of the yield stress under consideration is determined, in many respects, by the structure of glide superdislocations and planar defects of these superdislocations involved in the L12 superstructure. A critical analysis is made of the current state of the art in the solution of the problem regarding the energy of antiphase boundaries in planes of an octahedron and a cube, as well as the energy of stacking faults in the Ni3Al phase.

The structure and phase composition of welded joint after deformation

The paper addresses the issue of the structure and phase composition of welded joint and focuses on their investigation after plastic deformation. The contribution of internal stresses to the formation of phase composition and fine structure of welded joint is shown herein. Electrode welding is used to obtain welded joint in St3 steel. Specimens are subjected to a quasi-static tensile deformation ranging from 0 to 5% under 370 MPa loading. TEM investigations on thin foil specimens allow studying the structure and phase composition within the heat-affected zone at 1 mm distance from base material and 0.5 mm from welding material. The degree of plastic deformation is shown for both base and welding materials and includes their morphology, phase composition, defect structure and its parameters. Long-range stresses are divided into plastic and elastic. Plastic deformation has no qualitative effect on the material structure, however, it modifies its quantitative parameters. With the increase of deformation deg...

Phase transformations in 0.34С–1Cr–1Ni–1Mo–Fe steel under the action of electrolytic plasma nitrocarburizing

Changes in the phase composition of 0.34С–1Cr–1Ni–1Mo–Fe steel during electrolytic plasma nitrocarburizing are studied via TEM. It is found that nitrocarburizing leads to considerable changes in the steel’s structure (phase composition, number of existing phases, and morphology).