Using scanning and transmission electron microscopy, we studied silicon particles formed during the solidification of Al-7%Si alloy when different modifying mixtures were introduced into the melt: (1) a mixture of ultrafine powders Na₃AlF₆ + K₂ZrF₆ + TiO₂ + ZrO₂; (2) K₂ZrF₆; and (3) the flux Arsal. By differential scanning calorimetry, it was established that modifying mixtures significantly influenced the temperature of the solidification processes. The formation of two types of Si crystals was established. The first type of Si crystals precipitated during the solidification of the eutectic mixture (α-Al + Si) in the form of needles or plates. The second type of Si crystals was segregated from eutectic Al-phases or segregated from the solid phase α-Al upon cooling in the solid state. The introduction of modifiers led to a shift in solidification temperatures. When fluoride salts were used, there was an increase in the temperature of eutectic solidification. Silicon crystals were large (up to 10 µm), with a local excess of aluminum concentration.

By transmission diffraction electron microscopy, study of the changes in the phase composition arising in 0.3C-1Mn-1Si-Fe steel upon plasma electrolytic nitrocarburizing with increasing distance from the modified surface is performed. It is found that, with increasing distance from the surface, the list of carbonitride phases and their volume fraction are reduced. The morphology of the steel matrix is changed.

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 higher. The modification of quantity is observed in the distribution and the volume fraction of carbide phases with the distance from the specimen surface, while the amount of carbonitride phases significantly reduces. Also, it is shown that carbonitriding leads to a complete relaxation of the internal local stresses on the specimen surface, while in the intermediate layer plastic stresses are observed.

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).

This work deals with the study of changes in the dislocation structure and quantitative characteristics, as well as morphological components, of 0.34Cr-1Ni-Mo-Fe steel before and after plasma electrolytic hardening. According to the electron microscopic studies of the fine structure of 0.34Cr-1Ni-Mo-Fe steel before and after plasma electrolytic hardening, 0.34Cr-1Ni-Mo-Fe steel is a multiphase material containing an α-phase, a γ-phase (retained austenite), and a cementite and carbide phase. It was revealed that, morphologically, the α-phase in the initial state, generally, is present in the form of: lamellar pearlite with a volume fraction of 35%, a ferritocarbide mixture with a volume fraction of 45%, and fragmented ferrite with a volume fraction of 20% of the material. After surface hardening, the morphological components of the structure changed: packet–lamellar martensite with volume fractions of 60% and 40%, 5% and 7% of γ-phase as residual austenite in the crystals of packet–lamellar martensite, 0.6% and 1.5% of cementite in crystals of packet–lamellar martensite, and 0.15% and 0.35% of complex carbide M₂₃C₆ in crystals of packet–lamellar martensite, respectively, were observed. The quantitative characteristics of the dislocation structure were estimated by the following calculated indices of packet and lamellar martensite: scalar (ρ) and excess (ρ±) density of dislocations, the value of the curvature-torsion of the crystal lattice (χ), the amplitude of long-range internal stresses (σd), and the amplitude of shear stresses (σ_L), according to which the plastic nature of the bending-torsion of the crystal lattice was confirmed (σ_L > σd).