K. V. Alsaraeva

Evolution of Al–19·4Si alloy surface structure after electron beam treatment and high cycle fatigue

Abstract Processing of Al–19·4Si alloy by high intensive electron beam has been carried out, and multiple increase in fatigue life of the material has been revealed. Investigations of structure and surface modified layer destruction of Al–19·4Si alloy subjected to high cycle fatigue tests to fracture have been carried out by methods of scanning electron microscopy. The factors responsible for the increase in fatigue life of Al–19·4Si alloy have been revealed and analysed.

Surface layer structure degradation of rails in prolonged operation

By methods of optical, scanning and transmission electron microscopy and microhardness measurement the transformation regularities of structure-phase states, defect substructure, fracture surface and mechanical properties of rail surface layer up to 10 mm deep in process of long-term operation (passed tonnage of gross weight 1000 mln. tons) were revealed. According to the character of fracture and level of structure imperfection the three layers were detected: surface, transition and boundary ones. It has been shown that the surface layer ~20 μm in thickness has a multiphase, submicro- and nanocrystalline structure and it contains micropores and microcracks. The increased density of bend extinction contours at 2 mm depth from the tread contact surface was noted, and it was shown that the maximum amplitude of stress fields was formed on the interphase boundary the globular cementite particle–matrix. The evaluation of stress fields was done.

Fatigue life of silumin treated with a high-intensity pulsed electron beam

The regularities of the formation of the structure of silumin irradiated with a high-intensity electron beam in different modes are revealed using optical and scanning electron microscopy. The optimum irradiation mode that allows one to increase the fatigue life of this material by a factor of up to 3.5 is determined. The probable causes of the observed effect are investigated.

Fractography of the fatigue fracture surface of silumin irradiated by high-intensity pulsed electron beam

Irradiation mode has been revealed allowing to increase the silumin fatigue service life in three times, it was established that this fact is caused by the formation of multi-modal, multi-phase, submicro - and nano-structure able to lead to a significant increase in the critical length of crack.

Evolution of the defect subsystem of structural steel with bainite structure on deformation

Transmission electron diffraction microscopy permits analysis of the evolution of the defect subsystem in 30X2H2MΦA steel with bainite structure, with up to 36% compression. The influence of the deformation on the scalar dislocation density, the volume of the material with microtwins, the fragment dimensions, the number of stress concentrators, and the amplitude of lattice curvature and torsion is determined. In the plastic deformation of bainitic steel, the scalar dislocation density and the volume of the material with deformational microtwins increase, along with the number of stress concentrators and the amplitude of lattice flexure and torsion, while the mean longitudinal dimensions of the fragments decrease. The stages in parameter variation are identified for the steel substructure. Possible explanations of these stages are discussed. In the first stage of loading (0 < ε < 18%), the deformation is due to motion of the dislocations; in the second stage (18 < ε < 36%), it is due to the motion of dislocations and twins.

Structure-phase states of silumin surface layer after electron beam and high cycle fatigue

Modification of eutectic silumin surface has been implemented by high-intensity pulsed electron beam. The irradiation mode has been revealed; it allows increasing silumin fatigue life in more than 3.5 times. It has been established that the main reason of this fact is the formation of a multiphase submicro- and nanosized structure. It has been elicited that the most danger stress concentrators are large silicon plates situated on the surface and near-surface layers.

Structure, phase composition, and defect substructure of differentially quenched rail

Differential quenching of rail by compressed air is a promising hardening method. Transmission electron microscopy is used for layer-by-layer analysis of differentially quenched rail. Quantitative parameters of the structure, phase composition, and dislocational substructure are determined and compared for different quenching conditions. Differential quenching of rail by compressed air in different conditions is accompanied by diffusional γ → α transformation. Three morphologically distinct components are formed: grains of plate pearlite, structure-free ferrite, and ferrite-carbide mixture. Gradient behavior is noted in the resulting structure: the state of the surface layer in the rail steel depends not only on the quenching conditions but also on the direction of observation and the depth of the layer being analyzed. Dislocational substructure is obtained; not only dislocational chaos, but also reticular, cellular, and fragmented dislocational substructure.

Surface gradient structure-phase states formation under differentiated quenching of 100 meter rails

Using transmission electron microscopy methods the layer by layer analysis of rails differentially quenched in different regimes is carried out on different scale levels. It is shown that the differentiated quenching of rails is accompanied by the formation of morphologically different structure, being produced according to the diffusion mechanism of γ-α transformation and consisting of plate perlite grains, free ferrite grains and grains of ferrite-carbide mixture. The gradient character of the changing of structure, phase composition and dislocation substructure parameters in the surface layer of rails head is established. It is revealed that the interfaces between globular cementite particles-matrix are the most dangerous stress concentrators.

Laws of the deformation-induced structural transformation in bainitic steel

The evolution of the defect and carbide subsystems of steel with a bainitic structure during deformation by compression is quantitatively analyzed by transmission electron diffraction microscopy and X-ray diffraction. The strain dependences of the parameters of a dislocation substructure and a carbide phase are determined, and the possible causes of stages in their changes are discussed.

Fatigue life of silumin irradiated by high intensity pulsed electron beam

The electron-beam processing of silumin, leading to the evolution of structure-phase state of its surface is carried out. It has been shown that this alloy is a multiphase material and contains, except an aluminum-based phase, the particles of intermetallic compounds of Al-Si- Fe-Mn. It is shown that electron beam treatment of the eutectic silumin surface increases the fatigue service life more than in 3.5 times. The analysis of structure-phase states modification of silumin subjected to electron beam treatment with the following fatigue loading up to the failure is carried out by methods of optical and scanning electron diffraction microscopy. Analysis of the surface layer structure revealed the sources of nucleation of submicrocracks. It is revealed that the large silicon plates located on the surface and in the subsurface layer are the most dangerous stress concentrators.