A. P. Semin

Formation features of structure-phase states of Cr–Nb–C–V containing coatings on martensitic steel

By methods of modern physical materials science the investigations analysis of phase composition, defect substructure, mechanical and tribological properties of Cr–Nb–C–V containing coatings formed in surfacing on martensitic wear resistant steel Hardox 450 were carried out. It was shown that surfacing resulted in the formation of high strength surface layer 6 mm in thinness. This layer had wear resistance 138 times greater than that of the base and friction coefficient 2.5 times less. On the basis of the investigations by methods of X-ray structural analysis and transmission diffraction electron microscopy it was shown that increase strength and tribological properties of surfacing metal were caused by its phase composition and state of defect substructure, namely, availability of interstitial phases (more than 36%) and martensitic type of α-phase structure.

Electric arc surfacing on low carbon steel: Structure and properties

By the methods of modern materials science, the structure-phase state and microhardness distribution along the cross-section of single and double coatings surfaced on martensite low carbon steel by alloy powder-cored wire were studied. It was established that the increased mechanical properties of surfaced layer are determined by the sub-micro and nanodispersed martensite structure formation, containing iron borides forming the eutectic of lamellar form. The plates of Fe2B are formed mainly in the eutectic of a single-surfaced layer, while FeB is formed in a double-surfaced layer. The existence of bend extinction contours indicating the internal stress fields formation at the boundaries of Fe borides-α-Fe phases were revealed.

FORMATION AND EVOLUTION OF STRUCTURE-PHASE STATES IN RAILS AFTER DRAWN RESOURCE

By optic and transmission electron microscopy, the regularities of the transformation of structural-phase states, the defective substructure of the rail surface layer to the depth of 10 mm under long-term operation (passed gross tonnage 500 and 1000 mln ton) are determined. In the initial state the structure is presented by perlite grains with predominantly lamellar morphology, grains of a ferrite-carbide mixture and structurally free ferrite grains. It is shown that operation of rail steel is accompanied by a complete failure of lamellar pearlite grains in the 15 μm thick surface layer and the formation of a ferrite-carbide mixture with nano-size particles. The strain-induced transformation of steel leads to the increase in the scalar and excessive density of dislocations, the curvature-torsion value of the crystal lattice and the amplitude of internal stress fields.

Biphase Model of Plastic Deformation in Electric Fields

The object of the research is creep deformation proceeding in the conditions of electrostatic field effect. The purpose of the research is to develop the mathematical model of creep under the electrostatic field effect from the positions of representations about the wave nature of plastic deformation process. The theoretical studies of electrostatic field effect being characterized by small (up to ± 1V) potentials on the basis of mass, momentum and energy conservation in two-dimensional formulation were carried out in the process of research. The material being deformed was represented as two phase heterogeneous medium. The first component is excited and being responsible for structure transformation, the second one is unexcited and disconnected with them. For each of the components the laws of mass and momentum conservation were written. For electric fields the Maxwell equations were written. For the first time the two phase filtration model of creep was developed as a result of the research. The model takes into account the inhomogeneity of plastic deformation under electrostatic field effect. The dispersion relation for the waves of plasticity is obtained.

Physical Nature of Structure and Properties Degradation of Rail Surface after Long Term Operation

By methods of optical, scanning and transmission electron diffraction microscopy and microhardness and tribology parameters measurement the changes regularities of structure-phase states, defect substructure of rails surface after the long term operation (passed tonnage of gross weight 500 and 1000 mln. tons) were established. It is shown that the wear rate increases in 3 and 3.4 times after passed tonnage of gross weight 500 and 1000 mln. tons, accordingly, and the friction coefficient decreases in 1.4 and 1.1 times. The cementite plates are destroying absolutely and cementite particles of around form with the sizes 10-50 nm are forming after passed tonnage 500 mln tons. The appearance of dynamical recrystallization initial stages is marked after the passed tonnage 1000 mln tons. It is shown that the operation of steel rails is accompanied by full fractures in surface layers with lamellar pearlite grains and the formation of ferrite–carbide mixtures with nanosized particles. The deformation of steel increases the densities of scalar and excess dislocations, the curvature–torsion values of the crystal lattice, and the amplitudes of internal stress fields. The possible mechanisms of established regularities are discussed. It is noted that two competitive processes can take place during rails long term operation: 1. Process of cutting of cementite particles followed by their carrying out into the volume of ferrite grains or plates (in the structure of pearlite). 2. Process of cutting, the subsequent dissolution of cementite particles, transition of carbon atoms to dislocations (into Cottrell atmospheres), transition of carbon atoms by dislocations into volume of ferrite grains or plates followed by repeat formation of nanosize cementite particles.

Mathematical model of mass transfer at electron beam treatment

The paper proposes a model of convective mass transfer at electron beam treatment with beams in titanium alloys subjected to electro-explosion alloying by titanium diboride powder. The proposed model is based on the concept that treatment with concentrated flows of energy results in the initiation of vortices in the melted layer. The formation mechanism of these vortices rooted in the idea that the availability of temperature drop leads to the initiation of the thermo-capillary convection. For the melted layer of metal the equations of the convective heat transfer and boundary conditions in terms of the evaporated material are written. The finite element solution of these equations showed that electron-beam treatment results in the formation of multi-vortex structure that in developing captures all new areas of material. It leads to the fact that the strengthening particles are observed at the depth increasing many times the depth of their penetration according to the diffusion mechanism. The distribution...

Physical nature of surface structure degradation in long term operated rails

Here we present research data on the structural-phase state and surface properties of rails after long-term operation with a transported tonnage of gross weight 500 and 1000 mln tons. Using optical, scanning, and transmission electron diffraction microscopy, and measurements of microhardness and tribological parameters, it is shown that the wear rate of the material after transport of 500 and 1000 mln tons increases 3 and 3.4 times, respectively, and the friction coefficient decreases 1.4 and 1.1 times. After transport of 500 mln tons, complete failure of cementite plates occurs resulting in round cementite particles of size 10–50 nm. After transport of 1000 mln tons, dynamic recrystallization develops in the material. Two competitive mechanisms are suggested for such evolution: (1) decomposition of cementite particles with their transfer to the volume of ferrite grains or plates in pearlite and (2) decomposition and dissolution of cementite particles, transition of carbon atoms to dislocations (to Cottre...

Intense Pulsed Electron Beam Modification of Surface Layer Facing Formed on Hardox 450 Steel by Electrocontact Method

Using methods of modern material science the structure-phase states and tribology properties of coating surfaced on martensite low carbon Hardox 450 steel by powder Fe-C-Ni-B wire and modified by following electron-beam treatment are studied. It is shown that electron-beam treatment of layer leads to the formation of multiphase state with the main phases: α-phase, iron boride FeB, boron carbide B4C. The surfaced structure formed by intensive electron beam irradiation is characterized by high value of wear resistance. It is in 20 times more that wear resistance of steel and in 11 times more than wear resistance of surfaced layer without of electron beam treatment, friction coefficient decreased in 3.5 and 2.2 times, correspondently.

Structural phase states and properties of the layer surfaced on low-carbon steel with Fe‒C‒Cr‒Nb‒W powder-core wire followed by electron-beam processing

Structural phase states and tribological properties of the coating surfaced onto Hardox 450 martensite low-carbon steel with powder wire Fe‒C‒Cr‒Nb‒W and modified by subsequent electron-beam processing are studied by methods of modern physical material science. It is shown that irradiation of ~5 thick surfaced layer with high intensity pulsed electron beams results in the formation of ~20 μm thick surface layer with the master phases of α-Fe and NbC, Fe3C and M6C(Fe3W3C) carbides. The main difference of the surface layer modified with electron-beam processing from the unmodified volume of the surfacing is the morphology and dimensions of the second phase inclusions. In the modified layer of the surfacing the inclusions have smaller dimensions and are located in the form of interlayers along the grain boundaries. In unmodified surfacing the particles of the faceted shape located chaotically in the grain volume are the basic morphological type of the inclusions. It is noted that the small value of crystal lattice Nb parameter observed in the experiment may be caused by the high level of vacant interstitial sites having the smaller size in comparison with the occupied interstitial sites. It is established that wear resistance of the surfaced layer after electron-beam processing increases more than 70-fold relative to wear resistance of Hardox 450 steel and friction coefficient decreases significantly (~3-fold).

Variation of Strength Characteristics of Titanium Surface Layers Under Magnetic Field Effect

In work using micromechanical test method it is determined that the magnetic field (0.6 T) reduces the mechanical properties of commercially pure titanium and their subsequent stabilization. The dependence of the microhardness on the time of the magnetic field treatment is established. We define a linear dependence of the microhardness on the processing time for the value of the induction of the magnetic field of 0.3 Tesla. Magnetic influence with the induction of 0.4 T is characterized by the exponential dependence of the microhardness on the processing time. Established threshold value holding time of 0.5 hour, below which the effect is observed irrespective of the influence of the magnetic field of the magnetic induction. The hypothesis of a magnetic field on the mechanical properties of the surface layers of commercially pure titanium, which qualitatively explains the observed dependence.