Irina Komissarova

Thermocapillary model of formation of surface nanostructure in metals at electron beam treatment

The paper presents the thermocapillary model for the formation of nanostructures in surface layers of materials. It is based on Navier-Stokes hydrodynamic equations, the thermal conductivity equation, the state equation and the boundary conditions. A search for the solutions in the form of a progressive wave has been carried out. The dispersion equation has been obtained and analyzed. The dependence of the instability increment on wavelength has been built. The values of the critical wavelength, at which thermocapillary instability for iron and titanium comes, have been obtained. Value comparison of the calculated wavelengths with cell sizes of crystallization has showed a satisfactory agreement.

Change of deformation characteristics and dislocation substructure of nonferrous metals under influence of magnetic field

The objects of the study were polycrystalline copper of M00b grade and commercially pure titanium BT1-0. Microindentation was carried out on the samples of titanium BT1-0 in the initial state, immediately after magnetic field exposure of 0.4 T and after certain time intervals. The defect substructure of cooper samples M00b, subjected to loading to failure in the creep mode under the influence of magnetic field of 0.35 T and without it, was investigated by the methods of electron diffraction microscopy. It was revealed that the effect of magnetic field exposure on commercially pure titanium BT1-0 leads to the decrease in microhardness with the subsequent stabilization during the time that depends on the processing parameters. And the effect of the magnetic field exposure on copper during the process of creeping results in the redistribution of dislocation substructure types. Also, there are changes in quantitative characteristics of dislocation substructures.

Effect of electron beam treatment on structural change in titanium alloy VT-0 at high-cycle fatigue

Changes in the surface of the fractured structure of commercially pure titanium VT1-0 under treatment by low-energy high-current electron beams and the subsequent cycle fatigue to the failure were analyzed by transmission scanning and transmission electron diffraction microscopy. The increase in the fatigue life of samples in 2.2 times after treatment by electron beams was established. An assumption was made that the increase in the fatigue life of titanium, grade VT1-0, was due to the formation of a lamellar substructure conditioned by high-velocity crystallization of the titanium surface layer.

Regularities of varying the dislocation substructure of copper under creep in the magnetic field

The object of the study is polycrystalline copper of M006 brand. The dislocation substructure (DSS), which is formed in copper under the destruction in creep conditions in a magnetic field of 0.35 T, was studied by diffraction electron microscopy. The substructure of the initial state of copper is characterized by the presence of the following DSS types: chaotically distributed dislocations (56%), a cellular substructure of various degrees of perfection (36%), a netlike substructure (5%), a band substructure (3%), dislocation bundles (3%), and broken subboundaries (2%). It is established that the peculiarities in the quantitative ratio of DSS types manifest themselves under destruction in the magnetic field. Notably, the main DSS type near the destruction zone in copper deformed under creep conditions is the subgrain structure. The application of the magnetic field leads to a decrease in the relative content of the subgrain structure in copper by almost a factor of 2. It is shown that the magnetic-field effect retards the transformation rate of the dislocation substructure under creep of copper, which leads to an increase in strength characteristics.

Effect of the magnetic field on the surface morphology of copper upon creep fracture

The fractography of copper destroyed under creep conditions in a magnetic field of 0.35 T is studied by scanning electron microscopy. The qualitative similarity of the fracture surface morphology, formed in the presence of a magnetic field and without it is revealed. It is shown that in the presence of a magnetic field the average sizes of the formed surface relief in a fiber fracture zone are smaller, and in the radial zone they are larger than that in the corresponding zones of the material deformed under normal experimental conditions. It is revealed that exposure to a magnetic field during the creep deformation mode leads to expansion of the pit size range in the fiber area and to its narrowing in the radial zone. It is found that the application of a magnetic field affects the rate of accumulation and annihilation mechanisms of initiation and defect restructuring of the volume and near-surface layer of copper samples.

Metallographic study on eutectic silumin

The elemental and phase composition, the state of the defective substructure of eutectic silumin used for engineering were studied by the methods of scanning and transmission electron microscopy. The findings of the study show that silumin is a multiphase material and comprises, along with phases based on solid solutions of aluminum and silicon, intermetallic compounds of different composition. Particles of silicon and intermetallics have diverse forms and as a consequence they can both reinforce the material or cause microcracks in the process of product operation.

Effect of Electropulsing on the Fatigue Behavior and Change in the Austenite Steel Structure

The tests were carried out to identify the influence of electropulse treatment on austenite steel ((mass %) 0.44С, 16.50Mn, 0.26Cr, 0.08Ni, 0.34Si, 2.74Al, 0.002S, 0.017P, Fe – balance). The fa-tigue life is reported to increase by 1.8 times. Electron microscopic research into the dislocation structure of the steel was conducted under diverse fatigue conditions with the purpose to give rea-sons for the identified effect. The dislocation chaos substructure, reticular and fragmented dislocation substructures were found in the steel in the initial state. Fatiguing leads to the change in the dis-location substructure parameters. The subsequent electropulse treatment furthers transformation of the grain structure since grains arise and grow due to evolving local dynamic recrystallization and partial transformation of the dislocation substructure and occurrence of a great number of microtwins. The increase in the fatigue life is associated with the mentioned above transformations resulting from electropulse treatment of the steel structural state.

Structure and Properties of the Surface Layer of a Wear-Resistant Coating on Martensitic Steel after Electron-Beam Processing

The paper reports electro-contact welding on Hardox 450 steel with С-V-Cr-Nb-W flux-cored wire. Supplementary irradiation by intense pulsed electron beam was carried out to improve mechanical properties. Micro-and nanohardness, Young modulus and tribological parameters of the modified surface were tested mechanically. It is pointed at the significant increase in the friction coefficient because the surface layer fractures and particles of the surfaced layer are involved in the process of friction. Using the methods of optical and scanning microscopy a great number of micro-pores were detected both on the irradiated surface and through the surfaced layer modified by intense pulsed electron beam. It is demonstrated that electron-beam processing of the deposited layer surface is the reason for occurrence of multi-layer structure. According to measurements it was determined that the modified (surface and transition) layers are 0.3 to 0.5 μm on overage. It was also found out that irradiation of the surfaced metal leads to significant refining of structural elements because of ultrahigh speeds of crystallization and further cooling down of the modified layer. The phase composition of the surfaced metal modified by pulsed electron beam is explored. Niobium carbide (NbC) is reported to form in the surface layer.

Mathematical Model of Nanostructure Formation in Binary Alloys at Electron Beam Treatment

The paper presents a thermoconcentration and capillary mathematical model, describing the formation of 10 to 100 nm structures in the surface layers of binary alloys irradiated by low-energy, high-current electron beams of submillisecond duration. The model is studied by the example of “ferrum - carbon” and “titanium – carbon” systems. It comprises Navier-Stokes equation, thermoconductivity and diffusion equations, as well as surface kinematic and dynamic boundary conditions. The effect of electron beam on material is specified as various temperature and concentration gradients. A dispersion equation for thermocapillary waves in nanowavelength range is developed and analyzed with thin layer approximation. The critical wavelength, leading to this instability, is revealed. It is found out that its values are 17.39 nm for Fe-С and 69.7 nm for Ti-C at the depth of penetration ~ 10-5 m. Wavelengths are compared to the dimensions of crystallization cells and structures, which are formed in them. The paper shows that the model provides a rational explanation of registered regularities.

Increase of Fatigue Life of Titanium VT1-0 after Electron Beam Treatment

The processing of commercially pure titanium VT1-0 with high intensity pulsed electron beam was carried out and the mode of irradiation allowing the increase in fatigue life of the material was revealed. Structure investigations of modified layer and fracture surface of commercially pure titanium samples subjected to fatigue multicycle tests were implemented. By methods of scanning electron microscopy the structural transformations responsible for increase in fatigue life of titanium irradiated with high intensity pulsed electron beam were revealed. It was shown that irradiation of commercially pure titanium of grade VT1-0 with high intensity electron beam (25 J/cm2, 150 μs, 3 pulses) resulted in the refinement of grain structure, formation of multilayer structure. Irradiation facilitated the formation of additional structural levels of micro and nanosize range in surface layer.