Papers by Keyword: Surface Layer

Abstract: The article presents physical regularities for the formation of the surface layer microgeometry of the parts while edge cutting machining of steels from the standpoint of the metal temperature strength and the dislocation-energy concept of the metals failure in the process of cutting. It is proposed to employ an approach that contemplates the use of the informative ability of the thermo-emf signal as an integrated index for the thermophysical properties of a workpiece and a tool in mathematical relations as per roughness parameter calculation.

Abstract: The article considers features of a cutting process of stainless and heat-resistant steels and factors that determine difficulties in machining these materials. The mechanism of influence of advanced plastic deformation on the cutting process, wear of the cutting tool and formation of the quality parameters of the surface machined have been analyzed.

Abstract: It has been shown that the plane surface of a stressed solid can become morphologically unstable relative to the perturbations of the electron density. The above instability is referred to as dynamic and evolves under the relaxation mechanism determined by the electron-electron interaction. The development of the dynamic instability is accompanied by the formation of a dynamic pattern differing from that which is formed under elastic-diffusion instability. To describe the dynamic pattern, a method has been proposed which takes into account the dynamic displacements of the atoms caused by a change in the interatomic interaction during the electron density redistribution. The origin of the different types of the pattern earlier observed experimentally on the free surface of the stressed solids has been explained. The dynamic displacements of the atoms have been shown to stimulate the diffusion mass transfer resulting in a change of the value and the sign of the diffusion coefficient.

Abstract: The equipment of oil refineries and other hazardous production facilities operate under high pressures and temperatures. Such operation conditions require continuous control and equipment remaining operation life period assessment. The existing methods of diagnostics are based on probabilistic remaining life assessment and use data regarding wall thickness variation during the operation process. The present article presents the method of accumulated damage assessment and its approximation to the limiting state, based on electromagnetic processes studying by means of eddy current control method. The main purpose of studies was determination of optimal value of input signal frequency, which could the most informative for determination of regularity of electric signal parameters change depending on the level of accumulated damages. Steel grade 09Г2С samples were used as the subject of studies. The samples were exposed to static tension under constant rate and during the process of samples deformation we measured the value of electric signal under three frequencies: 100 Hz, 10 kHz, and 1 MHz Based on the obtained results we prepared output signal voltage-relative elongation dependencies, which showed that accumulation of plastic deformations in metal leads to reduction of signal amplitude. Particularly interesting was dependence under 1 MHz frequency, under which electromagnetic processes occur in subsurface and surface layers. This dependence was of some regular nature, which was described by means of the sinusoidal function. Graph of the obtained function qualitatively describes the experimental dependence. On the basis of obtained results we can make a conclusion that optimal input signal frequency is within megahertz range, under which difference between the sinusoidal function graph and the empirical curve is minimum.

Abstract: One of the main reasons for the limited service life period of the reaction furnace coils is the carburization of the surface layers, which leads to a decrease in the performance characteristics of the pipe material, decrease in plasticity, generation of internal stresses, change in the metal structure. Therefore, monitoring the state of coils surface in order to detect critical parameters of the carburized layer thickness, using non-destructive methods of control is relevant. The results of the distribution of magnetic parameters over the depth of the carburized layer in the fragments of pipes made of steel 20Х25Н20C2, operated under furnace conditions at high temperatures, for 1300, 6000, 8000, 10000 hours are presented in the article. Analysis of the results showed that the magnetic properties are manifested only in the surface layers of the reaction furnace tubes. At the same time, the longer the service life period, the deeper is the layer exercising the magnetic properties and the higher in this layer the values ​of the constant magnetic field intensity. Analysis of magnetic properties distribution in all studied pipe fragments, both from the inner and from the outer side, showed the non-uniformity of the constant magnetic field intensity distribution, while zones of extremely high values ​are observed. The layer-by-layer surface removal in these zones with the determination of the resultant constant magnetic field intensity showed that there are critical values of the carburization depth, after which a sharp increase of this parameter is registered. These results can be used as a method for carburization depth determination, and also used to develop criterion for rejecting coils of reaction furnaces.

Abstract: This paper deals with the problem of stresses in the surface layer of materials after machining. It analyzes residual stresses as one of the factors affecting the state of the surface layer after machining. It describes the methods for measuring residual stresses and evaluates them from the point of view of suitability for industrial practice. A new method of measuring residual stresses in the surface layer of a workpiece for laboratory use has been proposed and experimentally tested. At the end of the article the options for further solutions in this area are proposed.

Abstract: 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.

Abstract: The provision of certain information regarding the surface layer of the equipment parts is one of the critical issues for the modern mechanical engineering. The development of new technologies of protective-strengthening treatment of critical parts surface requires the development of improved methods for surface layer material state assessment as a result of high-energy impact typical for ion-plasmatic, ion-implantation and combined treatment method. Moreover, the peculiarities of industrial mechanical engineering production require the development of simple and efficient methods of surface layer parameters checkout. The application of protective coatings complicates the use of universal method of the parts surface layer parameters assessment. The present article is devoted to the development and studying of a new method for the parts surface layer state assessment after its treatment of various types, including the protective-strengthening technologies and the application of protective coatings. The specific features of the proposed assessment method are its simplicity, reliability, and universality.

Abstract: This paper studies the computing possibilities of estimating the deformation of the surface layer in machining of details with cutting tools of different levels of wear. The calculation results were experimentally compared with the data obtained by the results of a grid distortion analysis in cutting. Results of how deformation intensity evaluation affects the parameters of vibroacoustic signal have also been presented.

Abstract: For deposition of hard coatings is used a source of metal atoms accompanied by high-energy gas atoms. The metal atoms are produced due to sputtering a flat rectangular target in low pressure magnetron discharge. The gas atoms with energy up to 30 keV are produced due to charge exchange collisions of accelerated ions in space charge sheaths near the surfaces of a grid parallel to the target. The ions are extracted from the discharge plasma and accelerated by high-voltage pulses applied to the grid. The metal atoms pass through the grid and deposit on the products. Conjunction of their trajectories with those of gas atoms bombarding the growing coating allows synthesis of the coatings on rotating dielectric products. Mixing by high-energy gas atoms of the coating atoms and atoms of the product material in its surface layer improves the coating adhesion.