Papers by Keyword: Surface Layer

Abstract: A number of parts of roller-screw mechanisms (RSM), which work in aggressive environments, are made of corrosion-resistant stainless steel 40Cr13 (AISI420 analogue). These elements include a screw and rollers. For these parts, it is necessary to have hard surface layers and a soft core. A promising method for obtaining the necessary requirements is surface laser modification. The article investigated the effect of laser surface treatment on the value of the coefficient of elasticity, hardness, coefficient of friction and the amount of wear of products made of stainless alloy steel 40Cr13. For laser processing, the SVAROG-1-5DR laser complex (Russia) was used. Various modes of surface laser modification were set. For this purpose, the power of the laser power, the speed of movement of the laser beam relative to the treated surface, and the focal length were varied. The Vickers hardness and tribological characteristics were measured using a microcombitester and tribometer manufactured by SSM Instruments SA (Switzerland). The Rockwell hardness was measured using a TN 301 hardness tester manufactured by Time Group (China). The structure of the alloy was studied by metallography and X-ray diffractometry. It was found that the indicators of hardness and wear resistance of the surface layers of sctructural 40Cr13 steel strongly depend on the laser treatment modes. These dependencies are extreme, with highs and lows. The paper presents the quantitative values of the hardness and wear resistance indicators before and after laser treatment of the surface of this steel in various modes. The reasons for the change in the hardness and wear of the surface layers of 40Cr13 steel after laser treatment under different modes are established. The results of the work were used to optimize the modes of laser treatment of the surface of 40Cr13 steel in order to obtain the maximum values of hardness and wear resistance.

Abstract: On the basis of the conducted theoretical and experimental studies, the dependences for determining geometric, physical and mechanical parameters of the surface layer quality, wear resistance and corrosion rate depending on the modes and conditions of electroerosion of machine parts are presented. They allow determining optimal modes and conditions of electroerosion to ensure the required parameters of the surface layer quality (with a two-stage approach it provides design and technological support of operational properties), wear resistance and corrosion rate (with a single-stage approach it makes direct technological support possible).

Abstract: The metal workpiece Surface Layer (SL) Residual Stresses (RS) modeling and computational algorithms creation relevance is shown. The RS forming discrete elastoplastic finite element model at Surface Plastic Deformation (SPD) hardening treatment, including technological inheritance effect, is presented. A model feature is the complex non-monotonic types of metal loading and subsequent unloading and hardened body effect consideration, as well as residual stress tensor components evaluation as a result of these effects. Residual stress tensor components calculations in the workpiece hardened surface layer after treatment with different routines are performed. The metal hardening effect on the residual stresses values and distribution is established. The correlations between the residual stress tensor components and the main treatment routine parameters - the roller tension and profile radius are established.

Abstract: The main purpose of this work is to study and evaluate the mechanical properties of nanocomposite coatings based on metal-ceramics. The research also estimates factors affecting the unique properties of these surface coatings. The study compares the physical and mechanical properties of tool material plates with a nanodispersed multilayer composite coating and analyzes the results of mechanical tests with and without these coverings. The results of the investigation show that nanocomposite coatings contribute to hardness, strength and wear resistance more than three times, while traditional hardening methods, such as thermal and chemical-thermal treatment, improve the mechanical properties much less. It can be concluded that nanocomposite coatings can increase the strength resource of the tool. Their main disadvantage is the individuality of the properties of each coating and the need for expensive equipment for their creation and application. In the use of nanocomposite coatings to increase surface properties, multicomponent coatings are of the greatest interest. As a result of this work, the nanocomposite metal coating of the nc-TiN/a-Si₃N₄ system was studied, the dependence of properties on the content of the nc-TiN and a-Si₃N₄ phases was examined, and the optimal ratio was found which ensured the highest values of hardness with the best wear resistance.

Abstract: The article considers the effect of laser treatment of bearing steel on the change in the elasticity modulus and hardness of the steel SHH15SG. Multi-factor models were obtained that relate the output parameters to the power W of laser radiation, the longitudinal feed Spr of the laser beam and the distance L from the protective glass of the focusing head to the workpiece surface. According to the degree of reduction of the influence on the elastic modulus of steel SHH15SG subjected to laser treatment, these factors are arranged in a sequence: W, Spr, and L. With increasing W and L the modulus of elasticity and hardness of the treated surface layer increase. 3M-XYZ surface-graphs, 3M-XYZ contour-graphs of interactive influence of independent factors on the elastic modulus and hardness of the surface layer are constructed, which simplifies the procedure for assigning the processing mode. The research results are useful for manufacturing and design companies that implement laser technologies and create laser equipment.

Abstract: Technologically, ultrajet mesodiagnostics (UJM) consists of local hydroerosive indentation by ultrajets (UJ) of water on the surface of the analyzed object (OA) and the subsequent study of the results of this minimally invasive microdestructive effect on its surface layer. Obviously, mathematical models’ construction of the functional relationship between the informative-physical signs of hydroerosive UJ destruction and the surface layer’s state parameters of various OA, primarily their defectiveness, is very important for the development of this potentially promising technology for ensuring the quality of critical products, mainly aviation and other industries. In this regard, the work proposes a probabilistic UJM model, which consists of analyzing the kinetics of the formation of an aggregate set of eroded particles, as a process caused by a combination of appropriate necessary and sufficient conditions for its implementation. The former include the topographic features of the microdefectiveness’ characteristics of the surface layer material, and the latter consist of a certain variational-force hydrodynamic effect of the diagnostic UJ on it. This approach made it possible to obtain calculated data related to probabilistic distribution of the UJ-eroded particles’ sizes of hypothetical OA, as a coordinate function describing the microdefects’ concentration in its surface layer. These functions are close to the available results of experimental UJM of typical and promising materials used in the manufacture of machinery technology.

Abstract: Nd-YAG lasers have been successfully used in recent years as reliable heat source to surface modification of engineering materials such as laser surface re-melting. In the present study, X12 tool steel was surface modified by using pulse Nd-YAG laser technique. Laser parameters are selected of 12 J pulse energy, 15 Hz frequency, 20 mm defocus length, 6 ms pulse duration, and 5.6 mm /s mm scanning speed. These parameters were chosen after undertaking trials to give suitable parameters in this process. Optical microscopy and backscattered scanning electron microscopy (SEM) with EDS and X-ray diffraction techniques were used to analyse the microstructure changes of the surface of tool steel. Wear resistance test was achieved by using a pin on disk method. The reason for this work is to improve the wear resistance for surface layer of tool steel after changes the morphology of the structure by rapid solidification during laser re-melting. In general, the structure consists of the dendrite and cellular structures with δ ferrite formed under conditions of rapid solidification without the primary coarse carbides. After laser melting, the results of the structure at the surface layers show an increase in wear resistance.

Abstract: The operational characteristics of metal components are often determined by the status of surface. In mechanical loading of solid bodies, the impact of the surface properties on formation and spreading of surface cracks is obvious, mainly as regards cyclic loading. Therefore, it is important to pay attention to knowledge of surface properties and their improvement.Cold plastic deformation is the easiest way to change the mechanical properties of the materials. The possibility of surface strengthening by ball or roller burnishing was found 80 years ago and since then has spread mainly into engineering and the automotive industry.In the authors’ workplace, experiments for surface layer hardening without ultrasound were realized with a newly developed device where the compressive force was applied statically, not dynamically. In the experimental part, we focused on the status of surface layers, especially the microstructure, hardness and roughness.

Abstract: Hydrogen absorption leads to redistribution of the components of the surface layer of the amorphous alloy Fe_73.8Si_12.7B_9.4Nb_3.2Cu noncontact side, while the amorphous structure of this layer is preserved. The type of the micro-groups Fe_y Si_x changes in such a way that the ratio y: x decreases (to less than 1) and the chemical bond polarity decreases, as well. After degassing, the surface layer composition becomes similar to those before hydrogenation. The loss of the mechanical stability of the amorphous ribbon is accompanied by the formation of the micro-groups Fe_y Si_x with a decreased ratio of y: x.

Abstract: During low-temperature annealing, the segregation of the alloying element leads to a strong enrichment of the surface layer, causing a rearrangement of the surface electron structure. This change in the electron structure is manifested in the characteristic energy loss spectra. Annealing of single crystals at 400–500 K leads to an increase in the density of surface electron states. As shown by the calculations of the surface potential using experimental data on the temperature dependence of the surface concentration, dopant segregation causes a linear increase in the surface potential.