Contact Surface Layer Research Articles

АНАЛИЗ СОВРЕМЕННЫХ ЛАЗЕРНЫХ МЕТОДОВ УПРОЧНЕНИЯ ДЕТАЛЕЙ МАШИН И ИНСТРУМЕНТА

The article offers a retrospective analysis of the development of laser and combined lasers based on the use of laser radiation methods of hardening the responsible parts of machines and tools. It is shown that the combination of laser radiation and other advanced technological methods creates contact surface layers of machine with unique physical-mechanical and operational properties forming is the current and promising direction in an improving technologies for their application with high physical and mechanical properties of responsible parts.

АНАЛИЗ РАЗВИТИЯ КОМБИНИРОВАННЫХ ЭЛЕКТРОФИЗИЧЕСКИХ МЕТОДОВ УПРОЧНЕНИЯ ДЕТАЛЕЙ МАШИН И ИНСТРУМЕНТА

The article proposes an analysis of the development of combined electrophysical methods of hardening machine parts and tools based on the use of radiation (laser, electro-beam, ultrasonic, etc.) processing and electromagnetic fields. It is shown that the current and promising direction in improving the performance of the contact surface layers of machine parts, creating high-performance coatings (as well as technologies for their application) with high physical and mechanical properties of responsible parts is the combination of high-energy (laser, electronic, etc.) radiation and electromagnetic fields as a technological factor, as well as other sources of technological energy, which are advanced electrophysical methods of forming working surfaces of mechanical parts of mechanical and mechanical components.

Mathematical simulation of cutting force during grinding using theory of Markov processes

The article presents a cutting force mathematical model which takes into account the grinding wheel working surface wear resulting from abrasion and chipping of grain vertices, pulling of grains out of the wheel bond depending on the grinding time. Wear of grain vertices is considered as a Markov process with discrete time and state, and the process of forming the grinding wheel working surface as a superposition of such Markov processes. The model allows to determine the nature of cutting force distribution in the grinding zone across the contact surface layers of the abrasive tool and the characteristics of changes in the distribution throughout the grinding period. The mathematical model takes into account the influence of the following factors: characteristics of the abrasive tool, the grinding mode, the material to be processed, the initial distribution of grains on the abrasive tool working surface and the strength of their retention. The model includes the probabilities for types of grain vertice wear resulting from abrasion and chipping, pulling of grains out of the abrasive tool bond. The wear type probability calculation is determined by taking into account the actual cutting force of the grain vertex. A change in the grain vertex position resulting from various types of wear after each interaction with the processed material is determined by transition probabilities.

A robust and contact preserving flux splitting scheme for compressible flows

Low-dissipation shock-capturing methods usually suffer from various forms of shock instabilities, such as the notorious carbuncle phenomenon, in simulations of hypersonic flows. Many strategies for tackling the shock instability of flux difference splitting schemes, such as HLLC and Roe schemes, have been proposed while little work has been undertaken on the shock instability of flux splitting schemes. In this paper, we are concerned with the shock instability of a convection-pressure flux splitting scheme. By means of a linearized perturbation analysis, it shows that all of the perturbations in the streamwise direction are damped, while the perturbations of density and shear velocity in the transverse direction are undamped. Due to the special symmetry, the two-dimensional Sedov blast wave problem is studied to demonstrate the relation between the transverse flux and shock instability. Based on the theoretical analyses, a shock stable flux splitting scheme is presented through introducing additional viscosities of entropy wave and shear wave to damp out all perturbations in the transverse direction. For restoring the contact surface and shear layer, a pressure-based function depending on the shock-wave strength is defined to control the amount and location of additional viscosities. Numerical results of several challenging test problems demonstrate that the new scheme has greatly improved the robustness without undermining the accuracy.

Modification of contact surfaces of steel based materials in dry sliding under electric current of high density

The purpose of the work was to study the interrelation of primary structure and wear resistance as well as to receive the initial ideas on contact features and surface layer deterioration in dry sliding against steel under electric current. The tribological behaviour of bearing steel and Hadfield steel (13% Mn) as well as the behaviour of composites on their bases was studied under electric current of high-density. Using X-ray phase analysis it was shown that the electrical current caused a modification of the surface layer of bearing steel and bearing steel sintered composite due to the formation of tribolayer and sliding surface melting in dry sliding against quenched AISI steel 1045. The formation of FeO in the tribolayer was observed also. This contributed to hardening of the sliding surface and to the realization of low wear intensity. Hadfield steel and a sintered composite based on it were capable of forming a tribolayer, where there was a low content of FeO on the sliding surface. This led to a high wear rate due to adhesion. The low thermal conductivity of Hadfield steel based materials should be considered as another reason for the rapid deterioration of their tribolayers.

DEVELOPMENT OF TECHNOLOGY OF SELF-ORGANIZING NATURAL-PROTECTIVE COATINGS FORMATION IN THE INTERCONNECTION AREA OF FRICTION PAIRS IN THE PROCESS OF CUTTING

As a result of scientific and experimental research by modeling the cutting process as a controlled thermodynamic system, the essence of self-organizing new submicrostructures on thin contact surface layers of the tool is revealed. A technological method has been developed for the formation of an intercontact natural protective “white” layer.Investigated the formation mechanism of a “white” layer – a new composite material in the inter-contact space, plays the role of a protective coating, which is explained as a result of existing plastic deformations, normal and tangential stresses, high dislocation density and temperatures in thin surface layers of materials in contact pairs – a cutter-descending chip as well as diffusion of alloying elements W, V, Сr, Mo, Co and strengthening carbide and intermetallic particles WC, VC, MoC, (FeCo)7W6, (FeCo)7Mo6 in the intercontact formation, consisting of hindered strongly deformed, cold-worked, amorphized nanoparticles of the processed material from steel 45, attached to the roughness of the front contact surface of tools from high-speed steels R6M5 and B14M7K25.The “white” layer formed in the contact area of the front surface of the instrument plays the role of a heat insulator and a protective coating, preventing direct contact of the outflow of the material being processed with the tool.Experimentally has been established an additional reserve for increasing tool wear resistance by controlling the interaction of crystal lattices and self-organization in the contact space of friction pairs by new structure formations under the influence of normal and tangential stresses, temperatures, plastic deformations and diffusion with the creation of a naturally protective self-organizing “white” layer playing the role of a heat insulator and protective coatings.Determined the regularities of the formation for protective coatings stagnant and “white” layers in the intercontact space of friction pairs during the cutting process, and revealed the mechanism for creating intellectual coatings on the tool contact surfaces, which react to changes in thermodynamic characteristics and which can be used in the cutting process itself.A combined resource-saving technology has been developed to increase the microhardness, strength, wear resistance and service life of the tool from high-speed steels R6M5 and carbon-free high-speed alloys with intermetallic hardening with cutting tools of type В14М7К25 when machining steel 45.

Experimental Investigations on Microshock Waves and Contact Surfaces.

The present work reports on progress in the research of a microshock wave. Because of the lack of a good understanding of the propagation mechanism of the microshock flow system (shock wave, contact surface, and boundary layer), the current work concentrates on measuring microshock flows with special attention paid to the contact surface. A novel setup involving a glass capillary (with a 200 or 300 μm hydraulic diameter D) and a high-speed magnetic valve is applied to generate a shock wave with a maximum initial Mach number of 1.3. The current work applies a laser differential interferometer to perform noncontact measurements of the microshock flow's trajectory, velocity, and density. The current work presents microscale measurements of the shock-contact distance L that solves the problem of calculating the scaling factor Sc=Re×D/(4L) (introduced by Brouillette), which is a parameter characterizing the scaling effects of shock waves. The results show that in contrast to macroscopic shock waves, shock waves at the microscale have a different propagation or attenuation mechanism (key issue of this Letter) which cannot be described by the conventional "leaky piston" model. The main attenuation mechanism of microshock flow may be the ever slower moving contact surface, which drives the shock wave. Different from other measurements using pressure transducers, the current setup for density measurements resolves the whole microshock flow system.

PHYSICO-CHEMICAL INTERACTIONS BETWEEN COMPONENTS OF THE Al/SiO2 SYSTEM IN METALLURGICAL SYNTHETIC PROCESSES OF CASTING PARTICULATE REINFORCED ALUMINUM ALLOYS

The physicochemical interactions between components in the Al/SiO2aluminum matrix compositions under various temperature conditions of processing are studied. The synthesis of aluminum oxide ceramics in aluminum melts for the production of particulate reinforced Al-Si/Al2O3alloys was performed. The addition of dispersed particles of silicon oxide ceramics was carried out by mixing into aluminum melt in a liquid-solid state. At the temperature-time processing of the Al/SiO2compositions, alumina ceramic with a contact surface layer providing spontaneous wetting with liquid aluminum is realized.

Experimental Investigation of Thermal Fatigue Die Casting Dies by Using Response Surface Modelling

Mechanical and thermal sequences impact largely on thermo-mechanical fatigue of dies in a die casting operations. Innovative techniques to optimize the thermo-mechanical conditions of samples are major focus of researchers. This study investigates the typical thermal fatigue in die steel. Die surface initiation and crack propagation were stimulated by thermal and hardness gradients, acting on the contact surface layer. A design of experiments (DOE) was developed to analyze the effect of as-machined surface roughness and die casting parameters on thermal fatigue properties. The experimental data were assessed on a thermo-mechanical fatigue life assessment model, being assisted by response surface methodology (RSM). The eminent valuation was grounded on the crack length, hardness properties and surface roughness due to thermal fatigue. The results were analyzed using analysis of variance method. Parameter optimization was conducted using response surface methodology (RSM). Based on the model, the optimal results of 26.5 μm crack length, 3.114 μm surface roughness, and 306 HV0.5 hardness properties were produced.

Novel processing of Ag-WC electrical contact materials using spark plasma sintering

Ag-WC (60-40wt%) contact materials based on three WC particle size powders were doped with 0.1wt% Ni and processed by an appropriate powder pre-treatment followed by spark plasma sintering (SPS). The contacts produced were already bonded to a copper profile during SPS in order to eliminate additional processing steps. The SPS composites had a more homogeneous microstructure and were tougher and softer than the materials produced by conventional press-sinter-infiltration. The infiltrated contacts had a lower arc-erosion whereas the contacts produced by both processes had a similar contact resistance. The microstructure after switching confirmed that the SPS materials had a porous contact surface layer and were crack-free in contrast to their press-sinter-infiltrated equivalents.

MODELLING OF THE PROCESS OF ELASTIC-PLASTIC DEFORMATION OF A LAYERED METAL COMPOSITION WELDED BY EXPLOSION

Purpose – to adapt the parametric mathematical model of the process of forming of a layered metal shell under pulse deformation based on the finite difference method, as well as to establish and compile the data on the mechanical properties and regularities of their distribution over the thickness of the layered work-piece. Approach A bimetallic work-piece is covered with a spatial Lagrangian mesh X1X2 connected with the middle surface. We use a scheme. The nodal point of the computational grid of each physical element is the point of bringing the corresponding mass equal to the sum of the masses of the bimetal components and applied to the center of gravity of the element. In the nodal points accelerations are determined. All other values are determined in each component. Mass component points are connected by weightless extensible direct links. Findings А methodology for calculation of technological parameters at the pulse deformation of layered compositions providing the plastic deformation of the contact surface layers was developed. On the basis of the finite-difference approximation of the equations modeling the dynamic behavior of the mechanics of a layered work-piece, algorithms for calculation of its kinematics and stress-strained state are proposed. The results of numerical calculations of the distribution of the radial deformation of the bimetallic stamped work-piece obtained by the explosive welding, change of deformation through the thickness of the bimetallic work-piece and distribution of intensity of deformations are shown. Value Developed algorithms and programs for calculation of the dynamic behavior of a multi-layered shell, critical values of the intensities of strain and stresses at which an interlayer destruction takes place are determined.

Analysis of Plastic Strain Varied with Depth on Micro-contact Point under the Thermo-mechanical Coupling

A thermo-mechanical coupling model for a rigid flat plane and an elastic-plastic rough surface based on three-dimensional fractal theory is established. The model considers the elasto-plastic deformation of the rough solid, the interaction between asperities,and the heat flux coupling between the sliding surfaces. By using the finite element method, the frictional sliding process of the rough surface and the flat plane is simulated. The plastic deformation varied with depth on the contact asperity of the rough solid are analyzed. The numerical results from the analysis and simulation show that the equivalent plastic strain on the frictional contact surface layer increases obviously when the relative sliding velocity changes suddenly and the instantaneous flash temperature emerges. On this frictional contact surface layer, through the different contact asperity, the distribution of the plastic deformation varied with the depth is different. The maximum equivalent plastic strain may be located on the contact surface or in some depth under the contact surface. These results are validated by experimental observation results available in the literature. The experimental results are obtained by studying the surface layer deformation photograph of the metal after the dry friction. The plastic deformation on the frictional contact surface layer accumulates during the frictional sliding, which will result in the micro-hole and the crack source around the micro-defects on the contact surface layer.

The structurally changed layer of superabrasive wheel and workpiece contact surfaces as a factor of improving their wear resistance (a Change of Elemental Composition)

The paper addresses the formation of a structurally changed contact surface layer in a superabrasive wheel and workpiece under thermal and plasma actions, which occurs through redistribution of elemental composition in the material subjected to such actions. The change of the elemental composition is shown to have an effect on mechanical characteristics of the contact surfaces and thus makes it possible to find conditions for improving their wear resistance.

Thermo-stress coupling field of friction lining during high-speed slide of wire rope in a mine friction-drive hoist

In order to seek the intrinsic reason for the serious high-speed slide accident in a mine hoist, the thermo-stress coupling field of friction lining was studied during the high-speed slide. First, the helical contact characteristics were analysed. Subsequently, the thermomechanical properties and the dynamic coefficient of linear expansion were studied, and the thermomechanical constitutive relation was obtained. Then, the theoretical model of thermo-stress was established with the consideration of the helical contact characteristics and the thermomechanical constitutive relation. Also, the numerical simulation was performed by the finite element analysis. Finally, the experiment was carried out on a friction tester. It is found that the temperature is the highest at the contact zone II and the friction heat focuses on the contact surface layer. The variation frequency of the stress is 6.98 Hz at 0.5 m/s. Besides, the catastrophe for the strain and coefficient of friction occurs at 3 m/s. The thermo-stress concentration occurs at contact zone II. The experiment results agree with the simulation ones, which validates the theoretical model of thermo-stress.

Quasi-nano wear mechanism under repeated impact contact loading

A new quasi-nano wear mechanism (QNWM) has been proposed in this paper based on the facts of wear curve turning under high energy impact contact loading. Its characteristic is that the wear rate of QNWM is only 1/10-1/3 that of delamination mechanism at the same energy density. The diameters of wear debris and pits on the worn surfaces fall into the quasinanometer scale (about 50–120 nm). The necessary and sufficient conditions, which bring about the QNWM, are: (i) the nanostructure (nano-crystalline + amorphous phase) in impact contact surface layer has formed by the intensive impact strain; (ii) the delamination wear cracking in sub-surface layer must be restrained; (iii) the microcracks of QNWM are produced in amorphous phase of surface nano-structure layer rather than in nano-crystalline.

The Schottky Parameter Test for Combined Diffusion Welded and Sputter Large Area Contacts

For more authentic comparison of Schottky parameters between combined sputter (Ti/Ni/Au) and diffusion welded (DW) Al contact and direct DW Al contact to SiC the forward current-voltage characteristics were measured at the temperature range 293-473 K on full-packed 0.3 cm2 Schottky diodes. Surprising fact was discovered that the temperature behaviour of parameters remains of the same character for both kind of contacts but for the combined sputter- DW samples the values of parameters is much closer in magnitude to sputter contacts. Apparently, chemical treatment before the DW process preserves untouched the contact surface layer formed by annealing of initial sputter metallization of the chips (e.g. Ni2Si, Ti3SiC2), and this layer serves as barrier during diffusion welding. In the second part of the work we give the results on long-term reliability testing where through the SiC Schottky diode with the DW Al contacts during 300 hr has been passed constant forward stabilized current of 100 A/cm2 density. The primary and final values of Uf for DW Schottky contact have not changed during the test.

Influence of process parameters in pulse plasma nitriding of plain carbon steel

Glow discharge nitriding is widely used to improve the mechanical characteristics of steel components. This treatment produces a modified surface layer, consisting of an outer compound zone and an inner diffusion zone. The compound zone (white layer) is the first zone and therefore, is the contact surface layer. It is of particular interest for establishing the exploitation features of engineering components exposed to the wear and corrosion. It is important to analyse the mechanical and tribological features of this layer. With the aim of optimising the nitriding process and gaining an insight for further research, experimental studies of the pulsed plasma nitriding of plain carbon steel grade DIN C45 (AISI C1043) were carried out, using a pulsed direct current glow discharge. The influence of gas composition, temperature, treatment time, duty cycle and frequency on compound layer thickness and microhardness has been investigated. Five experiments were performed. In each experiment, one of the process parameters was varied while the others were kept constant. The characteristics of the nitride surface layers were studied by optical metallography, Vickers microhardness measurement as well as specially modified Calo test method. The results obtained could be useful in optimising of the nitriding process and computer process control.

Microscopic investigation on the origin of wear by surface fatigue in dry sliding

Simple statistics and morphological analysis in conjunction with the general theory of surface fatigue were used to determine the origin(s) of the mechanisms of wear by surface fatigue (SFW) and their progress with time. New mechanisms of crack initiation and propagation that account for the wear particle formation are envisaged. Surface fatigue is mostly controlled by surface cracks that originate from various site types, depending on the nature of the tested material and testing conditions. It is also shown that cracks propagate at depths between 10 and 60 μm, at deeper levels than previously reported. Several competing mechanisms generate cracks at the contact surface layer. Delamination, as a wear process that is based on wear particles generated from subsurface cracks, plays only a minor role in the overall wear that is generated by surface fatigue phenomena.

Stress state of laminar systems formed from shells of revolution with nonrigid layer contact

An approach is developed for determination of the strain state of elastic systems of layered orthotropic shells of revolution with elastic slip layers when the difference in the tangential displacements of the contact-surface layers is proportional to the tangential stress with a coefficient dependent on the arc length of the generatrix. A resolving system of differential equations and the conditions of the mating sections are obtained for the systems. Results are presented for the solution of specific problems.

Spall initiation and propagation due to debris denting

An analytical model has been developed to investigate the effects of dent on spall initiation and propagation in lubricated contacts. The model is based on the damage mechanics concept that the fatigue spall initiation and propagation is due to the accumulated plastic strain process rather than the stress intensity at the tip of the crack. The contact surface layer was divided into small metal matrix (cell) and for each cell a damage law was applied to determine whether the cell is undergoing damage or not. In this model, spall will be formed when a cell is damaged. A dent profile from finite element analysis for a spherical debris denting the contact surface was used in a point EHL model. The pressure and traction profiles were then used to obtain the internal stresses and accumulated plastic strain for each cell. A damage variable was calculated for each cell based on the accumulated plastic strain. When the damage in a cell reaches a certain level, the cell is damaged and is assumed to fall off the contact surface layer, hence, spall is generated. The spall will further modify the contact surface resulting in new pressure and traction profiles. The accumulated plastic strain and damage are calculated again based on which new spalls may be generated. The entire procedure is repeated which allows the spall to propagate. Spall size and growth rate versus cycle number are presented. The results indicate that spall will always initiate at the dent edge.