Friction Contact Zone Research Articles

Features of Increasing the Wear Resistance of 90CrSi Tool Steel Surface under Various Electrophysical Parameters of Plasma Electrolytic Treatment

The paper investigates the feasibility of plasma electrolytic treatment (PET) of 90CrSi tool steel to enhance hardness and wear resistance. The influence of electrophysical parameters of PET (polarity of the active electrode, chemical-thermal treatment, and polishing modes) on the composition, structure, morphology, and tribological properties of the surface was studied. Tribological tests were carried out under dry friction conditions according to the shaft-bushing scheme with fixation of the friction coefficient and temperature in the friction contact zone, measurements of surface microgeometry parameters, morphological analysis of friction tracks, and weight wear. The formation of a surface hardened to 1110–1120 HV due to the formation of quenched martensite is shown. Features of nitrogen diffusion during anodic PET and cathodic PET were revealed, and diffusion coefficients were calculated. The wear resistance of the surface of 90CrSi steel increased by 5–9 times after anodic PET followed by polishing, by 16 times after cathodic PET, and up to 32 times after subsequent polishing. It is shown that in all cases, the violation of frictional bonds occurs through the plastic displacement of the material, and the wear mechanism is fatigue wear during dry friction and plastic contact.

Tribological properties of matrine in soybean oil as additive

To enhance the oxidation stability and tribological properties of soybean oil, we synthesized a novel environmentally benign, modified soybean oil (MSO) by incorporating matrine into soybean oil under solvent-free conditions. Furthermore, we experimentally investigated the molecular structure and tribological performance of MSO. Results reveal that the long-chain links of the N–H bonds is formed between matrine and soybean oil molecules through electrostatic interaction, rendering MSO with excellent thermal oxidation stability similar to matrine. The average friction coefficient and wear volume of MSO decreased by 40.5% and 76.4%, respectively, compared to soybean oil. Further, MSO exhibits excellent friction-reducing and antiwear properties compared to PAO. Raman and X-ray photoelectron spectroscopy analyses reveal that MSO containing nitrogen heterocycles is more inclined to penetrate the friction contact zone and form a physical adsorption film. Simultaneously, a chemical adsorption film comprising nitrogen-containing metal complexes and iron complexes was formed during the friction reaction.

Preparation of Multifunctional Nano-Molybdenum Disulfide and Its Tribological Properties in Water-Based Cutting Fluids.

In order to meet the advanced requirements of the manufacturing industry, the use of water-based cutting fluids (WCFs) in metal processing is gradually increasing. However, their lubrication performance still needs to be improved considerably. Therefore, new multifunctional molybdenum disulfide nanoparticles (m-MoS2 NPs) were developed to improve the lubricating properties of WCFs. M-MoS2 NPs modified with silver nanoparticles were prepared by an in situ surface modification. The morphology and chemical composition of the m-MoS2 NPs were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Furthermore, the dispersion and bactericidal properties of m-MoS2 NPs with different weight percents in WCFs were also studied experimentally. The effect of m-MoS2 NPs concentration on friction properties and their friction mechanism were investigated in this research. The results revealed that the prepared m-MoS2 NPs were all nanoscale particles with a layered structure. The dispersion and bactericidal properties of m-MoS2 NPs in WCFs were better than those of MoS2 NPs. The best dispersion and bactericidal properties were observed with 1 wt % MoS2 NPs, as well as friction reduction and antiwear properties. During friction, the two friction surfaces were in the boundary lubrication state,and the prepared m-MoS2 NPs entered the friction contact zone along with the WCFs. A friction chemical reaction film rich in MoS2 and Ag NPs was formed on the friction surface to fill and repair the worn surface, exerting a good lubrication effect.

Structure–Phase Transitions in the Friction Contact Zone of High-Nitrogen Chromium–Manganese Austenitic Steel

The influence of contact stresses on the phase and concentration composition of thin surface layers and wear products in the tribological contact zone of high-nitrogen FeMn22Cr18N0.83 steel was studied using Mössbauer spectroscopy, X-ray structural analysis, and electron microscopy. It was shown that contact compressive stresses developing under the conditions of dry sliding friction in the surface layers (20–25 microns) resulted in the strain-induced dissolution of cellular precipitation products (nitrides Cr2N) and increased the average content of nitrogen in austenite. Antiferromagnetic ordering in austenite caused by the precipitation of secondary nitrides with low chromium and nitrogen content was observed in tiny external layers (~0.1 microns) of the friction surface and products of steel adhesive wear. The effect of tension stresses in the friction contact zone on the formation of strain-induced martensite and nitrides with α″-Fe16N2 structures was established in the wear products.

Weak solutions for contact models involving a class of generalized materials

We consider a contact model for a class of generalized materials whose behaviour is described by means of a bipotential. Using the theory of the bipotentials we deliver a weak formulation consisting of a system of three variational inequalities. The unknown is a triple having as components the displacement field, the Cauchy stress tensor and a Lagrange multiplier related to the friction force on the frictional contact zone. We investigate the existence of the weak solutions by using a fixed point theorem for set-valued mappings and a minimization technique.

Improved installation for determining antifriction properties of materials

The paper presents an improved installation and method for determining friction-electro-thermal properties -friction coefficient, temperature, and value of electrostatic charge in the friction contact zone of machine-building composite wear-resistant-antistatic-thermal conducting polymeric materials during interaction with raw cotton. The existing methods and installations working at the frictional influence of polymers and composite materials with raw cotton have been studied. The general disadvantages of existing devices have been revealed, particularly the impossibility of investigating the frictional properties of materials with cotton. Theoretically and experimentally substantiated principle technological scheme of antifriction interaction of polymeric materials with cotton, where the polymeric material under study is represented as a flat disc rotating in a horizontal plane on which surface cotton is pressed along the normal using a piston in a bottomless box having a cylindrical lateral surface, which leads to minimization of lateral pressure. The developed scheme of antifriction interaction allows maximum imitation of working conditions of working elements of real machines. And also, the antifriction and physical-mechanical properties of composite polypropylene and polyethylene materials filled with organomineral ingredients determined by the developed method and improved installation -tribometer are given.

Development of a hardbanding material for drill pipes based on high-manganese steel reinforced with complex carbides

In the present study the new “casing-friendly” hardbanding alloy based on high-manganese steel reinforced with complex carbide particles was developed by combining thermodynamic modelling within the CALPHAD approach and first-principles calculations. The alloy, deposited by flux cored arc welding on a steel substrate, has a composite structure consisting of manganese-austenite with the ability to work hardening, fine (up to 5 µm) inclusions of the multicomponent carbide (Nb, Ti, Mo, V) and C the thin layers of (Mo,V)C at the austenite grain boundaries. The comparative wear tests carried out with commercially available hardfacing materials of the Fe-W-C and Fe-Cr-C systems showed that the proposed alloy has the best combination of properties preventing the wear of the drill casing, while its abrasion resistance as well as wear resistance in sliding friction conditions by steel counterbody is close to hypereutectic high chromium alloys. The microhardness tests performed on deformed specimen areas after the friction tests show the presence of a significant hardness gradient in the range of 800-450 HV at a distance of about 300 µm when moving perpendicularly away from the zone of friction contact. During the microscopic observation of the layer deposited with the developed alloy and the interfaces between the deposit and the base steel no cracks, pores delamination were detected indicating a strong metallurgical bonding. The hardbanding process was performed for drill pipe joints with the worn Fe-based high chromium alloy hardbanding after exploitation, which allows the drill pipe to be reused with the same durability.

Enhancing wear performance by depositing alumina/GNPs coating on textured WC-TiC-Co substrates

Grid and line textures were made on the top surfaces of WC-TiC-Co cemented carbide substrates. Suspension High Velocity Oxy-Fuel (SHVOF) was utilized to deposit alumina and graphene nanoplatelets (GNPs) coating on the textured surfaces. The friction and wear behaviors of the Alumina/GNPs coating were evaluated using dry sliding wear tests against alumina balls. The friction reduction mechanism of alumina/GNPs coating was presented. GNPs in the alumina coatings played a significant role in reducing the coefficient of friction (CoF) up to 40 % and improving the wear resistance properties of the coating. A stress distribution model of the friction contact zone was provided to analyze the tribological performance of the textured sample. The friction reduction mechanism for alumina/GNPs coating was discussed. These results offer a benchmark for further studies combining microtextured surfaces and SHVOF thermal sprayed coatings as promising candidates for high wear resistant applications.

Structural aspects of surface hardening of parts operating under wear conditions

The article describes the processes occurring in the frictional contact zone under real operating conditions. Analyzes the existing material science approaches to the issues of surface destruction during friction. Studies the structural aspects of surface layers that can effectively resist wear. The conditions of structural self-organization of friction surfaces on the meso-, micro- and nanoscale are formulated. Examples of modern technologies that maximally realize hardening mechanisms to increase the wear resistance of steels are given.

Tribocorrosion Performance of Cr/CrN Hybrid Layer as a Coating for Machine Components Used in a Chloride Ions Environment

The aim of the article was to identify the effect of material hardness on the tribocorrosion process by comparing two material solutions. The analysis concerned the assessment of the process intensity and the identification of the mechanisms responsible for material loss. Possible mechanisms of tribocorrosion common for materials of high hardness were determined. Two classic material solutions (based on AISI 1045 steel) ensuring high hardness of the subsurface layers were tested: nitriding with an additional oxidation and impregnation process, and Physical Vapour Deposition (PVD) coating. In order to better identify the impact of hardness on the tribocorrosion process in each individual test, the pressures in the contact zone were increased. The tribocorrosion tests were carried out in 3.5% NaCl with free corrosion potential (OCP) for the ball-on-plate system. The results of the tribocorrosion tests presented in the article indicate that the synergy effect of friction and corrosion can be generated by the same mechanisms of material removal in both the material solutions tested. The intensity of these mechanisms is determined by material hardness. The likely mechanism of generating the synergy effect may be related to the formation of local pits along the friction path. The corrosion processes that are initiated by the cracking of the hard surface layer create local cavities, which most probably intensify frictional wear in successive time intervals. The area around the cavities facilitates plastic deformation, the initiation of cracking of the cyclically deformed layer and the tearing of larger pieces of material (especially at higher unit pressures in the frictional contact zone).

Wear mechanism of medium carbon steel after its plasma electrolytic nitrocarburising

This article considers the change in the tribological characteristics of medium carbon steel after its anodic plasma electrolytic nitrocarburising in a carbamide electrolyte. Phase and elemental composition of the nitrocarburised layer was studied using X-ray analysis and nuclear backscattering of protons. Optical and electron microscopes were used to observe friction tracks. It has been found out that the wear process in nitrocarburised samples is followed by plastic displacement of the metal in the friction contact zone according to the molecular-mechanical and fatigue theory of wear and application of the Kragelsky criterion. It has been shown that an increase in the sliding velocity of 0.5 m/s to 1.5 m/s results in a linear decrease in the friction coefficient from 0.65 to 0.45. The minimum wear rate is achieved after nitrocarburising of steel at 750 °C for 7 min and a sliding speed of (0.4–0.55) m/s. Anodic nitrocarburising increases the wear resistance of steel by 40% compared to quenching at a sliding speed of 0.9 m/s.

Research of Tribotechnical Properties of Composites Based on UHMWPE, Including Friction in the Environment of Various Lubricants

Dependences of the wear resistance of ultra-high molecular weight polyethylene and composites based on it with carbon fibers on contact pressure have been obtained, which make it possible to determine their load capacity in the regime of dry and boundary friction in the environment of various lubricating oils at a sliding speed of a steel counterbody of 0.5 m/s. It has been established that the life of UHMWPE and composites based on it during dry friction with increasing contact pressure is determined mainly not by the wear of the working surface, but by the plastic deformation of the surface layers of the composites due to an increase in temperature in the frictional contact zone. It has been found that the use of gear oil as a lubricant during friction of PCM contributes to the formation of a more durable boundary layer which protects the material from wear

Structural Transformations and Tribological Effects in the Surface Layer of Austenitic Chrome-Nickel Steel Initiated by Nanostructuring and Oxidation

Metallography, electron microscopy, and X-ray diffraction are used to study the effect of preliminary plastic deformation in the friction-contact zone on the structural transformations and wear resistance of 12Cr19N9T austenitic stainless steel subjected to subsequent oxidation in air at temperatures of 300–800°C for 1 h. Severe deformation under dry sliding friction produces a two-phase (γ + α) nanocrystalline structure in a ~10-μm-thick surface layer of the steel. The microhardness is 5.2 GPa. Subsequent oxidation at 300–500°C causes an additional increase in the microhardness of the deformed surface layer of steel to the value of 7.0 GPa. This is due to the active saturation of austenite and deformation-induced α'-martensite with oxygen atoms, which rapidly diffuse deep into the metal along the grain boundaries. The oxygen concentration in the surface layer and steel wear products reaches 8.5 wt %. The atoms of the dissolved oxygen efficiently pin dislocations in the γ- and α' phases, increasing the strength and wear resistance of the surface of the 12Cr19N9T steel. Oxidation at 550–800°C results in the formation of a large number of Fe3O4 (magnetite) nanoparticles, which increase the resistance of the steel to thermal softening and its wear resistance.

Dry Adhesive Friction Process Regularities during Frictional Contact of Heterogeneous “Copper-Aluminum” System Materials

By means of optical and scanning electron microscopy the surface layer structure of aluminum alloy AMg5 samples with introduced copper part after adhesive frictional contact with AISI 420 steel counterbody was studied. It is revealed that under plastic deformation and material fragmentation in the frictional contact zone a complex mixture of different phase layers is formed due to the formation of different flows of aluminum alloy and copper during friction. Mechanical mixing of a material occurs on all length of a friction path with different intensity depending on distance to copper fragment. Both laminar and turbulent flows of material are formed in the surface layer, as well as a wide range of solid solutions, intermetallic phases and mechanical mixtures.

Frictional cohesive zone model for quasi-brittle fracture: Mixed-mode and coupling between cohesive and frictional behaviors

In this study, a general frictional cohesive zone model (FCZM) dedicated to quasi-brittle fracture is proposed to describe the mechanical response of an interface under combined traction or compression and shear loadings. Under combined traction and shear loadings, mixed-mode I+II cohesive zone model, as proposed by Camanho et al. (2003), is used to express the mixed-mode response of the interface and the dependence to the loading path consistent to the one expected in quasi-brittle fracture. Under combined compression and shear loadings, the novelty lies in the proposed coupling between Mode II cohesive behavior and frictional behavior based on the damage level leading to a progressive rising of the frictional stress associated with the softening part of the cohesive behavior of the interface. FCZM thus describes a smooth transition from a cohesive zone to a pure frictional contact zone. Applied to the masonry context, this general FCZM can be fully characterized through two fracture tests carried out on small masonry assemblages. Finally, FCZM is implemented in LMGC90 discrete element code and used to simulate the experimental response of an unilateral cyclic shear test carried out on a triplet of limestone blocks assembled by two mortar joints.

Wear resistance of the surface nanocrystalline structure under an action of diethylene glycol medium

The influence of nanostructurisation of steel produced by mechanical-pulse treatment on wear resistance of the friction pair ring—insert in diethylene glycol medium which used during the process of natural gas drying was studied. The ring of 0.4C–1Cr steel after quenching and tempering at low temperature was subjected to surface treatment for nanostructurisation, and then it was tested as a part of the friction pair with other friction pair component—high strength cast iron. As a reference the pair 0.4C–1Cr steel after quenching and tempering (ring)—bronze (insert) was used. The treatment due to a severe plastic deformation led to the formation of the nanocrystalline structure with a grain size about 20 nm and microhardness 8.6 GPa on specimen surface. High wear resistance of both components of the friction pair steel–cast iron was reached as a result of surface treatment of the steel component, since it significantly reduced friction coefficient and temperature in the friction contact zone.

Effects of structural parameters of oil groove on transmission characteristics of hydro-viscous clutch based on viscosity-temperature property of oil film

PurposeThe purpose of this paper is to study the influence of structural parameters of oil groove (such as central angle number, depth and so on) on pressure, flow, load capacity and transmitted torque between friction pairs of hydro-viscous clutch.Design/methodology/approachAccording to the working process of friction pairs of hydro-viscous clutch, mathematical models of hydrodynamic load capacity and torque transmitted by the oil film were built based on viscosity-temperature property. Then analytical solutions of pressure, flow, load capacity and transmitted torque were obtained; effects of central angle of oil groove zone and friction contact zone, oil film thickness, number of oil grooves on pressure, flow, load capacity and torque were studied theoretically.FindingsThe research found that the central angle of oil groove zone, number of oil grooves and oil groove depth have similar effects on flow, which means that with the increase of central angle, number or depth of oil grooves, the flow also increases; pressure in friction contact zone and oil groove zone drops along radial direction, whereas its value in oil groove zone is higher. With the increase of the central angle of oil groove zone, pressure in friction contact zone and friction contact zone rises, and the load capacity increases, whereas the transmitted torque drops. Number of oil grooves has little effect on load capacity. When the oil film thickness increases, its flow increases accordingly, whereas the pressure, load capacity and transmitted torque drops. Meanwhile, the transmitted torque decreases with the increase of number of oil grooves, whereas the oil groove depth nearly has no effects on transmitted torque.Originality/valueIn this paper, mathematical models of hydrodynamic load capacity and torque transmitted by oil film were built based on viscosity-temperature property in the working process of hydro-viscous clutch, and their analytical solutions were obtained; effects of structural parameters of oil groove on transmission characteristics of hydro-viscous clutch based on viscosity-temperature property were revealed. The research results are of great value to the theory development of hydro-viscous drive technology, the design of high-power hydro-viscous clutch and relative control strategy.

Effect of material state on the wear of filled polytetrafluoroethylene composite F4K20 on its basis

Tests for the wear of polytetrafluoroethylene and composites on its basis with different glass transition and softening temperatures has been performed. It has been demonstrated that a rise in temperature leads to an abrupt rise in wear due to the build up of adhesive on the metallic counterbody. The method of temperature calculations in the frictional contact zone has been developed and tested. It has been demonstrated that the introduction of filler into polytetrafluoroethylene results in a rise in the glass transition temperature from–120°C, which corresponds to polytetrafluoroethylene, to +150°C.

Effective activation energies of chemical reactions and viscous flow of liquids depending on pressure in tribosystems with boundary and mixed friction

This work presents a kinetic analysis of the probable chemical reactions in a frictional contact zone depending on their energetics, temperature, and pressure, as well as the impact of these factors on the viscous flow of liquids, which can be used as an oily base in tribosystems with mixed boundary friction. The dependences of the effective activation energy and viscous flow of liquids on pressure have been analyzed. It has generally been shown that the effective activation energy of thermally activated chemical reactions and viscous flow depends on the activation volume and consists of standard activation energy under standard conditions and additional components connected with the influence of pressure on these processes.

Mechanical behavior of soil-steel structure subjected to live loads and different water conditions

The paper describes the analysis of a three-span soil-steel bridge along the road section crossing a dry anti-flood reservoir. The structure can be occasionally filled with water. The authors investigate internal forces and stresses in the shells due to live loads at different water conditions. Finite element simulations are carried out assuming elasticplastic behavior of soil, elastic shell and nonlinear (frictional) contact zone. The analysis takes into account soil load history. In particular, the construction and operation of the bridge under quasi-static live loads is considered. The construction stage includes laying and compaction of the backfill. Then, the bridge in operation is investigated at three different water conditions: normal use (dry reservoir), maximum water level (flood) and lowering of the water level in the reservoir. The results show that during the flood the maximum stress in the shell significantly increases. Moreover, some of non-linear effects, typical in such structures, e.g. hysteretic effect, become more evident in comparison to normal use of the bridge.