Steel Counterbody Research Articles

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

Influence of the Sliding Velocity on the Wear Intensity of the Sintered Hybrid Composite (Al–12Si)–40Sn upon Dry Friction

Tribological tests of a hybrid composite (Al–12Si)–40Sn prepared by sintering mixtures of powders of silumin and pure tin were carried out using the pin-on-disk scheme. It has been established that an increase in the sliding velocity decreases the wear intensity of the composite upon dry friction, while an increase of the load leads to the opposite result. The data obtained indicate that the main contribution to the wear of the composite comes from the delamination of strongly deformed subsurface layers of the material. With an increase in the sliding velocity, the mechanism of the wear does not change, but, because of the heat-induced softening of the material, wear particles of the steel counterbody are pressed into it that “plate” the surface of the sample and reduce its wear intensity.

Improving the oscillating wear response of cold sprayed Ti-6Al-4V coatings through a heat treatment

Cold spray (CS) coating technique is being studied as a potential solution for repairing aircraft Ti-6Al-4V components. This work is focused on the restoration of damaged components due to wear induced by vibrations. It is known that Ti-6Al-4V CS deposition shows difficulties to obtain non-porous coatings due to the high strength of this material, that is detrimental for wear resistance. In this sense, performing a post-heat treatment leads to lower porosity CS Ti-6Al-4V coatings and improves their mechanical properties, and thus, a better tribological behaviour is also expected. Therefore, the objective of this study was to determine the effect of a post-heat treatment on the wear resistance of Ti-6Al-4V coatings deposited by the CS technique. Ti-6Al-4V CS coatings were used, which have been sprayed with nitrogen as process gas at a temperature of 1100 °C and a pressure of 50 bar. The coatings were subjected to a solution heat treatment followed by a precipitation heat treatment. Oscillating and unidirectional sliding wear experiments were conducted on the coatings at room temperature and at 450 °C. A pin on disc configuration was used with a bearing steel counterbody. The results were compared to those obtained on the substrate (which represents the material to be repaired) and on the as-sprayed coating, which were derived from a previous work. The heat treated coating presented improved wear behaviour as compared to the substrate as well as to the as-sprayed coating, particularly during the high temperature tests. Wear at high temperature was dominated by material transference from the counterbody to the Ti-6Al-4V coating.

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.

Reactive Pulsed Laser Deposition of Clustered-Type MoSx (x ~ 2, 3, and 4) Films and Their Solid Lubricant Properties at Low Temperature.

We studied the tribological properties of amorphous molybdenum sulfide (MoSx) thin-film coatings during sliding friction in an oxidizing environment at a low temperature (−100 °C). To obtain films with different sulfur contents (x ~ 2, 3, and 4), we used reactive pulsed laser deposition, where laser ablation of the Mo target was performed in H2S at various pressures. The lowest coefficient of friction (0.08) was observed during tribo-testing of the MoS3 coating. This coating had good ductility and low wear; the wear of a steel counterbody was minimal. The MoS2 coating had the best wear resistance, due to the tribo-film adhering well to the coating in the wear track. Tribo-modification of the MoS2 coating, however, caused a higher coefficient of friction (0.16) and the most intensive wear of the counterbody. The MoS4 coating had inferior tribological properties. This study explored the mechanisms of possible tribo-chemical changes and structural rearrangements in MoSx coatings upon contact with a counterbody when exposed to oxygen and water. The properties of the tribo-film and the efficiency of its transfer onto the coating and/or the counterbody largely depended on local atomic packing of the nanoclusters that formed the structure of the amorphous MoSx films.

Tribochemical Interaction of Multicomponent Aluminum Alloys During Sliding Friction with Steel

In this work, aluminum multicomponent alloys were studied after friction with steel in a mixed lubrication regime. The resulting secondary structures on the friction surface were investigated by scanning electron microscopy (SEM), energy dispersive analysis (EDX), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction analysis (XRD). In addition to the mass transfer of steel counterbody particles, phase transformations and new chemical compounds formed as a result of interaction with the lubricant were revealed. The release of elements, mainly magnesium and to a lesser extent zinc, from a solid solution of aluminum alloy was also observed, which indicates the occurrence of a non-spontaneous reaction with a negative entropy production.

Characteristics of dry sliding electric contact of sintered metal based composites at catastrophic wear onset

Dry sliding of powder metal based composites was carried out against steel counterbody under electric current of density higher 100 A/cm2. It was shown that the surface layers were transformed into tribolayers under these sliding conditions. An optical image of the possible deterioration of the tribolayer and a method for estimation its specific electrical resistance were presented. It was established by X-ray phase analysis that the tribolayers contained the initial phases and, sometimes, FeO. The relatively low electrical resistance of the tribolayer and the formation of FeO on the sliding surface corresponded to low wear of the composite without alloying metals in the primary structure. The tribolayers of composites with dissolved metals in the primary structure had high specific resistance, were not able to form FeO on their sliding surfaces and had strong deteriorations. This manifested itself as high wear. At the same time a manifestation of low electrical conductivity of the contact was observed. The catastrophic wear of both types of composites began at nearly equal power on the contact spots but at different current densities. It was concluded that the high wear was due to the absence of FeO on the sliding surface and weak relaxation of stresses in the friction zone of composites containing dissolved metals in their base.

The Influence of the Roughness of a Steel Counterbody on the Tribological Characteristics of Friction Composites under Friction in Oil

The influence of surface roughness of a steel counterbody on friction (coefficients of static and dynamic friction) and wear parameters is investigated for friction composite materials that operate in a transmission oil medium. The wear rate of composites and the level of dynamic instability of tribological conjugations (chatter, vibration, and noise) are shown to exhibit a non-monotonic dependence on the roughness of a steel counterbody with a common local minimum, which is typical of various friction materials. A rapid diagnostic method of tribotechnical and NVH-testing of friction materials intended for operation in oil is proposed as well.

Abrasive Wear of a Steel Counterbody in Frictional Contact with Pressed Modified Wood

The article presents results of studying how an abrasive affects the wear of pressed modified wood and steel samples—counterbodies without hardening and with hardening by annealing and application of a diamond-like coating of titanium nitride. It is shown that the (linear and mass) wear rate of unreinforced steel samples is more than 20 times higher than for hardened samples; surface hardening via vacuum coating deposition is ineffective due to its intense peeling in the presence of an abrasive.

Interaction of tungsten in dry sliding against steel under high density electric current

The possibility of creating a wear-resistant dry sliding electrical contact tungsten/steel was studied. It was shown that tungsten caused severe wear of the quenched steel counterbody due to unlimited plastic flow of its surface layer at a current density up to 150 A/cm2 . This indicated the impossibility of achieving satisfactory characteristics of such a contact. Low electrical conductivity and wear resistance of the contact tungsten/steel were presented in comparison with the known high copper/steel contact characteristics under the same conditions. X-ray phase analysis data of the steel sliding surfaces made it possible to state that the cause of the unsatisfactory sliding of tungsten was the absence of the necessary concentration of FeO oxide on the sliding surface of the steel.

Modification of magnetron sputter deposition of nc-WC/a-C(:H) coatings with an additional RF discharge

It is known that the degree of ionization of the coating precursors is one of the key factors in a control of the structure and properties of sputter deposited carbon-based coatings. Numerous modifications of a conventional magnetron sputtering technique were elaborated in order to increase the degree of plasma ionization. The most effective of them were based on an application of an additional source of plasma excitation, independent of magnetron discharge. This paper presents results of the investigations of nc-WC/a-C(:H) coatings, deposited by means of magnetron sputtering of graphite and tungsten targets, enhanced by an additional radio-frequency discharge of a maximum power of 150 W, limited to a volume directly adjacent to the specimens. In order to assess thickness, surface morphology and chemical composition of the coatings, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) techniques were used, while Raman Shift Spectroscopy (RSS) together with XPS was applied to determine the types of bonds between carbon atoms. Tribological properties of the coatings were investigated using a ‘pin-on-disc’ method, with the friction couple comprising bearing steel counterbody. It has been found that additional RF discharge has a significant effect on the type of bonds of carbon atoms in the coating. In the case of non‑hydrogenated nc-WC/a-C coatings, an introduction of additional RF discharge caused an increase of a contribution of sp3 hybridized carbon atoms by 32%, as well as an increase of friction coefficient. The highest share of sp3 hybridization was obtained in the case of hydrogenated nc-WC/a-C:H coatings deposited in Ar + CH4 atmosphere with an enhancement of additional RF discharge maintained at 150 W of power. These conditions brought about a decreased friction coefficient (to a value of 0.05) and a decreased wear rate (to an approximate value of 10−17 m3 N−1 m−1).

INFLUENCE OF DIHYDROQUERCETIN ON FRICTION OF SUPER-HIGH-MOLECULAR POLYETHYLENE BY STEEL AND ALLOY Ti6Al

The main reasons reducing the lifetime and failure of implants are tribo-oxidative processes. Stabilizing additives are used to inhibit tribo-oxidative activity and increase the lifetime of the implant. The most common stabilizer is α-tocopherol. The biocompatible stabilizer of a number of flavonoids, dihydroquercetin, was selected as the thermo- and tribo-oxidative stabilizer of UHMWPE. Dihydroquercetin (DHQ) stabilizes peroxide radicals formed as a result of the tribological process (friction of UHMWPE) by detaching a hydrogen atom from OH groups with the formation of a non-reactive phenoxyl radical. A comparative analysis of the samples, stabilized with DHQ and α-tocopherol, was carried out. The samples studied were prepared by direct compression molding at a temperature of 190ºС. The comparative study of thermo- and tribo-oxidative stability of UHMWPE samples modified with DHQ and α-tocopherol evidences that the thermo-oxidative stability induced with DHQ is higher that of α-tocopherol. In the first case the thermal-oxidative stability of the composition is maintained up to a temperature of 230 °C. Evolution of friction compositions at temperatures higher than that of the human body was investigated. Such tests were conducted using a gradual increase in friction velocity. During the tests, an increase in weight of initial UHMWPE and the composition with α-tocopherol induced by tribo-oxidative processes was observed. The introduction of dihydroquercetin, a highly effective biostabilizer of thermal oxidation, leads to the conservation of the original weight of the samples. When selecting a counterbody for the developed composition with DHQ, a study was conducted of friction on steel 3X13 and Ti6Al alloy used in medicine and in endoprostheses of artificial joints. It was found that the best results are obtained in the case of using a steel counterbody.

Распределение температуры по оси стального образца при скольжении с токосъёмом по стальному контртелу

Распределение температуры по оси стального образца при скольжении с токосъёмом по стальному контртелу

Heat-treatment and mechanical properties of cold-sprayed high strength Al alloys from satellited feedstocks

In prior work, the authors demonstrated a method for the creation of composite coatings containing TiC particles in a pure Al matrix by cold spray via a satelliting technique. Here, the authors investigate the effects of using the ‘Satelliting’ technique on the deposition and characteristics of A6061-TiC coatings fabricated by cold-spray. The results showed clear improvements in the deposition efficiency and porosity of the satellited powder obtained by using the satellited feedstock. Annealing heat-treatment was then applied for further enhancement of the coating's density and wear properties. The heat-treated coating exhibited a ~70% reduction in interlamellar porosity. Dry sliding wear testing using a steel counter body at 5 N showed that using a satellited feedstock with TiC yielded a 55% and 20% reduction in coating specific wear rate in comparison to coatings made using pure 6061 and blended 6061-TiC, respectively. This was further reduced by ~70% and 40% in comparison to the 6061 and blended 6061-TiC coating after heat-treatment with good repeatability.

CHARACTERISTICS OF DRY SLIDING ELECTRIC CONTACT OF METALS IN CONDITIONS OF CATASTROPHIC WEARING

The authors have studied the relation between wear intensity, average contact temperature and phase composition of the surface layers ofAISI 1020 steel, copper and NiTi alloy in dry sliding against the steel counterbody under electric current of density higher than 100 A/cm2 . These contact characteristics are considered carefully at the beginning of catastrophic wear, when the surface layers transit to the utmost state. It was noted that relaxation of stresses in the surface layers was due to the structural transformation in normal wear regime. It leads to tribolayers formation. The high strength of the copper tribolayer is first of all due to the formation of FeO oxide on the sliding surface, which prevents adhesion in contact. In addition, signs of a liquid phase were observed on the copper contact surface. It promoted the low rate of formation and accumulation of structural defects. Emergence of areas of melt and FeO oxide on the sliding surface provides high contact wear resistance. These factors, combined with the high thermal copper conductivity, have caused the tribolayer transition to the limit state at high current density and low contact temperature. The absence of oxides on the sliding surface of the NiTi alloy has caused strong adhesion in the contact, high rate of formation and accumulation of structural defects. Therefore, the tribolayer quickly deteriorates and high wear intensity and rapid increase in the contact temperature are observed with current density increase. Therefore, the catastrophic wear of the NiTi alloy begins at a temperature about 350 °C and at low current density. The sliding surface of AISI 1020 steel contained FeO oxide, therefore strong adhesion is not manifested. Formation of FCC-Fe in tribolayer of AISI steel 1020 is detected, that promotes its accelerated deterioration. Therefore, the tribolayer of AISI steel 1020 transites to the utmost state at a relatively low current density and at a higher temperature. The presented contact temperatures corresponding to the beginning stages of the utmost state of the tribolayer do not exceed 350 °С. Comparison of these temperatures with the known contact temperatures of other metals made it possible to assert that raising of the contact temperature of any metal higher than 400 °С leads to its utmost state. Therefore the characteristics of metals contact at temperatures of sliding contact higher than 500 °С is not of practical interest.

Wear, vibration and acoustic emission characterization of sliding friction processes of coarse-grained and ultrafine-grained copper

Microstructural evolution of copper samples after equal channel angular pressing (ECAP) have been studied. The equiaxed ultrafine-grains first appeared after 4 ECAP passes and then occupied the bulk of the sample after 8 and 12 passes thus forming more homogeneous grain-subgrain structures. High values of ultimate tensile strength 653 MPa and microhardness (180 HV) have been achieved. Tribological testing under unlubricated sliding friction of as-annealed and ECAPed copper samples against a steel counterbody have been carried out with simultaneous registration of vibration acceleration (VA) and acoustic emission (AE) signals. Wear reduced with the ECAP pass number changed from 0 to 12. Structural evolution of metal in different structural states after sliding tests has been studied and its effect on wear and friction has been revealed. The ECAPed samples formed thick oxidized layers on their worn surfaces which then deteriorated by subsurface fracture. This subsurface cracking changed the sliding friction dynamics as well as the AE signal parameters. Correlations between the tribological system vibrations and AE signal parameters have been established.

Secondary Structures as Self-Organization Processes and Finishing Treatment of Friction Surfaces of Slide Bearings and Shafts

The article is devoted to the problem of replacing bronzes with cheaper aluminum alloys for slide bearings. The processes taking place on friction surface of both the aluminum alloy and steel counterbody are observed. The changes occurring during friction were investigated by scanning electron microscopy and energy-dispersive analysis. It has been revealed that secondary structures are formed on the surface during friction process and include all the chemical elements of the tribosystem which is a consequence of its self-organization. These structures are thin metal-polymer films containing mainly carbon and oxygen. Variety and content of alloying components is important as it defines the freedom degrees for self-organization.

The Influence of Secondary Structures on Wear Resistance of Experimental Aluminum Alloys for Monometallic Slide Bearings

The changes occurring on the surface of an experimental high-alloyed aluminum after friction with a steel counterbody have been investigated. The friction surface of the aluminum alloy has been studied by means of scanning electron microscopy and modification of elementary composition on it has been analyzed by energy-dispersive analysis. It has been revealed that secondary structures are formed on the surface during friction process and include all the chemical elements of the tribosystem which is a consequence of its self-organization. The influence of some chemical elements on tribotechnical characteristics of the alloy has been evaluated.

Mechanisms Involved in the Formation of Secondary Structures on the Friction Surface of Experimental Aluminum Alloys for Monometallic Journal Bearings

The processes taking place on the friction surface of high-alloyed aluminum alloys working with steel whilst replacing bronze journal bearings with aluminum are investigated. In this regard, eight experimental aluminum alloys with an Sn content from 5.4% to 11.0%, which also included Pb, Zn, Si, Mg, and Cu, were cast. The surface and subsurface layer of experimental aluminum bearings were studied before and after tribological tests with a 38HN3MA steel counterbody by scanning electron microscopy including energy-dispersive analysis. The best aluminum alloy, which had an Sn content of 5.8% after the friction tests, showed 6.5-times better wear resistance and steel counterbody wear rate than the bronze reference. Both structural and compositional changes in the surface layer were observed. It was revealed that secondary structures formed on the surface during the friction process and included all of the chemical elements in the tribosystem, which is a consequence of its self-organization. Generally, the secondary structures are thin metal-polymer films generated as a result of the high carbon and oxygen content. The interaction behavior of some of the chemical elements in the tribosystem is shown and discussed. In addition, the influence that Sn, Pb, Cu, and C content in the secondary structures has on the tribological properties of low-tin and medium-tin alloys is shown.

Impact of the Structure on Mechanical and Tribological Properties of Sintered (Al–12 Si)–40 Sn Alloy

Interaction of the structure of the composite alloy (Al–12 Si)–40 Sn with its mechanical and tribological properties was studied. The alloy was obtained by the liquid-phase sintering of powder briquettes made of the powder mix of tin PO-2 and an atomized aluminum alloy of the eutectic composition Al–12 Si. Sintering was carried out at a temperature below the melting point of the eutectic; otherwise, the sample melted and lost its shape. It was found that the given sintering temperature does not make it possible to obtain samples with high density; their residual porosity was 6–8% and it almost was not decreased with the increase in the sintering time. The obtained material had low mechanical properties, which slightly improved with the increase in the sintering time to two hours. At the same time, the amount of exuded and evaporated tin noticeably increased. Taking into account the undesirable phenomena that occurred during a long exposure of sintered samples at high temperature, the hot densification was carried out after the short-term sintering. Densification of the sintered samples aiming at removal of the residual porosity was carried out in a closed mold under pressure above the ultimate strength of the alloy. It was established that such operation contributed both to significant improvement of strength and ductility of the studied material. In addition, the obtained nonporous material had high wear resistance under dry friction against a steel counterbody; it was especially noticeable during friction under high pressure. The wear rate of samples with a matrix made of the aluminum-silicon alloy was 30% lower as compared with the alloy with the matrix made of pure aluminum at all other conditions being equal.