Alexey Moshkovich - Academia.edu (original) (raw)

Papers by Alexey Moshkovich

Research paper thumbnail of Tungsten Disulfide Inorganic Nanotubes Functionalized by PTFE for Friction Application

Tungsten Disulfide Inorganic Nanotubes Functionalized by PTFE for Friction Application, 2021

Inorganic nanotubes (INTs) and fullerene-like nanoparticles (NPs) of WS2/MoS2 penetrate and exfol... more Inorganic nanotubes (INTs) and fullerene-like nanoparticles (NPs) of WS2/MoS2 penetrate and exfoliate at the contact interface and facilitate tribofilm formation. While the tribological properties are greatly improved by exfoliated NPs that shed easily, they may be diminished by agglomeration in oil. Therefore, surface functionalization is employed to improve dispersion in oil-based suspensions. Here, WS2 INTs were functionalized by polytetrafluoroethylene (PTFE) in a simple and cost-effective bath sonication method. WS2-INTs with two concentrations of added PTFE were characterized by scanning and transmission electron microscopy, micro-Raman spectroscopy, and thermogravimetric analysis. Superior distribution of WS2 was observed before and during friction experiments. Chemical analysis showed a significantly greater amount of PTFE-coated INTs on rubbed surfaces, in accordance with the improved friction and wear properties.

Research paper thumbnail of Friction, wear and deformed structure of Ag and Ni under early stages of scratching

Research paper thumbnail of Electrophoretic Deposition of Hydroxyapatite Film Containing Re-Doped MoS2 Nanoparticles

International Journal of Molecular Sciences

Films combining hydroxyapatite (HA) with minute amounts (ca. 1 weight %) of (rhenium doped) fulle... more Films combining hydroxyapatite (HA) with minute amounts (ca. 1 weight %) of (rhenium doped) fullerene-like MoS 2 (IF) nanoparticles were deposited onto porous titanium substrate through electrophoretic process (EPD). The films were analyzed by scanning electron microscopy (SEM), X-ray diffraction and Raman spectroscopy. The SEM analysis showed relatively uniform coatings of the HA + IF on the titanium substrate. Chemical composition analysis using energy dispersive X-ray spectroscopy (EDS) of the coatings revealed the presence of calcium phosphate minerals like hydroxyapatite, as a majority phase. Tribological tests were undertaken showing that the IF nanoparticles endow the HA film very low friction and wear characteristics. Such films could be of interest for various medical technologies. Means for improving the adhesion of the film to the underlying substrate and its fracture toughness, without compromising its biocompatibility are discussed at the end.

Research paper thumbnail of Effect of Stacking-Fault Energy on the Deformed Structures and Work Hardening of Ag and Ni after Scratching during Early Loading Stage

Journal of Materials Engineering and Performance

Research paper thumbnail of Effect of Plastic Deformation and Damage Development during Friction of fcc Metals in the Conditions of Boundary Lubrication

Lubricants

The main goal of the presented work was the analysis of the interaction between deformed microstr... more The main goal of the presented work was the analysis of the interaction between deformed microstructures and friction and the wear properties of four face centered cubic (fcc) metals. Pure fcc metals such as Ag, Cu, Ni, and Al with different values of stacking fault energy (SFE) were chosen for pin-on-disk tests in lubricated conditions. Friction properties of the four fcc metals are presented herein as their Stribeck curves. The transition from elasto-hydrodynamic lubrication (EHL) to boundary lubrication (BL) regions depends mainly on the values of SFE, hardness, and contact temperature. The acoustic emission (AE) parameters were analyzed in the transition from the EHL to the BL region. The models of friction in different lubricant conditions related to the AE waveforms were proposed. The nanocrystalline top surface layers characterized the deformed structure during friction of Ag in the BL region. The lamellar cross-sectional microstructure was formed in the subsurface layers of ...

Research paper thumbnail of Deformation Microstructure and Chemical Composition of Surface Layers of Cu and Al Under Friction in Lubricated Conditions

Research paper thumbnail of Microstructure and nanohardness of Ag and Ni under friction in boundary lubrication

Research paper thumbnail of Testing of WS2 Nanoparticles Functionalized by a Humin-Like Shell as Lubricant Additives

Lubricants

Nanoparticles of transition metal dichalcogenides (TMDC) have been known to reduce friction and w... more Nanoparticles of transition metal dichalcogenides (TMDC) have been known to reduce friction and wear when added to oil-type liquid lubricants. Aggregation limits the ability of the nanoparticles to penetrate into the interface between the two rubbing surfaces-an important factor in friction reduction mechanisms. Doping has been successfully used to reduce agglomeration, but it must be done in the production process of the nanoparticles. The use of surface-functionalized nanoparticles is less common than doping. Nonetheless, it has the potential to reduce agglomeration and thereby improve the reduction of friction and wear. In this study, we present the results of preliminary tribological ball-on-flat tests performed with WS 2 nanoparticles functionalized by a humin-like conformal shell, as additives to polyalphaolefin-4 (PAO-4) oil. We tested WS 2 inorganic nanotubes (INTs) and two grades of inorganic fullerene-like nanoparticles (IFs). The shell/coating was found to improve friction reduction for IFs but not for INTs through better dispersion in the oil. The thicker the coating on the IFs, the less agglomerated they were. Coated industrial-grade IFs were found, by far, to be the best additive for friction reduction. We suggest the combination between reduced agglomeration and poor crystallinity as the reason for this result.

Research paper thumbnail of Electrophoretic Deposition of Hydroxyapatite Film Containing Re-Doped MoS₂ Nanoparticles

International journal of molecular sciences, Jan 26, 2018

Films combining hydroxyapatite (HA) with minute amounts (ca. 1 weight %) of (rhenium doped) fulle... more Films combining hydroxyapatite (HA) with minute amounts (ca. 1 weight %) of (rhenium doped) fullerene-like MoS₂ (IF) nanoparticles were deposited onto porous titanium substrate through electrophoretic process (EPD). The films were analyzed by scanning electron microscopy (SEM), X-ray diffraction and Raman spectroscopy. The SEM analysis showed relatively uniform coatings of the HA + IF on the titanium substrate. Chemical composition analysis using energy dispersive X-ray spectroscopy (EDS) of the coatings revealed the presence of calcium phosphate minerals like hydroxyapatite, as a majority phase. Tribological tests were undertaken showing that the IF nanoparticles endow the HA film very low friction and wear characteristics. Such films could be of interest for various medical technologies. Means for improving the adhesion of the film to the underlying substrate and its fracture toughness, without compromising its biocompatibility are discussed at the end.

Research paper thumbnail of Study of the transition from EHL to BL regions under friction of Ag and Ni. I. Analysis of acoustic emission

Tribology International, 2017

Research paper thumbnail of Alleviating fatigue and failure of NiTi endodontic files by a coating containing inorganic fullerene-like WS2 nanoparticles

Journal of Materials Research, May 27, 2011

Nickel-titanium (NiTi) alloys combine several remarkable characteristics, among them are shapemem... more Nickel-titanium (NiTi) alloys combine several remarkable characteristics, among them are shapememory, superelasticity, great strain recovery, good biocompatibility, and corrosion resistance. These render them well suited to a wide range of medical applications, such as cardiovascular stents, laparoscopy, and dental applications such as NiTi endodontic files (EFs) used for root canal treatment, which are the focus of this work. Unfortunately, fatigue-induced and incidental failure of NiTi EFs is not uncommon, which may lead to severe medical consequences. Here we examine the effects of cobalt coatings with impregnated fullerene-like WS 2 nanoparticles on file fatigue and failure. Dynamic x-ray diffraction, nanoindentation and torque measurements all indicate a significant improvement in the fatigue resistance and time to breakage of the coated files, stemming from reduced friction between the file and the surrounding tissue. These methods are possibly applicable to a variety of NiTi-based medical devices where fatigue and consequent failure are of relevance.

Research paper thumbnail of Influence of Inorganic WS2 Nanoparticles on the Trobological Properties of Epoxy Resin

Research paper thumbnail of Tribological and Adhesion Properties of CVD Diamond Films Grown on Steel with a Cr‐N Interlayer

In the present work we investigate friction and adhesion properties of microcrystalline diamond f... more In the present work we investigate friction and adhesion properties of microcrystalline diamond films grown on steel substrates with a Cr-N interlayer prepared at 500° C and 800° C. Scratch tests were performed at indentation loads of 1-4 N and sliding velocity of 0.08 mm/s. The friction coefficient and wear loss were assessed. The diamond film structure and composition are

Research paper thumbnail of Friction and wear of copper samples in the steady friction state

Tribology International, 2010

The effect of sliding velocity and load on the friction and wear of Cu–steel pairs was studied. E... more The effect of sliding velocity and load on the friction and wear of Cu–steel pairs was studied. Elasto-hydrodynamic (EHL), mixed (ML) and boundary lubrication (BL) regions were analyzed using the Stribeck curve. The lubrication number of Schipper, Z, was used in the analysis of the Stribeck curve. Steady friction states were observed in the mixed EHL and BL regions, however

Research paper thumbnail of Steel surface modification by pulsed air arc treatment

Surface and Coatings Technology, 2010

Pulsed air arc treatment (PAAT) was used to modify the surface morphology and phase composition o... more Pulsed air arc treatment (PAAT) was used to modify the surface morphology and phase composition of 5010 and 01 steel. The arc produced local heating and eroded the steel surface forming craters, and the subsequent modification depended on the crater density. X-ray diffraction showed that the volume fraction of ferrite decreased while that of austenite increased with crater density. Cementite

Research paper thumbnail of Dislocation Structure and Stick–Slip Phenomenon

Tribology Letters, 2014

Friction is a complex process involving multiscale asperity contact and large plastic deformation... more Friction is a complex process involving multiscale asperity contact and large plastic deformation associated with the development of a dislocation structure. Friction is closely associated with the stick-slip phenomenon. In spite of the large number of papers, dedicated to stick-slip effects, little effort has been directed toward elucidating the development of the dislocation structure during stick-slip phenomena. Here, we report some new systematic investigations into the dislocation nature of stick-slips during low-velocity friction of a lithium fluoride single crystal rubbed against a spherical diamond indenter. It is shown that the average velocity of the indenter in the stick phase is about 300 times lower than the maximal velocity in the slip. This difference in velocities leads to entirely different dislocation behavior and damage development in the stick and slips phases. The stick phase is mainly determined by time-dependent strain (creep) wherein, as in metals and alloys, three stages of creep are observed. Based on the analysis of the dislocation structure, a model of the dislocation distribution in the regions of stick (creep) and slip is proposed.

Research paper thumbnail of Static and Kinetic Friction of Smooth Glass Surfaces Rubbed With Silicone Oils

World Tribology Congress III, Volume 1, 2005

ABSTRACT The study of the effect of waiting time, loading and unloading on static and kinetic fri... more ABSTRACT The study of the effect of waiting time, loading and unloading on static and kinetic friction for real contact micro-systems was carried out. Three types of silicone fluid with the viscosity of 100, 450 and 5000 cSt at 25° C were used. Stop-start experiments allowed us to estimate the relaxation time after the static friction overshoot. For silicone liquid with viscosity of 100 cSt, relaxation of friction force (F) after the static friction overshoot occurred over one cycle of testing. Relaxation of F for fluids with the viscosity of 450 and 5000 cSt occurred during a long time and this effect was opposite for these silicone liquids. The analysis of loading-unloading cycles showed only a partial reversibility of F. The results were compared with static friction and stick-slip data obtained in other works, using SFA and FFM techniques. In order to explain the effect of viscosity and structure of the lubricant layers on stick-slip phenomenon, interior and wall slip of the lubricant film is discussed.

Research paper thumbnail of Tribological performance of the epoxy-based composite reinforced by WS 2 fullerene-like nanoparticles and nanotubes

physica status solidi (a), 2013

ABSTRACT Recently large amounts of inorganic nanotubes (INT) and inorganic fullerene-like (IF) na... more ABSTRACT Recently large amounts of inorganic nanotubes (INT) and inorganic fullerene-like (IF) nanoparticles of WS2 became available and methods for their dispersion in different media were developed. In the present work the tribological properties of epoxy composite compounded with tungsten disulfide particles of different sizes and morphologies, including quasi-spherical IF nanoparticles, one-dimensional INT as well as micron-size platelets (2H) were investigated. The coefficient of friction and wear loss were measured under dry contact conditions using different tribological rigs. Remarkable reduction in wear and also friction (under high load) was demonstrated for the IF/INT epoxy nanocomposite. The reduced wear is attributed in general to the reinforcement of the polymer matrix by nanoparticles and the simultaneous reduction of the epoxy brittleness. Contrarily, the friction of the neat epoxy sample and epoxy mixed with platelets was accompanied with strong wear and transfer of a polymer film onto the rubbed surfaces. These results are consistent with the recently reported improvements in the fracture toughness, peel and shear strength of the epoxy-nanoparticles (IF/INT) composites.

Research paper thumbnail of Friction, wear and plastic deformation of Cu and α/β brass under lubrication conditions

Wear, 2014

ABSTRACT Friction, wear and plastic deformation of copper (Cu) and α/β brass were studied under l... more ABSTRACT Friction, wear and plastic deformation of copper (Cu) and α/β brass were studied under lubrication conditions. Hardness and microstructure of surface layers were evaluated. The friction properties were presented by Stribeck curves. The friction coefficient and wear of brass were significantly larger in comparison to Cu. The critical load of transition from the elasto-hydrodynamic lubrication (EHL) to boundary lubrication (BL) was two times lower for brass. Superplastic deformation of α-phase grains in brass is appeared under friction in BL, whereas plastic deformation localized at thin surface layers is observed for Cu. Intragranular sliding in α-phase is accompanied with the formation of shear bands and many pores coalesced to cracks. Thickness of the wear particles of brass is close to the width of shear bands. The deformation hardness of brass is significantly higher in comparison to Cu rubbed in the BL region.

Research paper thumbnail of Friction and Wear of MoS

Volume 3: Design; Tribology; Education, 2008

Incorporation of solid lubricant into micro-reservoirs produced by Laser Surface Texturing (LST) ... more Incorporation of solid lubricant into micro-reservoirs produced by Laser Surface Texturing (LST) and its effect on the tribological properties of surfaces under dry friction is studied. The density of the dimple reservoirs and the height of the bulges around them are investigated in terms of the longevity of solid lubricant films burnished on LST steel surfaces. Friction tests were performed using a ball-on-flat device. Optimum density (40-50%) of the dimples is revealed. It is shown that the adhesion of solid lubricant in the space between the dimples is provided by mechanical engagement of particles in the rough surface and by smearing the solid lubricant around the dimples. Best results are obtained with the surfaces that were lapped to half of the height of bulges. Long wear life of burnished film on LST steel surfaces is apparently provided by preservation of thin MoS 2 film around the bulges and by supply of solid lubricant from the dimples to the surface.

Research paper thumbnail of Tungsten Disulfide Inorganic Nanotubes Functionalized by PTFE for Friction Application

Tungsten Disulfide Inorganic Nanotubes Functionalized by PTFE for Friction Application, 2021

Inorganic nanotubes (INTs) and fullerene-like nanoparticles (NPs) of WS2/MoS2 penetrate and exfol... more Inorganic nanotubes (INTs) and fullerene-like nanoparticles (NPs) of WS2/MoS2 penetrate and exfoliate at the contact interface and facilitate tribofilm formation. While the tribological properties are greatly improved by exfoliated NPs that shed easily, they may be diminished by agglomeration in oil. Therefore, surface functionalization is employed to improve dispersion in oil-based suspensions. Here, WS2 INTs were functionalized by polytetrafluoroethylene (PTFE) in a simple and cost-effective bath sonication method. WS2-INTs with two concentrations of added PTFE were characterized by scanning and transmission electron microscopy, micro-Raman spectroscopy, and thermogravimetric analysis. Superior distribution of WS2 was observed before and during friction experiments. Chemical analysis showed a significantly greater amount of PTFE-coated INTs on rubbed surfaces, in accordance with the improved friction and wear properties.

Research paper thumbnail of Friction, wear and deformed structure of Ag and Ni under early stages of scratching

Research paper thumbnail of Electrophoretic Deposition of Hydroxyapatite Film Containing Re-Doped MoS2 Nanoparticles

International Journal of Molecular Sciences

Films combining hydroxyapatite (HA) with minute amounts (ca. 1 weight %) of (rhenium doped) fulle... more Films combining hydroxyapatite (HA) with minute amounts (ca. 1 weight %) of (rhenium doped) fullerene-like MoS 2 (IF) nanoparticles were deposited onto porous titanium substrate through electrophoretic process (EPD). The films were analyzed by scanning electron microscopy (SEM), X-ray diffraction and Raman spectroscopy. The SEM analysis showed relatively uniform coatings of the HA + IF on the titanium substrate. Chemical composition analysis using energy dispersive X-ray spectroscopy (EDS) of the coatings revealed the presence of calcium phosphate minerals like hydroxyapatite, as a majority phase. Tribological tests were undertaken showing that the IF nanoparticles endow the HA film very low friction and wear characteristics. Such films could be of interest for various medical technologies. Means for improving the adhesion of the film to the underlying substrate and its fracture toughness, without compromising its biocompatibility are discussed at the end.

Research paper thumbnail of Effect of Stacking-Fault Energy on the Deformed Structures and Work Hardening of Ag and Ni after Scratching during Early Loading Stage

Journal of Materials Engineering and Performance

Research paper thumbnail of Effect of Plastic Deformation and Damage Development during Friction of fcc Metals in the Conditions of Boundary Lubrication

Lubricants

The main goal of the presented work was the analysis of the interaction between deformed microstr... more The main goal of the presented work was the analysis of the interaction between deformed microstructures and friction and the wear properties of four face centered cubic (fcc) metals. Pure fcc metals such as Ag, Cu, Ni, and Al with different values of stacking fault energy (SFE) were chosen for pin-on-disk tests in lubricated conditions. Friction properties of the four fcc metals are presented herein as their Stribeck curves. The transition from elasto-hydrodynamic lubrication (EHL) to boundary lubrication (BL) regions depends mainly on the values of SFE, hardness, and contact temperature. The acoustic emission (AE) parameters were analyzed in the transition from the EHL to the BL region. The models of friction in different lubricant conditions related to the AE waveforms were proposed. The nanocrystalline top surface layers characterized the deformed structure during friction of Ag in the BL region. The lamellar cross-sectional microstructure was formed in the subsurface layers of ...

Research paper thumbnail of Deformation Microstructure and Chemical Composition of Surface Layers of Cu and Al Under Friction in Lubricated Conditions

Research paper thumbnail of Microstructure and nanohardness of Ag and Ni under friction in boundary lubrication

Research paper thumbnail of Testing of WS2 Nanoparticles Functionalized by a Humin-Like Shell as Lubricant Additives

Lubricants

Nanoparticles of transition metal dichalcogenides (TMDC) have been known to reduce friction and w... more Nanoparticles of transition metal dichalcogenides (TMDC) have been known to reduce friction and wear when added to oil-type liquid lubricants. Aggregation limits the ability of the nanoparticles to penetrate into the interface between the two rubbing surfaces-an important factor in friction reduction mechanisms. Doping has been successfully used to reduce agglomeration, but it must be done in the production process of the nanoparticles. The use of surface-functionalized nanoparticles is less common than doping. Nonetheless, it has the potential to reduce agglomeration and thereby improve the reduction of friction and wear. In this study, we present the results of preliminary tribological ball-on-flat tests performed with WS 2 nanoparticles functionalized by a humin-like conformal shell, as additives to polyalphaolefin-4 (PAO-4) oil. We tested WS 2 inorganic nanotubes (INTs) and two grades of inorganic fullerene-like nanoparticles (IFs). The shell/coating was found to improve friction reduction for IFs but not for INTs through better dispersion in the oil. The thicker the coating on the IFs, the less agglomerated they were. Coated industrial-grade IFs were found, by far, to be the best additive for friction reduction. We suggest the combination between reduced agglomeration and poor crystallinity as the reason for this result.

Research paper thumbnail of Electrophoretic Deposition of Hydroxyapatite Film Containing Re-Doped MoS₂ Nanoparticles

International journal of molecular sciences, Jan 26, 2018

Films combining hydroxyapatite (HA) with minute amounts (ca. 1 weight %) of (rhenium doped) fulle... more Films combining hydroxyapatite (HA) with minute amounts (ca. 1 weight %) of (rhenium doped) fullerene-like MoS₂ (IF) nanoparticles were deposited onto porous titanium substrate through electrophoretic process (EPD). The films were analyzed by scanning electron microscopy (SEM), X-ray diffraction and Raman spectroscopy. The SEM analysis showed relatively uniform coatings of the HA + IF on the titanium substrate. Chemical composition analysis using energy dispersive X-ray spectroscopy (EDS) of the coatings revealed the presence of calcium phosphate minerals like hydroxyapatite, as a majority phase. Tribological tests were undertaken showing that the IF nanoparticles endow the HA film very low friction and wear characteristics. Such films could be of interest for various medical technologies. Means for improving the adhesion of the film to the underlying substrate and its fracture toughness, without compromising its biocompatibility are discussed at the end.

Research paper thumbnail of Study of the transition from EHL to BL regions under friction of Ag and Ni. I. Analysis of acoustic emission

Tribology International, 2017

Research paper thumbnail of Alleviating fatigue and failure of NiTi endodontic files by a coating containing inorganic fullerene-like WS2 nanoparticles

Journal of Materials Research, May 27, 2011

Nickel-titanium (NiTi) alloys combine several remarkable characteristics, among them are shapemem... more Nickel-titanium (NiTi) alloys combine several remarkable characteristics, among them are shapememory, superelasticity, great strain recovery, good biocompatibility, and corrosion resistance. These render them well suited to a wide range of medical applications, such as cardiovascular stents, laparoscopy, and dental applications such as NiTi endodontic files (EFs) used for root canal treatment, which are the focus of this work. Unfortunately, fatigue-induced and incidental failure of NiTi EFs is not uncommon, which may lead to severe medical consequences. Here we examine the effects of cobalt coatings with impregnated fullerene-like WS 2 nanoparticles on file fatigue and failure. Dynamic x-ray diffraction, nanoindentation and torque measurements all indicate a significant improvement in the fatigue resistance and time to breakage of the coated files, stemming from reduced friction between the file and the surrounding tissue. These methods are possibly applicable to a variety of NiTi-based medical devices where fatigue and consequent failure are of relevance.

Research paper thumbnail of Influence of Inorganic WS2 Nanoparticles on the Trobological Properties of Epoxy Resin

Research paper thumbnail of Tribological and Adhesion Properties of CVD Diamond Films Grown on Steel with a Cr‐N Interlayer

In the present work we investigate friction and adhesion properties of microcrystalline diamond f... more In the present work we investigate friction and adhesion properties of microcrystalline diamond films grown on steel substrates with a Cr-N interlayer prepared at 500° C and 800° C. Scratch tests were performed at indentation loads of 1-4 N and sliding velocity of 0.08 mm/s. The friction coefficient and wear loss were assessed. The diamond film structure and composition are

Research paper thumbnail of Friction and wear of copper samples in the steady friction state

Tribology International, 2010

The effect of sliding velocity and load on the friction and wear of Cu–steel pairs was studied. E... more The effect of sliding velocity and load on the friction and wear of Cu–steel pairs was studied. Elasto-hydrodynamic (EHL), mixed (ML) and boundary lubrication (BL) regions were analyzed using the Stribeck curve. The lubrication number of Schipper, Z, was used in the analysis of the Stribeck curve. Steady friction states were observed in the mixed EHL and BL regions, however

Research paper thumbnail of Steel surface modification by pulsed air arc treatment

Surface and Coatings Technology, 2010

Pulsed air arc treatment (PAAT) was used to modify the surface morphology and phase composition o... more Pulsed air arc treatment (PAAT) was used to modify the surface morphology and phase composition of 5010 and 01 steel. The arc produced local heating and eroded the steel surface forming craters, and the subsequent modification depended on the crater density. X-ray diffraction showed that the volume fraction of ferrite decreased while that of austenite increased with crater density. Cementite

Research paper thumbnail of Dislocation Structure and Stick–Slip Phenomenon

Tribology Letters, 2014

Friction is a complex process involving multiscale asperity contact and large plastic deformation... more Friction is a complex process involving multiscale asperity contact and large plastic deformation associated with the development of a dislocation structure. Friction is closely associated with the stick-slip phenomenon. In spite of the large number of papers, dedicated to stick-slip effects, little effort has been directed toward elucidating the development of the dislocation structure during stick-slip phenomena. Here, we report some new systematic investigations into the dislocation nature of stick-slips during low-velocity friction of a lithium fluoride single crystal rubbed against a spherical diamond indenter. It is shown that the average velocity of the indenter in the stick phase is about 300 times lower than the maximal velocity in the slip. This difference in velocities leads to entirely different dislocation behavior and damage development in the stick and slips phases. The stick phase is mainly determined by time-dependent strain (creep) wherein, as in metals and alloys, three stages of creep are observed. Based on the analysis of the dislocation structure, a model of the dislocation distribution in the regions of stick (creep) and slip is proposed.

Research paper thumbnail of Static and Kinetic Friction of Smooth Glass Surfaces Rubbed With Silicone Oils

World Tribology Congress III, Volume 1, 2005

ABSTRACT The study of the effect of waiting time, loading and unloading on static and kinetic fri... more ABSTRACT The study of the effect of waiting time, loading and unloading on static and kinetic friction for real contact micro-systems was carried out. Three types of silicone fluid with the viscosity of 100, 450 and 5000 cSt at 25° C were used. Stop-start experiments allowed us to estimate the relaxation time after the static friction overshoot. For silicone liquid with viscosity of 100 cSt, relaxation of friction force (F) after the static friction overshoot occurred over one cycle of testing. Relaxation of F for fluids with the viscosity of 450 and 5000 cSt occurred during a long time and this effect was opposite for these silicone liquids. The analysis of loading-unloading cycles showed only a partial reversibility of F. The results were compared with static friction and stick-slip data obtained in other works, using SFA and FFM techniques. In order to explain the effect of viscosity and structure of the lubricant layers on stick-slip phenomenon, interior and wall slip of the lubricant film is discussed.

Research paper thumbnail of Tribological performance of the epoxy-based composite reinforced by WS 2 fullerene-like nanoparticles and nanotubes

physica status solidi (a), 2013

ABSTRACT Recently large amounts of inorganic nanotubes (INT) and inorganic fullerene-like (IF) na... more ABSTRACT Recently large amounts of inorganic nanotubes (INT) and inorganic fullerene-like (IF) nanoparticles of WS2 became available and methods for their dispersion in different media were developed. In the present work the tribological properties of epoxy composite compounded with tungsten disulfide particles of different sizes and morphologies, including quasi-spherical IF nanoparticles, one-dimensional INT as well as micron-size platelets (2H) were investigated. The coefficient of friction and wear loss were measured under dry contact conditions using different tribological rigs. Remarkable reduction in wear and also friction (under high load) was demonstrated for the IF/INT epoxy nanocomposite. The reduced wear is attributed in general to the reinforcement of the polymer matrix by nanoparticles and the simultaneous reduction of the epoxy brittleness. Contrarily, the friction of the neat epoxy sample and epoxy mixed with platelets was accompanied with strong wear and transfer of a polymer film onto the rubbed surfaces. These results are consistent with the recently reported improvements in the fracture toughness, peel and shear strength of the epoxy-nanoparticles (IF/INT) composites.

Research paper thumbnail of Friction, wear and plastic deformation of Cu and α/β brass under lubrication conditions

Wear, 2014

ABSTRACT Friction, wear and plastic deformation of copper (Cu) and α/β brass were studied under l... more ABSTRACT Friction, wear and plastic deformation of copper (Cu) and α/β brass were studied under lubrication conditions. Hardness and microstructure of surface layers were evaluated. The friction properties were presented by Stribeck curves. The friction coefficient and wear of brass were significantly larger in comparison to Cu. The critical load of transition from the elasto-hydrodynamic lubrication (EHL) to boundary lubrication (BL) was two times lower for brass. Superplastic deformation of α-phase grains in brass is appeared under friction in BL, whereas plastic deformation localized at thin surface layers is observed for Cu. Intragranular sliding in α-phase is accompanied with the formation of shear bands and many pores coalesced to cracks. Thickness of the wear particles of brass is close to the width of shear bands. The deformation hardness of brass is significantly higher in comparison to Cu rubbed in the BL region.

Research paper thumbnail of Friction and Wear of MoS

Volume 3: Design; Tribology; Education, 2008

Incorporation of solid lubricant into micro-reservoirs produced by Laser Surface Texturing (LST) ... more Incorporation of solid lubricant into micro-reservoirs produced by Laser Surface Texturing (LST) and its effect on the tribological properties of surfaces under dry friction is studied. The density of the dimple reservoirs and the height of the bulges around them are investigated in terms of the longevity of solid lubricant films burnished on LST steel surfaces. Friction tests were performed using a ball-on-flat device. Optimum density (40-50%) of the dimples is revealed. It is shown that the adhesion of solid lubricant in the space between the dimples is provided by mechanical engagement of particles in the rough surface and by smearing the solid lubricant around the dimples. Best results are obtained with the surfaces that were lapped to half of the height of bulges. Long wear life of burnished film on LST steel surfaces is apparently provided by preservation of thin MoS 2 film around the bulges and by supply of solid lubricant from the dimples to the surface.