15 results on '"Tomas F"'
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2. Quality Control Metrics to Assess MoS2 Sputtered Films for Tribological Applications
- Author
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Babuska, Tomas F., Curry, John F., Dugger, Michael T., Jones, Morgan R., DelRio, Frank W., Lu, Ping, Xin, Yan, Grejtak, Tomas, Chrostowski, Robert, Mangolini, Filippo, Strandwitz, Nicholas C., Chowdhury, Md Istiaque, Doll, Gary L., and Krick, Brandon A.
- Published
- 2022
- Full Text
- View/download PDF
3. Linking Friction Scales from Nano to Macro via Avalanches
- Author
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Salners, Tyler, Curry, John F., Hinkle, Adam R., Babuska, Tomas F., Argibay, Nicolas, DelRio, Frank W., Chandross, Michael, and Dahmen, Karin
- Published
- 2022
- Full Text
- View/download PDF
4. Perfluoroalkoxy (PFA)-α-Alumina Composites: Effect of Environment on Tribological Performance
- Author
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Sidebottom, Mark A., Atkinson, Cooper A., Campbell, Kasey L., Babuska, Tomas F., Junk, Christopher P., Burch, Heidi E., and Krick, Brandon A.
- Published
- 2019
- Full Text
- View/download PDF
5. Ultralow Wear Behavior of Iron–Cobalt-Filled PTFE Composites
- Author
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Kylie E. Van Meter, Tomas F. Babuska, Christopher P. Junk, Kasey L. Campbell, Mark A. Sidebottom, Tomas Grejtak, Andrew B. Kustas, and Brandon A. Krick
- Subjects
Mechanics of Materials ,Mechanical Engineering ,Surfaces and Interfaces ,Surfaces, Coatings and Films - Published
- 2022
6. Ultralow Wear Behavior of Iron–Cobalt-Filled PTFE Composites
- Author
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Van Meter, Kylie E., primary, Babuska, Tomas F., additional, Junk, Christopher P., additional, Campbell, Kasey L., additional, Sidebottom, Mark A., additional, Grejtak, Tomas, additional, Kustas, Andrew B., additional, and Krick, Brandon A., additional
- Published
- 2022
- Full Text
- View/download PDF
7. Quality Control Metrics to Assess MoS2 Sputtered Films for Tribological Applications
- Author
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Tomas F. Babuska, John F. Curry, Michael T. Dugger, Morgan R. Jones, Frank W. DelRio, Ping Lu, Yan Xin, Tomas Grejtak, Robert Chrostowski, Filippo Mangolini, Nicholas C. Strandwitz, Md Istiaque Chowdhury, Gary L. Doll, and Brandon A. Krick
- Subjects
Mechanics of Materials ,Mechanical Engineering ,Surfaces and Interfaces ,Surfaces, Coatings and Films - Abstract
Pure molybdenum disulfide (MoS2) solid lubricant coatings could attain densities comparable to doped films (and the associated benefits to wear rate and environmental stability) through manipulation of the microstructure via deposition parameters. Unfortunately, pure films can exhibit highly variable microstructures and mechanical properties due to processes that are not controlled during deposition (i.e., batch-to-batch variation). This work focuses on developing a relationship between density, hardness, friction, and wear for pure sputtered MoS2 coatings. Results show that dense films (ρ = 4.5 g/cm3) exhibit a 100 × lower wear rate compared to porous coatings (ρ = 3.04–3.55 g/cm3). The tribological performance of high density pure MoS2 coatings is shown to surpass that of established composite coatings, achieving a wear rate 2 × (k = 5.74 × 10–8 mm3/Nm) lower than composite MoS2/Sb2O3/Au in inert environments.
- Published
- 2022
8. Linking Friction Scales from Nano to Macro via Avalanches
- Author
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Tyler Salners, John F. Curry, Adam R. Hinkle, Tomas F. Babuska, Nicolas Argibay, Frank W. DelRio, Michael Chandross, and Karin Dahmen
- Subjects
Mechanics of Materials ,Mechanical Engineering ,Surfaces and Interfaces ,Surfaces, Coatings and Films - Abstract
Steady-state fluctuations in the friction force of molybdenum disulfide (MoS2), a prototypical lamellar solid, were analyzed experimentally for newton-scale forces and computationally via molecular dynamics simulations for nanonewton-scale forces. A mean field model links the statics and the dynamics of the friction behavior across these eight orders of magnitude in friction force and six orders of magnitude in friction force fluctuations (i.e., avalanches). Both the statistics and dynamics of the avalanches match model predictions, indicating that friction can be characterized as a series of avalanches with properties that are predictable over a wide range of scales.
- Published
- 2022
9. Quality Control Metrics to Assess MoS2 Sputtered Films for Tribological Applications.
- Author
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Babuska, Tomas F., Curry, John F., Dugger, Michael T., Jones, Morgan R., DelRio, Frank W., Lu, Ping, Xin, Yan, Grejtak, Tomas, Chrostowski, Robert, Mangolini, Filippo, Strandwitz, Nicholas C., Chowdhury, Md Istiaque, Doll, Gary L., and Krick, Brandon A.
- Abstract
Pure molybdenum disulfide (MoS2) solid lubricant coatings could attain densities comparable to doped films (and the associated benefits to wear rate and environmental stability) through manipulation of the microstructure via deposition parameters. Unfortunately, pure films can exhibit highly variable microstructures and mechanical properties due to processes that are not controlled during deposition (i.e., batch-to-batch variation). This work focuses on developing a relationship between density, hardness, friction, and wear for pure sputtered MoS2 coatings. Results show that dense films (ρ = 4.5 g/cm3) exhibit a 100 × lower wear rate compared to porous coatings (ρ = 3.04–3.55 g/cm3). The tribological performance of high density pure MoS2 coatings is shown to surpass that of established composite coatings, achieving a wear rate 2 × (k = 5.74 × 10–8 mm3/Nm) lower than composite MoS2/Sb2O3/Au in inert environments. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
10. Structurally Driven Environmental Degradation of Friction in MoS2 Films
- Author
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Nicolas Argibay, Morgan R. Jones, Brandon A. Krick, Philip Mantos, Michael T. Dugger, Taisuke Ohta, N. Scott Bobbitt, Frank W. DelRio, Tomas F. Babuska, John F. Curry, and Michael Chandross
- Subjects
Kelvin probe force microscope ,Materials science ,Mechanical Engineering ,02 engineering and technology ,Surfaces and Interfaces ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Shear (sheet metal) ,Molecular dynamics ,Mechanics of Materials ,Microscopy ,Work function ,Surface layer ,Thin film ,Composite material ,0210 nano-technology ,Nanoscopic scale - Abstract
We report an investigation of the friction mechanisms of MoS2 thin films under changing environments and contact conditions using a variety of computational and experimental techniques. Molecular dynamics simulations were used to study the effects of water and molecular oxygen on friction and bonding of MoS2 lamellae during initial sliding. Characterization via photoelectron emission microscopy (PEEM) and Kelvin probe force microscopy (KPFM) were used to determine work function changes in shear modified material within the top few nanometers of MoS2 wear scars. The work function was shown to change with contact conditions and environment, and shown by density functional theory (DFT) calculations and literature reports to be correlated with lamellae size and thickness of the basally oriented surface layer. Results from nanoscale simulations and macroscale experiments suggest that the evolution of the friction behavior of MoS2 is linked primarily to the formation or inhibition of a basally oriented, molecularly thin surface film with long-range order.
- Published
- 2021
11. Perfluoroalkoxy (PFA)-α-Alumina Composites: Effect of Environment on Tribological Performance
- Author
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Brandon A. Krick, Kasey L. Campbell, Christopher P. Junk, Tomas F. Babuska, Heidi Elizabeth Burch, Mark A. Sidebottom, and Cooper A. Atkinson
- Subjects
chemistry.chemical_classification ,Materials science ,Abrasion (mechanical) ,Mechanical Engineering ,Composite number ,chemistry.chemical_element ,02 engineering and technology ,Surfaces and Interfaces ,Polymer ,Tribology ,021001 nanoscience & nanotechnology ,Nitrogen ,Surfaces, Coatings and Films ,chemistry.chemical_compound ,020303 mechanical engineering & transports ,0203 mechanical engineering ,chemistry ,13. Climate action ,Mechanics of Materials ,Relative humidity ,Carboxylate ,Composite material ,0210 nano-technology ,Tribometer - Abstract
Perfluoroalkoxy polymer (PFA)-α-phase alumina (α-Al2O3) composites have dramatically (~ 10,000 ×) improved wear resistance compared to unfilled PFA when tested in air. In this study, unfilled PFA and PFA-α-Al2O3 composites were tested using a linear reciprocating tribometer in dry nitrogen (< 2.5 ppm O2 and H2O), humidity-controlled air (15%, 30%, and 45% relative humidity), and submerged water. PFA-α-Al2O3 tested in dry nitrogen (N2) and in submerged water exhibited wear rates that were two to three orders of magnitude higher than those of PFA-α-Al2O3 composites tested in humidity-controlled air. Infrared spectra of the worn PFA-α-Al2O3 surfaces tested in air exhibited peaks attributed to carboxylate salts. These peaks were severely diminished on the PFA-α-Al2O3 sample tested in dry N2 and not observed for submerged water environments. The high wear rate of PFA-α-Al2O3 tested in dry N2 and submerged water was attributed to the lack of carboxylate salts, which require oxygen and water form. These carboxylate salts bond to the α-Al2O3 filler within the PFA matrix which reinforces the polymer wear surface. Additionally, these carboxylate salts form a transfer film on the stainless steel counterface, which protects both the composite and counterface from wear and abrasion.
- Published
- 2019
12. Perfluoroalkoxy (PFA)-α-Alumina Composites: Effect of Environment on Tribological Performance.
- Author
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Sidebottom, Mark A., Atkinson, Cooper A., Campbell, Kasey L., Babuska, Tomas F., Junk, Christopher P., Burch, Heidi E., and Krick, Brandon A.
- Abstract
Perfluoroalkoxy polymer (PFA)-α-phase alumina (α-Al
2 O3 ) composites have dramatically (~ 10,000 ×) improved wear resistance compared to unfilled PFA when tested in air. In this study, unfilled PFA and PFA-α-Al2 O3 composites were tested using a linear reciprocating tribometer in dry nitrogen (< 2.5 ppm O2 and H2 O), humidity-controlled air (15%, 30%, and 45% relative humidity), and submerged water. PFA-α-Al2 O3 tested in dry nitrogen (N2 ) and in submerged water exhibited wear rates that were two to three orders of magnitude higher than those of PFA-α-Al2 O3 composites tested in humidity-controlled air. Infrared spectra of the worn PFA-α-Al2 O3 surfaces tested in air exhibited peaks attributed to carboxylate salts. These peaks were severely diminished on the PFA-α-Al2 O3 sample tested in dry N2 and not observed for submerged water environments. The high wear rate of PFA-α-Al2 O3 tested in dry N2 and submerged water was attributed to the lack of carboxylate salts, which require oxygen and water form. These carboxylate salts bond to the α-Al2 O3 filler within the PFA matrix which reinforces the polymer wear surface. Additionally, these carboxylate salts form a transfer film on the stainless steel counterface, which protects both the composite and counterface from wear and abrasion. [ABSTRACT FROM AUTHOR]- Published
- 2020
- Full Text
- View/download PDF
13. Temperature-Dependent Friction and Wear of MoS2/Sb2O3/Au Nanocomposites
- Author
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Nicolas Argibay, John F. Curry, Tomas F. Babuska, and M. T. Brumbach
- Subjects
Nanocomposite ,Materials science ,Mechanical Engineering ,Composite number ,02 engineering and technology ,Surfaces and Interfaces ,Low friction ,021001 nanoscience & nanotechnology ,Surface film ,Surfaces, Coatings and Films ,Auger ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Mechanics of Materials ,Composite material ,0210 nano-technology ,Inert gas - Abstract
The temperature-dependent friction and wear of magnetron-sputtered MoS2/Sb2O3/Au nanocomposites was investigated in the range −150 to 150 °C using macroscale experiments. We investigate the origin of recent reports suggesting the existence of a relatively high friction (µ ~ 0.2) transition for these nanocomposites at temperatures below −20 °C, contrasting with the characteristic ultra-low friction behavior (µ
- Published
- 2016
14. Highly Oriented MoS2 Coatings: Tribology and Environmental Stability
- Author
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Ashlie Martini, Nicolas Argibay, Nicholas C. Strandwitz, Brandon A. Krick, John F. Curry, Tomas F. Babuska, Brendan L Nation, and Michael T. Dugger
- Subjects
Materials science ,Mechanical Engineering ,Metallurgy ,chemistry.chemical_element ,02 engineering and technology ,Surfaces and Interfaces ,Substrate (electronics) ,Surface finish ,Tribology ,021001 nanoscience & nanotechnology ,Nitrogen ,Surfaces, Coatings and Films ,chemistry.chemical_compound ,020303 mechanical engineering & transports ,0203 mechanical engineering ,chemistry ,Mechanics of Materials ,Shear strength ,Composite material ,0210 nano-technology ,Molybdenum disulfide ,Water vapor ,Deposition (law) - Abstract
Molybdenum disulfide (MoS2) coatings have been prepared via nitrogen (N2) spray deposition, a process which deliberately impinges particulates of MoS2 onto a substrate yielding a preferential basally oriented state. Adherent and highly oriented 100- to 300-nm-thick coatings were produced. These coatings exhibited lower initial friction coefficients than sputtered films in dry and humid environments. Such reductions likely stem from a higher degree of basal plane orientation throughout the film as confirmed by XRD. Initial friction in humid air for sprayed coatings (µ = 0.10) was half that of sputtered coatings (µ = 0.21), showing the ability of oriented surface films to produce a low shear strength interface. Aging of these coatings in a humid nitrogen environment also showed the propensity for the films to resist poisoning of their structure which could otherwise result in degraded tribological performance. These results also support the hypothesis that water vapor does not contribute to the oxidation of MoS2.
- Published
- 2016
15. Temperature-Dependent Friction and Wear Behavior of PTFE and MoS2
- Author
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Nicolas Argibay, Wallace Gregory Sawyer, Morgan R. Jones, Angela A. Pitenis, Tomas F. Babuska, and Brendan L Nation
- Subjects
Materials science ,Physics::Instrumentation and Detectors ,Mechanical Engineering ,Friction modifier ,02 engineering and technology ,Surfaces and Interfaces ,Dissipation ,021001 nanoscience & nanotechnology ,Surfaces, Coatings and Films ,chemistry.chemical_compound ,Hysteresis ,020303 mechanical engineering & transports ,0203 mechanical engineering ,chemistry ,Deformation mechanism ,Rheology ,Mechanics of Materials ,Relaxation (physics) ,Lubricant ,Composite material ,0210 nano-technology ,Molybdenum disulfide - Abstract
An investigation of the temperature-dependent friction behavior of PTFE, MoS2, and PTFE-on-MoS2 is presented. Friction behavior was measured while continuously varying contact temperature in the range −150 to 175 °C while sliding in dry nitrogen, as well as for self-mated PTFE immersed in liquid nitrogen. These results contrast with previous reports of high-friction transitions and plateaus for pure and composite MoS2 at temperatures below about −20 °C; instead, we have found persistently weak thermal behavior between 0 and −196 °C, providing new insight about the molecular mechanisms of macroscale friction. The temperature-dependent friction behavior characteristic of self-mated PTFE was found also for PTFE-on-MoS2 sliding contacts, suggesting that PTFE friction was defined by subsurface deformation mechanisms and internal friction even when sliding against a lamellar lubricant with extremely low friction coefficient (µ ~ 0.02). The various relaxation temperatures of PTFE were found in the temperature-dependent friction behavior, showing excellent agreement with reported values acquired using rheological techniques measuring energy dissipation through internal friction. Additionally, hysteresis in friction behavior suggests an increase in near-surface crystallinity upon exceeding the high-temperature relaxation, T α ~ 116 °C.
- Published
- 2016
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